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• Can PPP CHAP authentication use Cisco "Type 5" MD5 passwords?

  - by romandas

  Looking over Cisco's documentation, and RFC 1994 (PPP CHAP authentication), my initial guess is "no", because CHAP requires a cleartext password to rehash every time it sends a challenge. Is this true? If so, is there another way to configure CHAP so it doesn't use the easily-decoded type 7 passwords? The Cisco device in question uses local authentication, not a TACACS+ or RADIUS server. Would using RADIUS eliminate the problem or just move it to the RADIUS server?

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• Computer Networks UNISA - Chap 12 – Networking Security

  - by MarkPearl

  After reading this section you should be able to Identify security risks in LANs and WANs and design security policies that minimize risks Explain how physical security contributes to network security Discuss hardware and design based security techniques Understand methods of encryption such as SSL and IPSec, that can secure data in storage and in transit Describe how popular authentication protocols such as RADIUS< TACACS,Kerberos, PAP, CHAP, and MS-CHAP function Use network operating system techniques to provide basic security Understand wireless security protocols such as WEP, WPA and 802.11i Security Audits Before spending time and money on network security, examine your networks security risks – rate and prioritize risks. Different organizations have different levels of network security requirements. Security Risks Not all security breaches result from a manipulation of network technology – there are human factors that can play a role as well. The following categories are areas of considerations… Risks associated with People Risks associated with Transmission and Hardware Risks associated with Protocols and Software Risks associated with Internet Access An effective security policy A security policy identifies your security goals, risks, levels of authority, designated security coordinator and team members, responsibilities for each team member, and responsibilities for each employee. In addition it specifies how to address security breaches. It should not state exactly which hardware, software, architecture, or protocols will be used to ensure security, nor how hardware or software will be installed and configured. A security policy must address an organizations specific risks. to understand your risks, you should conduct a security audit that identifies vulnerabilities and rates both the severity of each threat and its likelihood of occurring. Security Policy Content Security policy content should… Policies for each category of security Explain to users what they can and cannot do and how these measures protect the networks security Should define what confidential means to the organization Response Policy A security policy should provide for a planned response in the event of a security breach. The response policy should identify the members of a response team, all of whom should clearly understand the the security policy, risks, and measures in place. Some of the roles concerned could include… Dispatcher – the person on call who first notices the breach Manager – the person who coordinates the resources necessary to solve the problem Technical Support Specialist – the person who focuses on solving the problem Public relations specialist – the person who acts as the official spokesperson for the organization Physical Security An important element in network security is restricting physical access to its components. There are various techniques for this including locking doors, security people at access points etc. You should identify the following… Which rooms contain critical systems or data and must be secured Through what means might intruders gain access to these rooms How and to what extent are authorized personnel granted access to these rooms Are authentication methods such as ID cards easy to forge etc. Security in Network Design The optimal way to prevent external security breaches from affecting you LAN is not to connect your LAN to the outside world at all. The next best protection is to restrict access at every point where your LAN connects to the rest of the world. Router Access List – can be used to filter or decline access to a portion of a network for certain devices. Intrusion Detection and Prevention While denying someone access to a section of the network is good, it is better to be able to detect when an attempt has been made and notify security personnel. This can be done using IDS (intrusion detection system) software. One drawback of IDS software is it can detect false positives – i.e. an authorized person who has forgotten his password attempts to logon. Firewalls A firewall is a specialized device, or a computer installed with specialized software, that selectively filters or blocks traffic between networks. A firewall typically involves a combination of hardware and software and may reside between two interconnected private networks. The simplest form of a firewall is a packet filtering firewall, which is a router that examines the header of every packet of data it receives to determine whether that type of packet is authorized to continue to its destination or not. Firewalls can block traffic in and out of a LAN. NOS (Network Operating System) Security Regardless of the operating system, generally every network administrator can implement basic security by restricting what users are authorized to do on a network. Some of the restrictions include things related to Logons – place, time of day, total time logged in, etc Passwords – length, characters used, etc Encryption Encryption is the use of an algorithm to scramble data into a format that can be read only by reversing the algorithm. The purpose of encryption is to keep information private. Many forms of encryption exist and new ways of cracking encryption are continually being invented. The following are some categories of encryption… Key Encryption PGP (Pretty Good Privacy) SSL (Secure Sockets Layer) SSH (Secure Shell) SCP (Secure CoPy) SFTP (Secure File Transfer Protocol) IPSec (Internet Protocol Security) For a detailed explanation on each section refer to pages 596 to 604 of textbook Authentication Protocols Authentication protocols are the rules that computers follow to accomplish authentication. Several types exist and the following are some of the common authentication protocols… RADIUS and TACACS PAP (Password Authentication Protocol) CHAP and MS-CHAP EAP (Extensible Authentication Protocol) 802.1x (EAPoL) Kerberos Wireless Network Security Wireless transmissions are particularly susceptible to eavesdropping. The following are two wireless network security protocols WEP WPA

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• configure a Cisco ASA to use MS-CHAP v2 for RADIUS authentication

  - by DrStalker

  Cisco ASA5505 8.2(2) Windows 2003 AD server We want to configure our ASA (10.1.1.1) to authenticate remote VPN users through RADIUS on the Windows AD controller (10.1.1.200) We have the following entry on the ASA: aaa-server SYSCON-RADIUS protocol radius aaa-server SYSCON-RADIUS (inside) host 10.1.1.200 key ***** radius-common-pw ***** When I test a login using the account COMPANY\username I see the users credentials are correct in the security log, but I get the following in the windows system logs: User COMPANY\myusername was denied access. Fully-Qualified-User-Name = company.com/CorpUsers/AU/My Name NAS-IP-Address = 10.1.1.1 NAS-Identifier = <not present> Called-Station-Identifier = <not present> Calling-Station-Identifier = <not present> Client-Friendly-Name = ASA5510 Client-IP-Address = 10.1.1.1 NAS-Port-Type = Virtual NAS-Port = 7 Proxy-Policy-Name = Use Windows authentication for all users Authentication-Provider = Windows Authentication-Server = <undetermined> Policy-Name = VPN Authentication Authentication-Type = PAP EAP-Type = <undetermined> Reason-Code = 66 Reason = The user attempted to use an authentication method that is not enabled on the matching remote access policy. My assumption is that the ASA is using PAP authentication, instead of MS-CHAP v2; the credentials are confirmed, the proper Remote Access Policy is being used, but this policy is set to only allow MS-CHAP2. What do we need to do on the ASA to make it us MS-CHAP v2? In the ADSM GUI The "Microsoft CHAP v2 compatible" tickbox is enabled, but I don't know what this corresponds to in the config.

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• The Alexandria Project, Chap. 13: Desperately Seeking Adversego

  <b>Standards Blog:</b> "With Frank on the run, Carl had just two responsibilities: protecting Frank's daughter Marla without her knowledge, which was a pretty ho-hum job, and protecting Frank, which at the moment was impossible."

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• Computer Networks UNISA - Chap 15 &ndash; Network Management

  - by MarkPearl

  After reading this section you should be able to Understand network management and the importance of documentation, baseline measurements, policies, and regulations to assess and maintain a network’s health. Manage a network’s performance using SNMP-based network management software, system and event logs, and traffic-shaping techniques Identify the reasons for and elements of an asset managements system Plan and follow regular hardware and software maintenance routines Fundamentals of Network Management Network management refers to the assessment, monitoring, and maintenance of all aspects of a network including checking for hardware faults, ensuring high QoS, maintaining records of network assets, etc. Scope of network management differs depending on the size and requirements of the network. All sub topics of network management share the goals of enhancing the efficiency and performance while preventing costly downtime or loss. Documentation The way documentation is stored may vary, but to adequately manage a network one should at least record the following… Physical topology (types of LAN and WAN topologies – ring, star, hybrid) Access method (does it use Ethernet 802.3, token ring, etc.) Protocols Devices (Switches, routers, etc) Operating Systems Applications Configurations (What version of operating system and config files for serve / client software) Baseline Measurements A baseline is a report of the network’s current state of operation. Baseline measurements might include the utilization rate for your network backbone, number of users logged on per day, etc. Baseline measurements allow you to compare future performance increases or decreases caused by network changes or events with past network performance. Obtaining baseline measurements is the only way to know for certain whether a pattern of usage has changed, or whether a network upgrade has made a difference. There are various tools available for measuring baseline performance on a network. Policies, Procedures, and Regulations Following rules helps limit chaos, confusion, and possibly downtime. The following policies and procedures and regulations make for sound network management. Media installations and management (includes designing physical layout of cable, etc.) Network addressing policies (includes choosing and applying a an addressing scheme) Resource sharing and naming conventions (includes rules for logon ID’s) Security related policies Troubleshooting procedures Backup and disaster recovery procedures In addition to internal policies, a network manager must consider external regulatory rules. Fault and Performance Management After documenting every aspect of your network and following policies and best practices, you are ready to asses you networks status on an on going basis. This process includes both performance management and fault management. Network Management Software To accomplish both fault and performance management, organizations often use enterprise-wide network management software. There various software packages that do this, each collect data from multiple networked devices at regular intervals, in a process called polling. Each managed device runs a network management agent. So as not to affect the performance of a device while collecting information, agents do not demand significant processing resources. The definition of a managed devices and their data are collected in a MIB (Management Information Base). Agents communicate information about managed devices via any of several application layer protocols. On modern networks most agents use SNMP which is part of the TCP/IP suite and typically runs over UDP on port 161. Because of the flexibility and sophisticated network management applications are a challenge to configure and fine-tune. One needs to be careful to only collect relevant information and not cause performance issues (i.e. pinging a device every 5 seconds can be a problem with thousands of devices). MRTG (Multi Router Traffic Grapher) is a simple command line utility that uses SNMP to poll devices and collects data in a log file. MRTG can be used with Windows, UNIX and Linux. System and Event Logs Virtually every condition recognized by an operating system can be recorded. This is typically done using event logs. In Windows there is a GUI event log viewer. Similar information is recorded in UNIX and Linux in a system log. Much of the information collected in event logs and syslog files does not point to a problem, even if it is marked with a warning so it is important to filter your logs appropriately to reduce the noise. Traffic Shaping When a network must handle high volumes of network traffic, users benefit from performance management technique called traffic shaping. Traffic shaping involves manipulating certain characteristics of packets, data streams, or connections to manage the type and amount of traffic traversing a network or interface at any moment. Its goals are to assure timely delivery of the most important traffic while offering the best possible performance for all users. Several types of traffic prioritization exist including prioritizing traffic according to any of the following characteristics… Protocol IP address User group DiffServr VLAN tag in a Data Link layer frame Service or application Caching In addition to traffic shaping, a network or host might use caching to improve performance. Caching is the local storage of frequently needed files that would otherwise be obtained from an external source. By keeping files close to the requester, caching allows the user to access those files quickly. The most common type of caching is Web caching, in which Web pages are stored locally. To an ISP, caching is much more than just convenience. It prevents a significant volume of WAN traffic, thus improving performance and saving money. Asset Management Another key component in managing networks is identifying and tracking its hardware. This is called asset management. The first step to asset management is to take an inventory of each node on the network. You will also want to keep records of every piece of software purchased by your organization. Asset management simplifies maintaining and upgrading the network chiefly because you know what the system includes. In addition, asset management provides network administrators with information about the costs and benefits of certain types of hardware or software. Change Management Networks are always in a stage of flux with various aspects including… Software changes and patches Client Upgrades Shared Application Upgrades NOS Upgrades Hardware and Physical Plant Changes Cabling Upgrades Backbone Upgrades For a detailed explanation on each of these read the textbook (Page 750 – 761)

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• Computer Networks UNISA - Chap 8 &ndash; Wireless Networking

  - by MarkPearl

  After reading this section you should be able to Explain how nodes exchange wireless signals Identify potential obstacles to successful transmission and their repercussions, such as interference and reflection Understand WLAN architecture Specify the characteristics of popular WLAN transmission methods including 802.11 a/b/g/n Install and configure wireless access points and their clients Describe wireless MAN and WAN technologies, including 802.16 and satellite communications The Wireless Spectrum All wireless signals are carried through the air by electromagnetic waves. The wireless spectrum is a continuum of the electromagnetic waves used for data and voice communication. The wireless spectrum falls between 9KHZ and 300 GHZ. Characteristics of Wireless Transmission Antennas Each type of wireless service requires an antenna specifically designed for that service. The service’s specification determine the antenna’s power output, frequency, and radiation pattern. A directional antenna issues wireless signals along a single direction. An omnidirectional antenna issues and receives wireless signals with equal strength and clarity in all directions The geographical area that an antenna or wireless system can reach is known as its range Signal Propagation LOS (line of sight) uses the least amount of energy and results in the reception of the clearest possible signal. When there is an obstacle in the way, the signal may… pass through the object or be obsrobed by the object or may be subject to reflection, diffraction or scattering. Reflection – waves encounter an object and bounces off it. Diffraction – signal splits into secondary waves when it encounters an obstruction Scattering – is the diffusion or the reflection in multiple different directions of a signal Signal Degradation Fading occurs as a signal hits various objects. Because of fading, the strength of the signal that reaches the receiver is lower than the transmitted signal strength. The further a signal moves from its source, the weaker it gets (this is called attenuation) Signals are also affected by noise – the electromagnetic interference) Interference can distort and weaken a wireless signal in the same way that noise distorts and weakens a wired signal. Frequency Ranges Older wireless devices used the 2.4 GHZ band to send and receive signals. This had 11 communication channels that are unlicensed. Newer wireless devices can also use the 5 GHZ band which has 24 unlicensed bands Narrowband, Broadband, and Spread Spectrum Signals Narrowband – a transmitter concentrates the signal energy at a single frequency or in a very small range of frequencies Broadband – uses a relatively wide band of the wireless spectrum and offers higher throughputs than narrowband technologies The use of multiple frequencies to transmit a signal is known as spread-spectrum technology. In other words a signal never stays continuously within one frequency range during its transmission. One specific implementation of spread spectrum is FHSS (frequency hoping spread spectrum). Another type is known as DSS (direct sequence spread spectrum) Fixed vs. Mobile Each type of wireless communication falls into one of two categories Fixed – the location of the transmitted and receiver do not move (results in energy saved because weaker signal strength is possible with directional antennas) Mobile – the location can change WLAN (Wireless LAN) Architecture There are two main types of arrangements Adhoc – data is sent directly between devices – good for small local devices Infrastructure mode – a wireless access point is placed centrally, that all devices connect with 802.11 WLANs The most popular wireless standards used on contemporary LANs are those developed by IEEE’s 802.11 committee. Over the years several distinct standards related to wireless networking have been released. Four of the best known standards are also referred to as Wi-Fi. They are…. 802.11b 802.11a 802.11g 802.11n These four standards share many characteristics. i.e. All 4 use half duplex signalling Follow the same access method Access Method 802.11 standards specify the use of CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) to access a shared medium. Using CSMA/CA before a station begins to send data on an 802.11 network, it checks for existing wireless transmissions. If the source node detects no transmission activity on the network, it waits a brief period of time and then sends its transmission. If the source does detect activity, it waits a brief period of time before checking again. The destination node receives the transmission and, after verifying its accuracy, issues an acknowledgement (ACT) packet to the source. If the source receives the ACK it assumes the transmission was successful, – if it does not receive an ACK it assumes the transmission failed and sends it again. Association Two types of scanning… Active – station transmits a special frame, known as a prove, on all available channels within its frequency range. When an access point finds the probe frame, it issues a probe response. Passive – wireless station listens on all channels within its frequency range for a special signal, known as a beacon frame, issued from an access point – the beacon frame contains information necessary to connect to the point. Re-association occurs when a mobile user moves out of one access point’s range and into the range of another. Frames Read page 378 – 381 about frames and specific 802.11 protocols Bluetooth Networks Sony Ericson originally invented the Bluetooth technology in the early 1990s. In 1998 other manufacturers joined Ericsson in the Special Interest Group (SIG) whose aim was to refine and standardize the technology. Bluetooth was designed to be used on small networks composed of personal communications devices. It has become popular wireless technology for communicating among cellular telephones, phone headsets, etc. Wireless WANs and Internet Access Refer to pages 396 – 402 of the textbook for details.

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• PPTP VPN Not Working - Peer failed CHAP authentication, PTY read or GRE write failed

  - by armani

  Brand-new install of CentOS 6.3. Followed this guide: http://www.members.optushome.com.au/~wskwok/poptop_ads_howto_1.htm And I got PPTPd running [v1.3.4]. I got the VPN to authenticate users against our Active Directory using winbind, smb, etc. All my tests to see if I'm still authenticated to the AD server pass ["kinit -V [email protected]", "smbclient", "wbinfo -t"]. VPN users were able to connect for like . . . an hour. I tried connecting from my Android phone using domain credentials and saw that I got an IP allocated for internal VPN users [which I've since changed the range, but even setting it back to the initial doesn't work]. Ever since then, no matter what settings I try, I pretty much consistently get this in my /var/log/messages [and the VPN client fails]: [root@vpn2 ~]# tail /var/log/messages Aug 31 15:57:22 vpn2 pppd[18386]: pppd 2.4.5 started by root, uid 0 Aug 31 15:57:22 vpn2 pppd[18386]: Using interface ppp0 Aug 31 15:57:22 vpn2 pppd[18386]: Connect: ppp0 <--> /dev/pts/1 Aug 31 15:57:22 vpn2 pptpd[18385]: GRE: Bad checksum from pppd. Aug 31 15:57:24 vpn2 pppd[18386]: Peer armaniadm failed CHAP authentication Aug 31 15:57:24 vpn2 pppd[18386]: Connection terminated. Aug 31 15:57:24 vpn2 pppd[18386]: Exit. Aug 31 15:57:24 vpn2 pptpd[18385]: GRE: read(fd=6,buffer=8059660,len=8196) from PTY failed: status = -1 error = Input/output error, usually caused by unexpected termination of pppd, check option syntax and pppd logs Aug 31 15:57:24 vpn2 pptpd[18385]: CTRL: PTY read or GRE write failed (pty,gre)=(6,7) Aug 31 15:57:24 vpn2 pptpd[18385]: CTRL: Client 208.54.86.242 control connection finished Now before you go blaming the firewall [all other forum posts I find seem to go there], this VPN server is on our DMZ network. We're using a Juniper SSG-5 Gateway, and I've assigned a WAN IP to the VPN box itself, zoned into the DMZ zone. Then, I have full "Any IP / Any Protocol" open traffic rules between DMZ<--Untrust Zone, and DMZ<--Trust Zone. I'll limit this later to just the authenticating traffic it needs, but for now I think we can rule out the firewall blocking anything. Here's my /etc/pptpd.conf [omitting comments]: option /etc/ppp/options.pptpd logwtmp localip [EXTERNAL_IP_ADDRESS] remoteip [ANOTHER_EXTERNAL_IP_ADDRESS, AND HAVE TRIED AN ARBITRARY GROUP LIKE 5.5.0.0-100] Here's my /etc/ppp/options.pptpd.conf [omitting comments]: name pptpd refuse-pap refuse-chap refuse-mschap require-mschap-v2 require-mppe-128 ms-dns 192.168.200.42 # This is our internal domain controller ms-wins 192.168.200.42 proxyarp lock nobsdcomp novj novjccomp nologfd auth nodefaultroute plugin winbind.so ntlm_auth-helper "/usr/bin/ntlm_auth --helper-protocol=ntlm-server-1" Any help is GREATLY appreciated. I can give you any more info you need to know, and it's a new test server, so I can perform any tests/reboots required to get it up and going. Thanks a ton.

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• Mpd as pppoe server with authorisation by freeradius2

  - by Korjavin Ivan

  I install freeradius2, add to raddb/users: test Cleartext-Password := "test1" Service-Type = Framed-User, Framed-Protocol = PPP, Framed-IP-Address = 10.36.0.2, Framed-IP-Netmask = 255.255.255.0, start radiusd, and check auth: radtest test test1 127.0.0.1 1002 testing123 Sending Access-Request of id 199 to 127.0.0.1 port 1812 User-Name = "test" User-Password = "test1" NAS-IP-Address = 127.0.0.1 NAS-Port = 1002 Message-Authenticator = 0x00000000000000000000000000000000 rad_recv: Access-Accept packet from host 127.0.0.1 port 1812, id=199, length=44 Service-Type = Framed-User Framed-Protocol = PPP Framed-IP-Address = 10.36.0.2 Framed-IP-Netmask = 255.255.255.0 Works fine. Next step. Add to mpd.conf: radius: set auth disable internal set auth max-logins 1 CI set auth enable radius-auth set radius timeout 90 set radius retries 2 set radius server 127.0.0.1 testing123 1812 1813 set radius me 127.0.0.1 create link template L pppoe set link action bundle B set link max-children 1000 set link no multilink set link no shortseq set link no pap chap-md5 chap-msv1 chap-msv2 set link enable chap set pppoe acname Internet load radius create link template em1 L set pppoe iface em1 set link enable incoming And trying to connect, auth failed, here is mpd log: mpd: [em1-2] LCP: auth: peer wants nothing, I want CHAP mpd: [em1-2] CHAP: sending CHALLENGE #1 len: 21 mpd: [em1-2] LCP: LayerUp mpd: [em1-2] CHAP: rec'd RESPONSE #1 len: 58 mpd: [em1-2] Name: "test" mpd: [em1-2] AUTH: Trying RADIUS mpd: [em1-2] RADIUS: Authenticating user 'test' mpd: [em1-2] RADIUS: Rec'd RAD_ACCESS_REJECT for user 'test' mpd: [em1-2] AUTH: RADIUS returned: failed mpd: [em1-2] AUTH: ran out of backends mpd: [em1-2] CHAP: Auth return status: failed mpd: [em1-2] CHAP: Reply message: ^AE=691 R=1 mpd: [em1-2] CHAP: sending FAILURE #1 len: 14 mpd: [em1-2] LCP: authorization failed Then i start freeradius as radiusd -fX, and get this log: rad_recv: Access-Request packet from host 127.0.0.1 port 46400, id=223, length=282 NAS-Identifier = "rubin.svyaz-nt.ru" NAS-IP-Address = 127.0.0.1 Message-Authenticator = 0x14d36639bed8074ec2988118125367ea Acct-Session-Id = "815965-em1-2" NAS-Port = 2 NAS-Port-Type = Ethernet Service-Type = Framed-User Framed-Protocol = PPP Calling-Station-Id = "00e05290b3e3 / 00:e0:52:90:b3:e3 / em1" NAS-Port-Id = "em1" Vendor-12341-Attr-12 = 0x656d312d32 Tunnel-Medium-Type:0 = IEEE-802 Tunnel-Client-Endpoint:0 = "00:e0:52:90:b3:e3" User-Name = "test" MS-CHAP-Challenge = 0xbb1e68d5bbc30f228725a133877de83e MS-CHAP2-Response = 0x010088746ae65b68e435e9d045ad6f9569b60000000000000000b56991b4f20704cb6c68e5982eec5e98a7f4b470c109c1b9 # Executing section authorize from file /usr/local/etc/raddb/sites-enabled/default +- entering group authorize {...} ++[preprocess] returns ok ++[chap] returns noop [mschap] Found MS-CHAP attributes. Setting 'Auth-Type = mschap' ++[mschap] returns ok [eap] No EAP-Message, not doing EAP ++[eap] returns noop [files] users: Matched entry DEFAULT at line 172 ++[files] returns ok Found Auth-Type = MSCHAP # Executing group from file /usr/local/etc/raddb/sites-enabled/default +- entering group MS-CHAP {...} [mschap] No Cleartext-Password configured. Cannot create LM-Password. [mschap] No Cleartext-Password configured. Cannot create NT-Password. [mschap] Creating challenge hash with username: test [mschap] Client is using MS-CHAPv2 for test, we need NT-Password [mschap] FAILED: No NT/LM-Password. Cannot perform authentication. [mschap] FAILED: MS-CHAP2-Response is incorrect ++[mschap] returns reject Failed to authenticate the user. Login incorrect: [test] (from client localhost port 2 cli 00e05290b3e3 / 00:e0:52:90:b3:e3 / em1) Using Post-Auth-Type REJECT # Executing group from file /usr/local/etc/raddb/sites-enabled/default +- entering group REJECT {...} [attr_filter.access_reject] expand: %{User-Name} -> test attr_filter: Matched entry DEFAULT at line 11 ++[attr_filter.access_reject] returns updated Delaying reject of request 2 for 1 seconds Going to the next request Waking up in 0.9 seconds. Sending delayed reject for request 2 Sending Access-Reject of id 223 to 127.0.0.1 port 46400 MS-CHAP-Error = "\001E=691 R=1" Why i have error "[mschap] No Cleartext-Password configured. Cannot create LM-Password." ? I define cleartext-password in users. I check raddb/sites-enabled/default authorize { chap mschap eap { ok = return } files } looks ok for me. Whats wrong with mpd/chap/radius ?

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• Software developer needs Validation for VA Chap 31 to purchase Macbook Pro vs. PC [closed]

  - by David

  I am currently attending college with a path of software development and working towards my BS thanks to VA Chap 31. My old original Macbook Pro is near dead and no longer upgradable on the software or hardware side. The VA has offered to purchase a PC laptop for me (Because my syllabi says computer required), but I do not want to go backwards. I have a lot invested in OS X software and Mac peripherals, not to mention I prefer to program in an Apple environment. PC vs. Mac costs are so drastically different that I must validate my request for a new Macbook Pro. In my request to the VA, I stated the above and some other topics but they requested more validation. Can anyone recommend issues, reasons, etc. to help me validate this purchase by the VA for school? Thanks in advance for your help, David

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• Cisco: unable to negotiate IP using IPCP with Windows server

  - by lnk

  I am connecting to Windows server using PPP (for vpn), I establish connection but server does not respond me for my address requests: *Mar 23 00:40:06.055: Vi1 MS-CHAP-V2: I CHALLENGE id 0 len 25 from "MSDC" *Mar 23 00:40:06.063: Vi1 MS CHAP V2: Using hostname from interface CHAP *Mar 23 00:40:06.063: Vi1 MS CHAP V2: Using password from interface CHAP *Mar 23 00:40:06.067: Vi1 MS-CHAP-V2: O RESPONSE id 0 len 69 from "XXX" *Mar 23 00:40:06.087: Vi1 PPP: I pkt type 0xC223, datagramsize 50 link[ppp] *Mar 23 00:40:06.087: Vi1 MS-CHAP-V2: I SUCCESS id 0 len 46 msg is "S=XXX" *Mar 23 00:40:06.087: Vi1 MS CHAP V2 No Password found for : XXX *Mar 23 00:40:06.091: Vi1 MS CHAP V2 Check AuthenticatorResponse Success for : XXX *Mar 23 00:40:06.091: Vi1 IPCP: O CONFREQ [Closed] id 1 len 20 *Mar 23 00:40:06.091: Vi1 IPCP: VSO OUI 0x00000C kind 1 (0x000A00000C0100000000) *Mar 23 00:40:06.091: Vi1 IPCP: Address 0.0.0.0 (0x030600000000) *Mar 23 00:40:07.091: %LINEPROTO-5-UPDOWN: Line protocol on Interface Virtual-Access1, changed state to up *Mar 23 00:40:07.091: Vi1 LCP: O ECHOREQ [Open] id 1 len 12 magic 0x194CAFCF *Mar 23 00:40:07.103: Vi1 LCP-FS: I ECHOREP [Open] id 1 len 12 magic 0x361B62E5 *Mar 23 00:40:07.103: Vi1 LCP-FS: Received id 1, sent id 1, line up *Mar 23 00:40:08.083: Vi1 IPCP: TIMEout: State REQsent *Mar 23 00:40:08.083: Vi1 IPCP: O CONFREQ [REQsent] id 2 len 20 *Mar 23 00:40:08.083: Vi1 IPCP: VSO OUI 0x00000C kind 1 (0x000A00000C0100000000) *Mar 23 00:40:08.083: Vi1 IPCP: Address 0.0.0.0 (0x030600000000) *Mar 23 00:40:10.099: Vi1 IPCP: TIMEout: State REQsent *Mar 23 00:40:10.099: Vi1 IPCP: O CONFREQ [REQsent] id 3 len 20 *Mar 23 00:40:10.099: Vi1 IPCP: VSO OUI 0x00000C kind 1 (0x000A00000C0100000000) *Mar 23 00:40:10.099: Vi1 IPCP: Address 0.0.0.0 (0x030600000000) *Mar 23 00:40:12.115: Vi1 IPCP: TIMEout: State REQsent *Mar 23 00:40:12.115: Vi1 IPCP: O CONFREQ [REQsent] id 4 len 20 *Mar 23 00:40:12.115: Vi1 IPCP: VSO OUI 0x00000C kind 1 (0x000A00000C0100000000) *Mar 23 00:40:12.115: Vi1 IPCP: Address 0.0.0.0 (0x030600000000) *Mar 23 00:40:12.211: Vi1 LCP: O ECHOREQ [Open] id 2 len 12 magic 0x194CAFCF *Mar 23 00:40:12.219: Vi1 LCP-FS: I ECHOREP [Open] id 2 len 12 magic 0x361B62E5 *Mar 23 00:40:12.219: Vi1 LCP-FS: Received id 2, sent id 2, line up *Mar 23 00:40:14.131: Vi1 IPCP: TIMEout: State REQsent *Mar 23 00:40:14.131: Vi1 IPCP: O CONFREQ [REQsent] id 5 len 20 *Mar 23 00:40:14.131: Vi1 IPCP: VSO OUI 0x00000C kind 1 (0x000A00000C0100000000) *Mar 23 00:40:14.131: Vi1 IPCP: Address 0.0.0.0 (0x030600000000) *Mar 23 00:40:16.147: Vi1 IPCP: TIMEout: State REQsent *Mar 23 00:40:16.147: Vi1 IPCP: O CONFREQ [REQsent] id 6 len 20 *Mar 23 00:40:16.147: Vi1 IPCP: VSO OUI 0x00000C kind 1 (0x000A00000C0100000000) *Mar 23 00:40:16.147: Vi1 IPCP: Address 0.0.0.0 (0x030600000000) *Mar 23 00:40:17.331: Vi1 LCP: O ECHOREQ [Open] id 3 len 12 magic 0x194CAFCF *Mar 23 00:40:17.343: Vi1 LCP-FS: I ECHOREP [Open] id 3 len 12 magic 0x361B62E5 *Mar 23 00:40:17.343: Vi1 LCP-FS: Received id 3, sent id 3, line up You see: My router asks for address, but only keepalives are on line. But the same server works with windows client!! ! version 12.4 no service pad service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption service internal ! hostname Router ! boot-start-marker boot-end-marker ! ! no aaa new-model ! resource policy ! ip subnet-zero ! ! ip cef vpdn enable ! vpdn-group pptp request-dialin protocol pptp pool-member 1 initiate-to ip XXXX ! ! ! ! ! ! ! bridge irb ! ! interface ATM0 no ip address shutdown no atm ilmi-keepalive dsl operating-mode auto ! interface FastEthernet0 ! interface FastEthernet1 ! interface FastEthernet2 ! interface FastEthernet3 ! interface Dot11Radio0 no ip address shutdown speed basic-1.0 basic-2.0 basic-5.5 6.0 9.0 basic-11.0 12.0 18.0 24.0 36.0 48.0 54.0 station-role root ! interface Vlan1 no ip address bridge-group 1 ! interface Dialer0 ip address negotiated encapsulation ppp dialer pool 1 dialer idle-timeout 0 dialer string XXX dialer persistent dialer vpdn dialer-group 1 keepalive 5 3 no cdp enable ppp authentication ms-chap-v2 optional ppp eap refuse ppp chap hostname XXX ppp chap password 0 XXX ppp ipcp mask request ppp ipcp ignore-map ppp ipcp address accept ! interface BVI1 mac-address XXX.XXX.XXX ip address dhcp ! ip classless ip route 172.0.0.0 255.0.0.0 Dialer0 ! no ip http server no ip http secure-server ! dialer-list 1 protocol ip permit ! control-plane ! bridge 1 protocol vlan-bridge bridge 1 route ip ! line con 0 no modem enable line aux 0 line vty 0 4 login ! scheduler max-task-time 5000 end

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• Organizations &amp; Architecture UNISA Studies &ndash; Chap 7

  - by MarkPearl

  Learning Outcomes Name different device categories Discuss the functions and structure of I/.O modules Describe the principles of Programmed I/O Describe the principles of Interrupt-driven I/O Describe the principles of DMA Discuss the evolution characteristic of I/O channels Describe different types of I/O interface Explain the principles of point-to-point and multipoint configurations Discuss the way in which a FireWire serial bus functions Discuss the principles of InfiniBand architecture External Devices An external device attaches to the computer by a link to an I/O module. The link is used to exchange control, status, and data between the I/O module and the external device. External devices can be classified into 3 categories… Human readable – e.g. video display Machine readable – e.g. magnetic disk Communications – e.g. wifi card I/O Modules An I/O module has two major functions… Interface to the processor and memory via the system bus or central switch Interface to one or more peripheral devices by tailored data links Module Functions The major functions or requirements for an I/O module fall into the following categories… Control and timing Processor communication Device communication Data buffering Error detection I/O function includes a control and timing requirement, to coordinate the flow of traffic between internal resources and external devices. Processor communication involves the following… Command decoding Data Status reporting Address recognition The I/O device must be able to perform device communication. This communication involves commands, status information, and data. An essential task of an I/O module is data buffering due to the relative slow speeds of most external devices. An I/O module is often responsible for error detection and for subsequently reporting errors to the processor. I/O Module Structure An I/O module functions to allow the processor to view a wide range of devices in a simple minded way. The I/O module may hide the details of timing, formats, and the electro mechanics of an external device so that the processor can function in terms of simple reads and write commands. An I/O channel/processor is an I/O module that takes on most of the detailed processing burden, presenting a high-level interface to the processor. There are 3 techniques are possible for I/O operations Programmed I/O Interrupt[t I/O DMA Access Programmed I/O When a processor is executing a program and encounters an instruction relating to I/O it executes that instruction by issuing a command to the appropriate I/O module. With programmed I/O, the I/O module will perform the requested action and then set the appropriate bits in the I/O status register. The I/O module takes no further actions to alert the processor. I/O Commands To execute an I/O related instruction, the processor issues an address, specifying the particular I/O module and external device, and an I/O command. There are four types of I/O commands that an I/O module may receive when it is addressed by a processor… Control – used to activate a peripheral and tell it what to do Test – Used to test various status conditions associated with an I/O module and its peripherals Read – Causes the I/O module to obtain an item of data from the peripheral and place it in an internal buffer Write – Causes the I/O module to take an item of data form the data bus and subsequently transmit that data item to the peripheral The main disadvantage of this technique is it is a time consuming process that keeps the processor busy needlessly I/O Instructions With programmed I/O there is a close correspondence between the I/O related instructions that the processor fetches from memory and the I/O commands that the processor issues to an I/O module to execute the instructions. Typically there will be many I/O devices connected through I/O modules to the system – each device is given a unique identifier or address – when the processor issues an I/O command, the command contains the address of the address of the desired device, thus each I/O module must interpret the address lines to determine if the command is for itself. When the processor, main memory and I/O share a common bus, two modes of addressing are possible… Memory mapped I/O Isolated I/O (for a detailed explanation read page 245 of book) The advantage of memory mapped I/O over isolated I/O is that it has a large repertoire of instructions that can be used, allowing more efficient programming. The disadvantage of memory mapped I/O over isolated I/O is that valuable memory address space is sued up. Interrupts driven I/O Interrupt driven I/O works as follows… The processor issues an I/O command to a module and then goes on to do some other useful work The I/O module will then interrupts the processor to request service when is is ready to exchange data with the processor The processor then executes the data transfer and then resumes its former processing Interrupt Processing The occurrence of an interrupt triggers a number of events, both in the processor hardware and in software. When an I/O device completes an I/O operations the following sequence of hardware events occurs… The device issues an interrupt signal to the processor The processor finishes execution of the current instruction before responding to the interrupt The processor tests for an interrupt – determines that there is one – and sends an acknowledgement signal to the device that issues the interrupt. The acknowledgement allows the device to remove its interrupt signal The processor now needs to prepare to transfer control to the interrupt routine. To begin, it needs to save information needed to resume the current program at the point of interrupt. The minimum information required is the status of the processor and the location of the next instruction to be executed. The processor now loads the program counter with the entry location of the interrupt-handling program that will respond to this interrupt. It also saves the values of the process registers because the Interrupt operation may modify these The interrupt handler processes the interrupt – this includes examination of status information relating to the I/O operation or other event that caused an interrupt When interrupt processing is complete, the saved register values are retrieved from the stack and restored to the registers Finally, the PSW and program counter values from the stack are restored. Design Issues Two design issues arise in implementing interrupt I/O Because there will be multiple I/O modules, how does the processor determine which device issued the interrupt? If multiple interrupts have occurred, how does the processor decide which one to process? Addressing device recognition, 4 general categories of techniques are in common use… Multiple interrupt lines Software poll Daisy chain Bus arbitration For a detailed explanation of these approaches read page 250 of the textbook. Interrupt driven I/O while more efficient than simple programmed I/O still requires the active intervention of the processor to transfer data between memory and an I/O module, and any data transfer must traverse a path through the processor. Thus is suffers from two inherent drawbacks… The I/O transfer rate is limited by the speed with which the processor can test and service a device The processor is tied up in managing an I/O transfer; a number of instructions must be executed for each I/O transfer Direct Memory Access When large volumes of data are to be moved, an efficient technique is direct memory access (DMA) DMA Function DMA involves an additional module on the system bus. The DMA module is capable of mimicking the processor and taking over control of the system from the processor. It needs to do this to transfer data to and from memory over the system bus. DMA must the bus only when the processor does not need it, or it must force the processor to suspend operation temporarily (most common – referred to as cycle stealing). When the processor wishes to read or write a block of data, it issues a command to the DMA module by sending to the DMA module the following information… Whether a read or write is requested using the read or write control line between the processor and the DMA module The address of the I/O device involved, communicated on the data lines The starting location in memory to read from or write to, communicated on the data lines and stored by the DMA module in its address register The number of words to be read or written, communicated via the data lines and stored in the data count register The processor then continues with other work, it delegates the I/O operation to the DMA module which transfers the entire block of data, one word at a time, directly to or from memory without going through the processor. When the transfer is complete, the DMA module sends an interrupt signal to the processor, this the processor is involved only at the beginning and end of the transfer. I/O Channels and Processors Characteristics of I/O Channels As one proceeds along the evolutionary path, more and more of the I/O function is performed without CPU involvement. The I/O channel represents an extension of the DMA concept. An I/O channel ahs the ability to execute I/O instructions, which gives it complete control over I/O operations. In a computer system with such devices, the CPU does not execute I/O instructions – such instructions are stored in main memory to be executed by a special purpose processor in the I/O channel itself. Two types of I/O channels are common A selector channel controls multiple high-speed devices. A multiplexor channel can handle I/O with multiple characters as fast as possible to multiple devices. The external interface: FireWire and InfiniBand Types of Interfaces One major characteristic of the interface is whether it is serial or parallel parallel interface – there are multiple lines connecting the I/O module and the peripheral, and multiple bits are transferred simultaneously serial interface – there is only one line used to transmit data, and bits must be transmitted one at a time With new generation serial interfaces, parallel interfaces are becoming less common. In either case, the I/O module must engage in a dialogue with the peripheral. In general terms the dialog may look as follows… The I/O module sends a control signal requesting permission to send data The peripheral acknowledges the request The I/O module transfers data The peripheral acknowledges receipt of data For a detailed explanation of FireWire and InfiniBand technology read page 264 – 270 of the textbook

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• Organization &amp; Architecture UNISA Studies &ndash; Chap 5

  - by MarkPearl

  Learning Outcomes Describe the operation of a memory cell Explain the difference between DRAM and SRAM Discuss the different types of ROM Explain the concepts of a hard failure and a soft error respectively Describe SDRAM organization Semiconductor Main Memory The two traditional forms of RAM used in computers are DRAM and SRAM DRAM (Dynamic RAM) Divided into two technologies… Dynamic Static Dynamic RAM is made with cells that store data as charge on capacitors. The presence or absence of charge in a capacitor is interpreted as a binary 1 or 0. Because capacitors have natural tendency to discharge, dynamic RAM requires periodic charge refreshing to maintain data storage. The term dynamic refers to the tendency of the stored charge to leak away, even with power continuously applied. Although the DRAM cell is used to store a single bit (0 or 1), it is essentially an analogue device. The capacitor can store any charge value within a range, a threshold value determines whether the charge is interpreted as a 1 or 0. SRAM (Static RAM) SRAM is a digital device that uses the same logic elements used in the processor. In SRAM, binary values are stored using traditional flip flop logic configurations. SRAM will hold its data as along as power is supplied to it. Unlike DRAM, no refresh is required to retain data. SRAM vs. DRAM DRAM is simpler and smaller than SRAM. Thus it is more dense and less expensive than SRAM. The cost of the refreshing circuitry for DRAM needs to be considered, but if the machine requires a large amount of memory, DRAM turns out to be cheaper than SRAM. SRAMS are somewhat faster than DRAM, thus SRAM is generally used for cache memory and DRAM is used for main memory. Types of ROM Read Only Memory (ROM) contains a permanent pattern of data that cannot be changed. ROM is non volatile meaning no power source is required to maintain the bit values in memory. While it is possible to read a ROM, it is not possible to write new data into it. An important application of ROM is microprogramming, other applications include library subroutines for frequently wanted functions, System programs, Function tables. A ROM is created like any other integrated circuit chip, with the data actually wired into the chip as part of the fabrication process. To reduce costs of fabrication, we have PROMS. PROMS are… Written only once Non-volatile Written after fabrication Another variation of ROM is the read-mostly memory, which is useful for applications in which read operations are far more frequent than write operations, but for which non volatile storage is required. There are three common forms of read-mostly memory, namely… EPROM EEPROM Flash memory Error Correction Semiconductor memory is subject to errors, which can be classed into two categories… Hard failure – Permanent physical defect so that the memory cell or cells cannot reliably store data Soft failure – Random error that alters the contents of one or more memory cells without damaging the memory (common cause includes power supply issues, etc.) Most modern main memory systems include logic for both detecting and correcting errors. Error detection works as follows… When data is to be read into memory, a calculation is performed on the data to produce a code Both the code and the data are stored When the previously stored word is read out, the code is used to detect and possibly correct errors The error checking provides one of 3 possible results… No errors are detected – the fetched data bits are sent out An error is detected, and it is possible to correct the error. The data bits plus error correction bits are fed into a corrector, which produces a corrected set of bits to be sent out An error is detected, but it is not possible to correct it. This condition is reported Hamming Code See wiki for detailed explanation. We will probably need to know how to do a hemming code – refer to the textbook (pg. 188 – 189) Advanced DRAM organization One of the most critical system bottlenecks when using high-performance processors is the interface to main memory. This interface is the most important pathway in the entire computer system. The basic building block of main memory remains the DRAM chip. In recent years a number of enhancements to the basic DRAM architecture have been explored, and some of these are now on the market including… SDRAM (Synchronous DRAM) DDR-DRAM RDRAM SDRAM (Synchronous DRAM) SDRAM exchanges data with the processor synchronized to an external clock signal and running at the full speed of the processor/memory bus without imposing wait states. SDRAM employs a burst mode to eliminate the address setup time and row and column line precharge time after the first access In burst mode a series of data bits can be clocked out rapidly after the first bit has been accessed SDRAM has a multiple bank internal architecture that improves opportunities for on chip parallelism SDRAM performs best when it is transferring large blocks of data serially There is now an enhanced version of SDRAM known as double data rate SDRAM or DDR-SDRAM that overcomes the once-per-cycle limitation of SDRAM

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• The Alexandria Project, Chap. 11: Have I got an App for You!

  <b>Standards Blog:</b> "While CIA Agent Carl Cummings was being taught to heel, Frank was sitting at his kitchen table, tapping away at the cramped keyboard of a cheap netbook connected to a neighbor&#8217;s unsecured WiFi network. Even this was risky, he reminded himself, so this brief session would have to be his last until he moved on."

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• Computer Networks UNISA - Chap 14 &ndash; Insuring Integrity &amp; Availability

  - by MarkPearl

  After reading this section you should be able to Identify the characteristics of a network that keep data safe from loss or damage Protect an enterprise-wide network from viruses Explain network and system level fault tolerance techniques Discuss issues related to network backup and recovery strategies Describe the components of a useful disaster recovery plan and the options for disaster contingencies What are integrity and availability? Integrity – the soundness of a networks programs, data, services, devices, and connections Availability – How consistently and reliably a file or system can be accessed by authorized personnel A number of phenomena can compromise both integrity and availability including… security breaches natural disasters malicious intruders power flaws human error users etc Although you cannot predict every type of vulnerability, you can take measures to guard against the most damaging events. The following are some guidelines… Allow only network administrators to create or modify NOS and application system users. Monitor the network for unauthorized access or changes Record authorized system changes in a change management system’ Install redundant components Perform regular health checks on the network Check system performance, error logs, and the system log book regularly Keep backups Implement and enforce security and disaster recovery policies These are just some of the basics… Malware Malware refers to any program or piece of code designed to intrude upon or harm a system or its resources. Types of Malware… Boot sector viruses Macro viruses File infector viruses Worms Trojan Horse Network Viruses Bots Malware characteristics Some common characteristics of Malware include… Encryption Stealth Polymorphism Time dependence Malware Protection There are various tools available to protect you from malware called anti-malware software. These monitor your system for indications that a program is performing potential malware operations. A number of techniques are used to detect malware including… Signature Scanning Integrity Checking Monitoring unexpected file changes or virus like behaviours It is important to decide where anti-malware tools will be installed and find a balance between performance and protection. There are several general purpose malware policies that can be implemented to protect your network including… Every compute in an organization should be equipped with malware detection and cleaning software that regularly runs Users should not be allowed to alter or disable the anti-malware software Users should know what to do in case the anti-malware program detects a malware virus Users should be prohibited from installing any unauthorized software on their systems System wide alerts should be issued to network users notifying them if a serious malware virus has been detected. Fault Tolerance Besides guarding against malware, another key factor in maintaining the availability and integrity of data is fault tolerance. Fault tolerance is the ability for a system to continue performing despite an unexpected hardware or software malfunction. Fault tolerance can be realized in varying degrees, the optimal level of fault tolerance for a system depends on how critical its services and files are to productivity. Generally the more fault tolerant the system, the more expensive it is. The following describe some of the areas that need to be considered for fault tolerance. Environment (Temperature and humidity) Power Topology and Connectivity Servers Storage Power Typical power flaws include Surges – a brief increase in voltage due to lightening strikes, solar flares or some idiot at City Power Noise – Fluctuation in voltage levels caused by other devices on the network or electromagnetic interference Brownout – A sag in voltage for just a moment Blackout – A complete power loss The are various alternate power sources to consider including UPS’s and Generators. UPS’s are found in two categories… Standby UPS – provides continuous power when mains goes down (brief period of switching over) Online UPS – is online all the time and the device receives power from the UPS all the time (the UPS is charged continuously) Servers There are various techniques for fault tolerance with servers. Server mirroring is an option where one device or component duplicates the activities of another. It is generally an expensive process. Clustering is a fault tolerance technique that links multiple servers together to appear as a single server. They share processing and storage responsibilities and if one unit in the cluster goes down, another unit can be brought in to replace it. Storage There are various techniques available including the following… RAID Arrays NAS (Storage (Network Attached Storage) SANs (Storage Area Networks) Data Backup A backup is a copy of data or program files created for archiving or safekeeping. Many different options for backups exist with various media including… These vary in cost and speed. Optical Media Tape Backup External Disk Drives Network Backups Backup Strategy After selecting the appropriate tool for performing your servers backup, devise a backup strategy to guide you through performing reliable backups that provide maximum data protection. Questions that should be answered include… What data must be backed up At what time of day or night will the backups occur How will you verify the accuracy of the backups Where and for how long will backup media be stored Who will take responsibility for ensuring that backups occurred How long will you save backups Where will backup and recovery documentation be stored Different backup methods provide varying levels of certainty and corresponding labour cost. There are also different ways to determine which files should be backed up including… Full backup – all data on all servers is copied to storage media Incremental backup – Only data that has changed since the last full or incremental backup is copied to a storage medium Differential backup – Only data that has changed since the last backup is coped to a storage medium Disaster Recovery Disaster recovery is the process of restoring your critical functionality and data after an enterprise wide outage has occurred. A disaster recovery plan is for extreme scenarios (i.e. fire, line fault, etc). A cold site is a place were the computers, devices, and connectivity necessary to rebuild a network exist but they are not appropriately configured. A warm site is a place where the computers, devices, and connectivity necessary to rebuild a network exists with some appropriately configured devices. A hot site is a place where the computers, devices, and connectivity necessary to rebuild a network exists and all are appropriately configured.

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• Organization &amp; Architecture UNISA Studies &ndash; Chap 6

  - by MarkPearl

  Learning Outcomes Discuss the physical characteristics of magnetic disks Describe how data is organized and accessed on a magnetic disk Discuss the parameters that play a role in the performance of magnetic disks Describe different optical memory devices Magnetic Disk The way data is stored on and retried from magnetic disks Data is recorded on and later retrieved form the disk via a conducting coil named the head (in many systems there are two heads) The writ mechanism exploits the fact that electricity flowing through a coil produces a magnetic field. Electric pulses are sent to the write head, and the resulting magnetic patterns are recorded on the surface below with different patterns for positive and negative currents The physical characteristics of a magnetic disk   Summarize from book   The factors that play a role in the performance of a disk Seek time – the time it takes to position the head at the track Rotational delay / latency – the time it takes for the beginning of the sector to reach the head Access time – the sum of the seek time and rotational delay Transfer time – the time it takes to transfer data RAID The rate of improvement in secondary storage performance has been considerably less than the rate for processors and main memory. Thus secondary storage has become a bit of a bottleneck. RAID works on the concept that if one disk can be pushed so far, additional gains in performance are to be had by using multiple parallel components. Points to note about RAID… RAID is a set of physical disk drives viewed by the operating system as a single logical drive Data is distributed across the physical drives of an array in a scheme known as striping Redundant disk capacity is used to store parity information, which guarantees data recoverability in case of a disk failure (not supported by RAID 0 or RAID 1) Interesting to note that the increase in the number of drives, increases the probability of failure. To compensate for this decreased reliability RAID makes use of stored parity information that enables the recovery of data lost due to a disk failure.   The RAID scheme consists of 7 levels…   Category Level Description Disks Required Data Availability Large I/O Data Transfer Capacity Small I/O Request Rate Striping 0 Non Redundant N Lower than single disk Very high Very high for both read and write Mirroring 1 Mirrored 2N Higher than RAID 2 – 5 but lower than RAID 6 Higher than single disk Up to twice that of a signle disk for read Parallel Access 2 Redundant via Hamming Code N + m Much higher than single disk Highest of all listed alternatives Approximately twice that of a single disk Parallel Access 3 Bit interleaved parity N + 1 Much higher than single disk Highest of all listed alternatives Approximately twice that of a single disk Independent Access 4 Block interleaved parity N + 1 Much higher than single disk Similar to RAID 0 for read, significantly lower than single disk for write Similar to RAID 0 for read, significantly lower than single disk for write Independent Access 5 Block interleaved parity N + 1 Much higher than single disk Similar to RAID 0 for read, lower than single disk for write Similar to RAID 0 for read, generally  lower than single disk for write Independent Access 6 Block interleaved parity N + 2 Highest of all listed alternatives Similar to RAID 0 for read; lower than RAID 5 for write Similar to RAID 0 for read, significantly lower than RAID 5  for write   Read page 215 – 221 for detailed explanation on RAID levels Optical Memory There are a variety of optical-disk systems available. Read through the table on page 222 – 223 Some of the devices include… CD CD-ROM CD-R CD-RW DVD DVD-R DVD-RW Blue-Ray DVD Magnetic Tape Most modern systems use serial recording – data is lade out as a sequence of bits along each track. The typical recording used in serial is referred to as serpentine recording. In this technique when data is being recorded, the first set of bits is recorded along the whole length of the tape. When the end of the tape is reached the heads are repostioned to record a new track, and the tape is again recorded on its whole length, this time in the opposite direction. That process continued back and forth until the tape is full. To increase speed, the read-write head is capable of reading and writing a number of adjacent tracks simultaneously. Data is still recorded serially along individual tracks, but blocks in sequence are stored on adjacent tracks as suggested. A tape drive is a sequential access device. Magnetic tape was the first kind of secondary memory. It is still widely used as the lowest-cost, slowest speed member of the memory hierarchy.

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• Computer Networks UNISA - Chap 10 &ndash; In Depth TCP/IP Networking

  - by MarkPearl

  After reading this section you should be able to Understand methods of network design unique to TCP/IP networks, including subnetting, CIDR, and address translation Explain the differences between public and private TCP/IP networks Describe protocols used between mail clients and mail servers, including SMTP, POP3, and IMAP4 Employ multiple TCP/IP utilities for network discovery and troubleshooting Designing TCP/IP-Based Networks The following sections explain how network and host information in an IPv4 address can be manipulated to subdivide networks into smaller segments. Subnetting Subnetting separates a network into multiple logically defined segments, or subnets. Networks are commonly subnetted according to geographic locations, departmental boundaries, or technology types. A network administrator might separate traffic to accomplish the following… Enhance security Improve performance Simplify troubleshooting The challenges of Classful Addressing in IPv4 (No subnetting) The simplest type of IPv4 is known as classful addressing (which was the Class A, Class B & Class C network addresses). Classful addressing has the following limitations. Restriction in the number of usable IPv4 addresses (class C would be limited to 254 addresses) Difficult to separate traffic from various parts of a network Because of the above reasons, subnetting was introduced. IPv4 Subnet Masks Subnetting depends on the use of subnet masks to identify how a network is subdivided. A subnet mask indicates where network information is located in an IPv4 address. The 1 in a subnet mask indicates that corresponding bits in the IPv4 address contain network information (likewise 0 indicates the opposite) Each network class is associated with a default subnet mask… Class A = 255.0.0.0 Class B = 255.255.0.0 Class C = 255.255.255.0 An example of calculating  the network ID for a particular device with a subnet mask is shown below.. IP Address = 199.34.89.127 Subnet Mask = 255.255.255.0 Resultant Network ID = 199.34.89.0 IPv4 Subnetting Techniques Subnetting breaks the rules of classful IPv4 addressing. Read page 490 for a detailed explanation Calculating IPv4 Subnets Read page 491 – 494 for an explanation Important… Subnetting only applies to the devices internal to your network. Everything external looks at the class of the IP address instead of the subnet network ID. This way, traffic directed to your network externally still knows where to go, and once it has entered your internal network it can then be prioritized and segmented. CIDR (classless Interdomain Routing) CIDR is also known as classless routing or supernetting. In CIDR conventional network class distinctions do not exist, a subnet boundary can move to the left, therefore generating more usable IP addresses on your network. A subnet created by moving the subnet boundary to the left is known as a supernet. With CIDR also came new shorthand for denoting the position of subnet boundaries known as CIDR notation or slash notation. CIDR notation takes the form of the network ID followed by a forward slash (/) followed by the number of bits that are used for the extended network prefix. To take advantage of classless routing, your networks routers must be able to interpret IP addresses that don;t adhere to conventional network class parameters. Routers that rely on older routing protocols (i.e. RIP) are not capable of interpreting classless IP addresses. Internet Gateways Gateways are a combination of software and hardware that enable two different network segments to exchange data. A gateway facilitates communication between different networks or subnets. Because on device cannot send data directly to a device on another subnet, a gateway must intercede and hand off the information. Every device on a TCP/IP based network has a default gateway (a gateway that first interprets its outbound requests to other subnets, and then interprets its inbound requests from other subnets). The internet contains a vast number of routers and gateways. If each gateway had to track addressing information for every other gateway on the Internet, it would be overtaxed. Instead, each handles only a relatively small amount of addressing information, which it uses to forward data to another gateway that knows more about the data’s destination. The gateways that make up the internet backbone are called core gateways. Address Translation An organizations default gateway can also be used to “hide” the organizations internal IP addresses and keep them from being recognized on a public network. A public network is one that any user may access with little or no restrictions. On private networks, hiding IP addresses allows network managers more flexibility in assigning addresses. Clients behind a gateway may use any IP addressing scheme, regardless of whether it is recognized as legitimate by the Internet authorities but as soon as those devices need to go on the internet, they must have legitimate IP addresses to exchange data. When a clients transmission reaches the default gateway, the gateway opens the IP datagram and replaces the client’s private IP address with an Internet recognized IP address. This process is known as NAT (Network Address Translation). TCP/IP Mail Services All Internet mail services rely on the same principles of mail delivery, storage, and pickup, though they may use different types of software to accomplish these functions. Email servers and clients communicate through special TCP/IP application layer protocols. These protocols, all of which operate on a variety of operating systems are discussed below… SMTP (Simple Mail transfer Protocol) The protocol responsible for moving messages from one mail server to another over TCP/IP based networks. SMTP belongs to the application layer of the ODI model and relies on TCP as its transport protocol. Operates from port 25 on the SMTP server Simple sub-protocol, incapable of doing anything more than transporting mail or holding it in a queue MIME (Multipurpose Internet Mail Extensions) The standard message format specified by SMTP allows for lines that contain no more than 1000 ascii characters meaning if you relied solely on SMTP you would have very short messages and nothing like pictures included in an email. MIME us a standard for encoding and interpreting binary files, images, video, and non-ascii character sets within an email message. MIME identifies each element of a mail message according to content type. MIME does not replace SMTP but works in conjunction with it. Most modern email clients and servers support MIME POP (Post Office Protocol) POP is an application layer protocol used to retrieve messages from a mail server POP3 relies on TCP and operates over port 110 With POP3 mail is delivered and stored on a mail server until it is downloaded by a user Disadvantage of POP3 is that it typically does not allow users to save their messages on the server because of this IMAP is sometimes used IMAP (Internet Message Access Protocol) IMAP is a retrieval protocol that was developed as a more sophisticated alternative to POP3 The single biggest advantage IMAP4 has over POP3 is that users can store messages on the mail server, rather than having to continually download them Users can retrieve all or only a portion of any mail message Users can review their messages and delete them while the messages remain on the server Users can create sophisticated methods of organizing messages on the server Users can share a mailbox in a central location Disadvantages of IMAP are typically related to the fact that it requires more storage space on the server. Additional TCP/IP Utilities Nearly all TCP/IP utilities can be accessed from the command prompt on any type of server or client running TCP/IP. The syntaxt may differ depending on the OS of the client. Below is a list of additional TCP/IP utilities – research their use on your own! Ipconfig (Windows) & Ifconfig (Linux) Netstat Nbtstat Hostname, Host & Nslookup Dig (Linux) Whois (Linux) Traceroute (Tracert) Mtr (my traceroute) Route

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• The Alexandria Project, Chap. 12: Now You See Me (Now You Don't!)

  <b>Standards Blog:</b> "Frank was leaning back in his cubicle chair, feet up on his desktop. That way he could keep an eye on Carl Cumming&#8217;s office down the corridor. The guy must have the bladder of a camel, he thought. Wouldn&#8217;t he ever need to relieve himself?"

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• Organization &amp; Architecture UNISA Studies &ndash; Chap 4

  - by MarkPearl

  Learning Outcomes Explain the characteristics of memory systems Describe the memory hierarchy Discuss cache memory principles Discuss issues relevant to cache design Describe the cache organization of the Pentium Computer Memory Systems There are key characteristics of memory… Location – internal or external Capacity – expressed in terms of bytes Unit of Transfer – the number of bits read out of or written into memory at a time Access Method – sequential, direct, random or associative From a users perspective the two most important characteristics of memory are… Capacity Performance – access time, memory cycle time, transfer rate The trade off for memory happens along three axis… Faster access time, greater cost per bit Greater capacity, smaller cost per bit Greater capacity, slower access time This leads to people using a tiered approach in their use of memory   As one goes down the hierarchy, the following occurs… Decreasing cost per bit Increasing capacity Increasing access time Decreasing frequency of access of the memory by the processor The use of two levels of memory to reduce average access time works in principle, but only if conditions 1 to 4 apply. A variety of technologies exist that allow us to accomplish this. Thus it is possible to organize data across the hierarchy such that the percentage of accesses to each successively lower level is substantially less than that of the level above. A portion of main memory can be used as a buffer to hold data temporarily that is to be read out to disk. This is sometimes referred to as a disk cache and improves performance in two ways… Disk writes are clustered. Instead of many small transfers of data, we have a few large transfers of data. This improves disk performance and minimizes processor involvement. Some data designed for write-out may be referenced by a program before the next dump to disk. In that case the data is retrieved rapidly from the software cache rather than slowly from disk. Cache Memory Principles Cache memory is substantially faster than main memory. A caching system works as follows.. When a processor attempts to read a word of memory, a check is made to see if this in in cache memory… If it is, the data is supplied, If it is not in the cache, a block of main memory, consisting of a fixed number of words is loaded to the cache. Because of the phenomenon of locality of references, when a block of data is fetched into the cache, it is likely that there will be future references to that same memory location or to other words in the block. Elements of Cache Design While there are a large number of cache implementations, there are a few basic design elements that serve to classify and differentiate cache architectures… Cache Addresses Cache Size Mapping Function Replacement Algorithm Write Policy Line Size Number of Caches Cache Addresses Almost all non-embedded processors support virtual memory. Virtual memory in essence allows a program to address memory from a logical point of view without needing to worry about the amount of physical memory available. When virtual addresses are used the designer may choose to place the cache between the MMU (memory management unit) and the processor or between the MMU and main memory. The disadvantage of virtual memory is that most virtual memory systems supply each application with the same virtual memory address space (each application sees virtual memory starting at memory address 0), which means the cache memory must be completely flushed with each application context switch or extra bits must be added to each line of the cache to identify which virtual address space the address refers to. Cache Size We would like the size of the cache to be small enough so that the overall average cost per bit is close to that of main memory alone and large enough so that the overall average access time is close to that of the cache alone. Also, larger caches are slightly slower than smaller ones. Mapping Function Because there are fewer cache lines than main memory blocks, an algorithm is needed for mapping main memory blocks into cache lines. The choice of mapping function dictates how the cache is organized. Three techniques can be used… Direct – simplest technique, maps each block of main memory into only one possible cache line Associative – Each main memory block to be loaded into any line of the cache Set Associative – exhibits the strengths of both the direct and associative approaches while reducing their disadvantages For detailed explanations of each approach – read the text book (page 148 – 154) Replacement Algorithm For associative and set associating mapping a replacement algorithm is needed to determine which of the existing blocks in the cache must be replaced by a new block. There are four common approaches… LRU (Least recently used) FIFO (First in first out) LFU (Least frequently used) Random selection Write Policy When a block resident in the cache is to be replaced, there are two cases to consider If no writes to that block have happened in the cache – discard it If a write has occurred, a process needs to be initiated where the changes in the cache are propagated back to the main memory. There are several approaches to achieve this including… Write Through – all writes to the cache are done to the main memory as well at the point of the change Write Back – when a block is replaced, all dirty bits are written back to main memory The problem is complicated when we have multiple caches, there are techniques to accommodate for this but I have not summarized them. Line Size When a block of data is retrieved and placed in the cache, not only the desired word but also some number of adjacent words are retrieved. As the block size increases from very small to larger sizes, the hit ratio will at first increase because of the principle of locality, which states that the data in the vicinity of a referenced word are likely to be referenced in the near future. As the block size increases, more useful data are brought into cache. The hit ratio will begin to decrease as the block becomes even bigger and the probability of using the newly fetched information becomes less than the probability of using the newly fetched information that has to be replaced. Two specific effects come into play… Larger blocks reduce the number of blocks that fit into a cache. Because each block fetch overwrites older cache contents, a small number of blocks results in data being overwritten shortly after they are fetched. As a block becomes larger, each additional word is farther from the requested word and therefore less likely to be needed in the near future. The relationship between block size and hit ratio is complex, and no set approach is judged to be the best in all circumstances.   Pentium 4 and ARM cache organizations The processor core consists of four major components: Fetch/decode unit – fetches program instruction in order from the L2 cache, decodes these into a series of micro-operations, and stores the results in the L2 instruction cache Out-of-order execution logic – Schedules execution of the micro-operations subject to data dependencies and resource availability – thus micro-operations may be scheduled for execution in a different order than they were fetched from the instruction stream. As time permits, this unit schedules speculative execution of micro-operations that may be required in the future Execution units – These units execute micro-operations, fetching the required data from the L1 data cache and temporarily storing results in registers Memory subsystem – This unit includes the L2 and L3 caches and the system bus, which is used to access main memory when the L1 and L2 caches have a cache miss and to access the system I/O resources

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• Organization &amp; Architecture UNISA Studies &ndash; Chap 13

  - by MarkPearl

  Learning Outcomes Explain the advantages of using a large number of registers Discuss the way in which compilers optimize register usage Discuss the evolution of CISC machines Describe the characteristics of RISC architecture Discuss the RISC vs. CISC controversy Describe the way in which RISC and CISC design principles can be combined Instruction Execution Characteristics To understand the the line of reasoning of RISC advocates, we need a brief overview of instruction execution characteristics. These include… Operations Operands Procedure Calls These three sections can be studied in depth in the textbook at pages 503 - 505 A number of groups have come up with the conclusion that the attempt to make the instruction set architecture closer to HLLs (High Level Languages) is not the most effective design strategy. Rather HLL’s can be best supported by optimizing performance of the most time-consuming features of typical HLL programs. Generally 3 main characteristics came up to improve performance… Use a large number of registers or use a compiler to optimize register usage Careful attention needs to be paid to the design of instruction pipelines A simplified (reduced) instruction set is indicated The use of a large register optimization One of the most important design principles of RISC machines is the use of a large number of registers. The concept of register windows and the use of a large register file versus the use of cache memory are discussed. On the face of it, the use of a large set of registers should decrease the need to access memory. The design task is to organize the registers in such a fashion that this goal is realized. Read page 507 – 510 for a detailed explanation. Compiler-based register optimization   Reduced Instructions Set Architecture There are two advantages to smaller programs… Because the program takes up less memory, there is a savings in that resource (this was more compelling when memory was more expensive) Smaller programs should improve performance, and this will happen in two ways – fewer instructions means fewer instruction bytes to be fetched and in a paging environment smaller programs occupy fewer pages, reducing page faults. Certain characteristics are common to RISC processors… One instruction per cycle Register-to-register operations Simple addressing modes Simple instruction formats RISC vs. CISC After initial enthusiasm for RISC machines, there has been a growing realization that RISC designs may benefit from the inclusion of some CISC features CISC designs may benefit from the inclusion of some RISC features

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• Alexandria Project, Chap. 18: More than One Can Play that Game

  <b>Standards Blog:</b> "Crouching like a pack of hyenas on the floor between the subcommittee and witness tables were dozens of photographers, polishing their lenses in anticipation of the kill"

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• The Alexandria Project, Chap. 15: The Alexandria Project Makes the Evening News

  <b>Standards Blog:</b> "Good evening. We begin tonight with the shocking story of how the U.S. Government has hidden the threat of global collapse from the American People."

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• Problem connecting to isp server using xl2tpd as client. Ubuntu server 13.04

  - by Deon Pretorius

  I have followed guides found on google and ubuntu support pages and can get xl2tpd connection up but only under the following conditions: 1 - ADSL model must be configured and connected to the ISP or 2 - ADSL modem in bridge mode I must have an existing PPPoe connection established. If neither of the above are active xl2tpd wont trigger pppd and connect to the isp and thus tunnel connection fails to connect to the L2TP server of the ISP. Am I doing something wrong; /etc/ppp/options.l2tpd.axxess ipcp-accept-local ipcp-accept-remote refuse-eap refuse-chap require-pap noccp noauth idle 1800 mtu 1200 mru 1200 defaultroute usepeerdns debug lock connect-delay 5000 name (name used for ppp connection) /etc/ppp/pap-secrets # * password (name used for ppp connection as above) * (ppp password supplied by isp) /etc/xl2tpd/xl2tpd.conf [global] ; Global parameters: auth file = /etc/xl2tpd/l2tp-secrets ; * Where our challenge secrets are access control = yes ; * Refuse connections without IP match debug tunnel = yes [lac axxess] lns = 196.30.121.50 ; * Who is our LNS? redial = yes ; * Redial if disconnected? redial timeout = 5 ; * Wait n seconds between redials max redials = 5 ; * Give up after n consecutive failures hidden bit = yes ; * User hidden AVP's? length bit = yes ; * Use length bit in payload? require pap = yes ; * Require PAP auth. by peer require chap = no ; * Require CHAP auth. by peer refuse chap = yes ; * Refuse CHAP authentication require authentication = yes ; * Require peer to authenticate name = BLA85003@axxess ; * Report this as our hostname ppp debug = yes ; * Turn on PPP debugging pppoptfile = /etc/ppp/options.l2tpd.axxess ; * ppp options file for this lac /etc/xl2tpd/l2tp-secrets # Secrets for authenticating l2tp tunnels # us them secret # * marko blah2 # zeus marko blah # * * interop * vzb_l2tp (*** secret supplied by isp) ^ isp server host name Any help will be greatly appreciated

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• Routing tables don't show ppp0 after 12.04 kernel upgrade to 3.5.0: Haier CE682 modem configuration

  - by ubunsteve

  I'm trying to get my Haier CE682 EVDO modem, model number 201e:1022 to work in ubuntu 12.04 kernel 3.5.0-030500-generic #201207211835 . I had it working in a previous 12.04 kernel, using compat-wireless and these instructions http://zulkhamsyahmh.blogspot.com/2012/05/install-smartfren-haier-ce682-on-ubuntu.html, and to get it working had to edit the routing tables so that there was a ppp0 showing up, as suggested at http://www.linuxquestions.org/questions/slackware-14/wvdial-is-connecting-but-im-unable-to-do-anything-714861/ Network manager doesn't work with this modem, so I use either wvdial or gpppon to connect to it, both which work (after I run the command sudo modprobe usbserial vendor=0x201e product=0x1022 ) This is the output of when I connect with gpppon to the modem: Using interface ppp0 Connect: ppp0 <-- /dev/ttyUSB0 sent [LCP ConfReq id=0x1 ] rcvd [LCP ConfAck id=0x1 ] rcvd [LCP ConfReq id=0x2 ] sent [LCP ConfAck id=0x2 ] sent [LCP EchoReq id=0x0 magic=0x819c86db] rcvd [CHAP Challenge id=0x1 <1ac8f12799e953967a3cc222c9254690, name = ""] sent [CHAP Response id=0x1 <6f12a903dc40915ca2761c17b87f8fbd, name = "smart"] rcvd [LCP EchoRep id=0x0 magic=0x0] rcvd [CHAP Success id=0x1 ""] CHAP authentication succeeded CHAP authentication succeeded sent [CCP ConfReq id=0x1 ] sent [IPCP ConfReq id=0x1 ] rcvd [IPCP ConfReq id=0x1 ] sent [IPCP ConfAck id=0x1 ] rcvd [CCP ConfReq id=0x1] sent [CCP ConfAck id=0x1] rcvd [CCP ConfRej id=0x1 ] sent [CCP ConfReq id=0x2] rcvd [IPCP ConfRej id=0x1 ] sent [IPCP ConfReq id=0x2 ] rcvd [CCP ConfAck id=0x2] rcvd [IPCP ConfNak id=0x2 ] sent [IPCP ConfReq id=0x3 ] rcvd [IPCP ConfAck id=0x3 ] not replacing existing default route via 192.168.3.1 local IP address 10.191.248.154 remote IP address 10.17.95.25 primary DNS address 10.17.3.244 secondary DNS address 10.17.3.245 as you can see there is a problem with "not replacing existing default route via 192.168.3.1" This it the out put of route Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface default 192.168.3.1 0.0.0.0 UG 0 0 0 wlan0 link-local * 255.255.0.0 U 1000 0 0 wlan0 192.168.3.0 * 255.255.255.0 U 2 0 0 wlan0 I had tried these commands, which had previously worked in the earlier kernel: route del default route add default ppp0 but that broke my wireless internet connection. I then added the default routing as shown above with sudo route add default gw 192.168.3.1 wlan0 So it seems I need to add or change the routing to show a ppp0 connection, but I don't know how to do that.

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• The Alexandria Project, Chap. 9 &amp;#8211; You've Got Mail!

  <b>Standards Blog:</b> "Our story so far: Now under surveillance, Frank begins to plan his escape."

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• \ref Chapter Name in LaTeX

  - by joec

  Is it possible to use \ref{chap:conclusion} to refer to the actual name of the chapter instead of the chapter counter in LaTeX? So that I can do this: See the \ref{chap:conclusion} chapter for more information See the Conclusion chapter for more information instead of: See Chapter \ref{chap:conclusion} for more See Chapter 6 for more Thanks

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