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• Simulating a low-bandwidth, high-latency network connection on Linux

  - by Justin L.

  I'd like to simulate a high-latency, low-bandwidth network connection on my Linux machine. Limiting bandwidth has been discussed before, e.g. here, but I can't find any posts which address limiting both bandwidth and latency. I can get either high latency or low bandwidth using tc. But I haven't been able to combine these into a single connection. In particular, the example rate control script here doesn't work for me: # tc qdisc add dev lo root handle 1:0 netem delay 100ms # tc qdisc add dev lo parent 1:1 handle 10: tbf rate 256kbit buffer 1600 limit 3000 RTNETLINK answers: Operation not supported How can I create a low-bandwidth, high-latency connection, using tc or any other readily-available tool?

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• Ubuntu 12.04 suddenly cannot connect to WPA2/WPA Personal protected connection. Windows 7 can

  - by d4ryl3

  I have a laptop with Windows 7 and Ubuntu 12.04. I have a Cisco E1200 and when I set it up, it created 2 SSIDs. Let's name them: MyConnection (WPA/WPA2 personal), and MyConnection-Guest (no authentication, guest password entered via web browser). I had no problem connecting to MyConnection before, either in Windows 7 and Ubuntu. But now, I can't access MyConnection on Ubuntu. It just says "connecting..." then disconnects after a while. But I'm able to access the internet (on Ubuntu) when I connect to MyConnection-Guest. MAC filtering is off (even if it's on its MAC address is in the white list). Any idea why I'm unable to connect to MyConnection in Ubuntu? Thanks. Update: My Ubuntu installation can connect to ANY WiFi connection (WPA/WEP/no auth), except for MyConnection. Update2: This is what "The not so easy way" returned: Initializing interface 'eth1' conf '/etc/wpa_supplicant.conf' driver 'default' ctrl_interface 'N/A' bridge 'N/A' Configuration file '/etc/wpa_supplicant.conf' -> '/etc/wpa_supplicant.conf' Reading configuration file '/etc/wpa_supplicant.conf' Priority group 0 id=0 ssid='MyConnection' id=1 ssid='MyConnection' id=2 ssid='MyConnection' id=3 ssid='MyConnection' WEXT: cfg80211-based driver detected SIOCGIWRANGE: WE(compiled)=22 WE(source)=21 enc_capa=0xf capabilities: key_mgmt 0xf enc 0xf flags 0x0 netlink: Operstate: linkmode=1, operstate=5 Own MAC address: xx:xx:xx:xx:xx:xx wpa_driver_wext_set_key: alg=0 key_idx=0 set_tx=0 seq_len=0 key_len=0 wpa_driver_wext_set_key: alg=0 key_idx=1 set_tx=0 seq_len=0 key_len=0 wpa_driver_wext_set_key: alg=0 key_idx=2 set_tx=0 seq_len=0 key_len=0 wpa_driver_wext_set_key: alg=0 key_idx=3 set_tx=0 seq_len=0 key_len=0 wpa_driver_wext_set_key: alg=0 key_idx=4 set_tx=0 seq_len=0 key_len=0 ioctl[SIOCSIWENCODEEXT]: Invalid argument Driver did not support SIOCSIWENCODEEXT wpa_driver_wext_set_key: alg=0 key_idx=5 set_tx=0 seq_len=0 key_len=0 ioctl[SIOCSIWENCODEEXT]: Invalid argument Driver did not support SIOCSIWENCODEEXT wpa_driver_wext_set_countermeasures RSN: flushing PMKID list in the driver Setting scan request: 0 sec 100000 usec WPS: UUID based on MAC address - hexdump(len=16): 16 3b d8 47 9e 24 50 89 96 16 6d 66 35 f3 58 37 EAPOL: SUPP_PAE entering state DISCONNECTED EAPOL: Supplicant port status: Unauthorized EAPOL: KEY_RX entering state NO_KEY_RECEIVE EAPOL: SUPP_BE entering state INITIALIZE EAP: EAP entering state DISABLED EAPOL: Supplicant port status: Unauthorized EAPOL: Supplicant port status: Unauthorized Added interface eth1

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• Optimizing wireless router speed and minimizing interference.

  - by Tchalvak

  I've been experiencing problems with my wireless connectivity lately, and want to make sure that it's not related to the abundance of other wireless routers here in my building. So, what I'm looking for is a method (probably via some application or another) to audit the wireless channels (and other factors that might be important that I don't even know of yet) that are floating through the aether around me. Ubuntu or other linux apps are preferred, but some kind of windows/mac solution is possible, since I do have other OSes around me that I could install & test on. Router: netgear WGT624 v3 Hearsay tells me that channels 1, 6, and 11 are "non-overlapping" (I expect they aren't used for non-wireless-router purposes or something, not sure how they couldn't overlap with other routers using other channels), so perhaps my best choices of channel are limited, so if channels aren't really a big concern, I'd be happy to get links to other optimizations that I should look into.

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• Routing RFC1918 addresses through dd-wrt via a switch

  - by espenfjo

  I am a bit stuck with an experiment of mine. I have a network looking somewhat like this. | Internet | | ---- |Switch| ---- | | Server w/pub IP | DD-WRT router 192.168.1.1 | | RFC1918 clients 192.168.1.0/24 What I want is for the RFC1918 clients to speak directly with each others. On the server with the public IP I have this route: 192.168.1.0/24 dev eth0 scope link and can see that packets are infact reaching the dd-wrt router for 192.168.1.1, even though if I get no answer. Trying to reach one of the RFC1918 clients from the public IP server will get no result, as the dd-wrt router is not announcing that network on to its external interface (arp who-has 192.168.1.107 tell xxx.xxx.xxx.xxx, but no answer). The router being an WLAN dd-wrt router has of course a load of routes, VLANs and interfaces: xxx.xxx.xxx.1 dev vlan2 scope link 192.168.1.0/24 dev br0 proto kernel scope link src 192.168.1.1 192.168.1.0/24 dev eth1 proto kernel scope link src 192.168.1.244 84.215.64.0/18 dev vlan2 proto kernel scope link src xxx.xxx.xxx.xxx 169.254.0.0/16 dev br0 proto kernel scope link src 169.254.255.1 127.0.0.0/8 dev lo scope link 0.0.0.0 via xxx.xxx.xxx.1 dev vlan2 xxx.xxx.xxx.xxx being the public IP, and xxx.xxx.xxx.1 being the default route for the public IP. I am not sure where to continue with this. I would recon that I both need routing on the dd-wrt router, as well as some iptables magic? Why do something this complex? Why not ;) Also, do not mind that "Internet" can get RFC1918 traffic, it wont go outside of the walls. EDIT 1: Following the tip from stew I do indeed get the correct ARP flowing. And adding an iptables rule for allowing traffic from that specific public IPd machine I get traffic between the systems! Oddly enough though, the speed I get from Server w/pub IP - RFC1918 clients are the same as if the traffic were routed out onto the Internet and back. Edit 2: Ok, disconnecting the external Internet connection will still give the same, crappy transfer speed. So it has to be something else. Edit 3: Ok, I guess there are other reasons for this crappy speed. Case closed. :)

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• Is browser based wireless authentication secure?

  - by johnnyb10

  Our wireless network previously used a preshared WPA/WPA2 key for guest access, which allows them access to the Internet. (Our employee access uses 802.1x authentication). We just had a wireless consultant come in to fix various wireless issues we had; one of the things he wound up doing was changing our guest access to HTML-based instead of the preshared key. So now that guest SSID is open (instead of using WPA) and users are presented with a browser-based login screen before they can get on the Internet. My question is: Is this an acceptable method from a security standpoint? I would assume that having an open network is necessarily a bad idea, but the consultant said that the traffic is still using PEAP, so it's secure. I didn't get a chance to question him further on this because we ran late and a bunch of other things came up. Please let me know what you think about the advantages/disadvantages of using HTML-based wireless authentication as opposed to using a preshared WPA key. Thanks...

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• Can I connect an external antenna to a range extender?

  - by ercan

  I live in a kind of dormitory and the next access point is 60 meters away from my room. So I bought a range extender (TP-Link WA730RE) and installed it into my room in the same height as the access point. But my problem is still not solved. The reception is slightly better but my connection still gets broken every two minutes. The antenna that comes with this range extender was 4dB. My question is, can I buy an 8dB external antenna (like this one: http://www.amazon.com/TP-Link-TL-ANT2408C-Desktop-Omni-Directional-Antenna/dp/B0034CQSKW/ref=sr_1_14?ie=UTF8&qid=1332074993&sr=8-14) and replace it with the antenna that comes with the range extender? Or is this external antenna only suitable for the "receiver" end of the connection, i.e. the computer?

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• Windows redirect traffic to different DNS name not fixed IP address (hosts file equivalent)

  - by Arik Raffael Funke

  Using the Windows hosts file, one can redirect traffic for a domain to a specific IP address, e.g. domainA.com -- 127.0.0.1 I am looking for a SIMPLE way to do the same, but for a target domain name not for a target IP address (as this is dynamic), I.e. domainA.com -- domainB.com Addition: After the getting some initial answers I think I need to concretise my question. Situation: I have an application which looks up the IP of the target domain via DNS and then connects via HTTP to the IP address. I do not have control over any proxy settings. Option 1 Basically I am looking for a way to: intercept DNS requests for a domainA.com launch a DNS request for a domainB.com serve the IP of domainB.com in response to the request for domainA.com Without running an entire DNS server. Option 2 If a DNS server is the only way, in the alternative I would also be happy with an solution to how to define a non-standard DNS-server for a single application. Any ideas for wrapper applications, etc?

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• How do I know how many bandwidth an individual application are consuming on Mac OS X?

  - by overboming

  I mean for individual application, if it doesn't provide this kind of functionality.

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• datacenter network change control best practices

  - by jpolache

  I have been tasked with compiling a list of possible network equipment changes at a data center. The task includes tagging which changes need change control and which don't. Does anyone know of a "best practices" list that I can start from? The methods for doing change control at this data center are well established. The list would be of specific configuration items that should or should not be included in the change control process, of example; static route entries switch port assignments firewall rule additions/changes etc.

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• finding the best network latency between two countries

  - by Yoav Aner

  I know there are many tools to test for bandwidth and latency, but they all rely on having at least one host from which you can run those tests. I wonder whether there's an online source or some other way to guestimate the latency or speed between two countries (in general). For example, would a customer in Japan get lower latency if the server is located in Singapore or Australia? Is a user in India likely to get higher download speed from a server in the UK or in the US? Are there any online resources or some clever ways to answer those questions with a reasonable degree of accuracy? [UPDATE]: Thanks for the great suggestions from Raffael Luthiger. I didn't know about those looking glass servers. The submarine cable maps were also really cool to discover (Thanks to Jesper Mortensen). Also seems really wise if I could ask those network professional in the area for their experience, but obviously I don't have access to those. At least some of them are on SF :) However, I'm still a little unsure how to combine those resources to give me some measurements. This is the information I have: Two countries (A,B). I do have IP addresses of customers in country A (I can obtain those from the web server log files for example). Presumably I can find some looking glass servers in country B and run a trace to those IPs. What's the best measurements to use? Are there any scripts that help automate at least some of this process?

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• UAE and the mysteries of unreachable websites

  - by 0plus1

  I write here because I'm really lost, please stay with me because it's not easy to explain. A company asked me to set-up a private server, now I'm a programmer so I got a solution with technical support and cpanel which helped me to setup everything and it's working smoothless. I'm by no means a professional sysadmin, but I have a fair knowledge of server configurations, but this problem is way over my knowledge, and apparently way over the knowledge of most sysadmins, I really hope that here I'll find someone with enough experience to help me or at least give me more insight. Now this company for which I'm consulting operates in the UAE (United Arab Emirates) and from there the server is almost unreachable. It started with ns not registering in the UAE, after a week that sorted itself out and now the site is indeed reachable, but it takes almost 2 minutes to load a webpage with one line of text. Emails go in timeout. The domain currently parked there has been bought appositely for tests, the main one that was supposed to go there, after a catastrophic week has been transferred to a shared hosting solution in the UK, and from there it works like a charme. Now after doing some research I discovered that I'm not alone in this, there are several reports of webmasters discovering that their website is not reachable inside the UAE, and mind this has nothing to do with the state-wide block of questionable sites, because in that case an error message appears, this seems to be related to the infrastructure of the UAE, which apparently reroutes everything through their own "fake" internet. Apparently new servers with their own IP are not recognized (yet?) by the UAE infrastructure, while shared hosting solutions seeing that they operates tons of other websites are more likely to be part of the UAE network. Now my questions are: 1) Has someone a real explanation for this? The only thing I can think of is that the server is on a new IP that is not yet recognized by the UAE, but that doesn't explain why it loads (even if after 2 minutes). I don't have any help from within the UAE as the only people that are "experts" are questionable companies that simply try to sell their own services. 2) If there is really some kind of block of new servers, is it possible to know before if a server is reachable from within the UAE, currently this is not a ns problem as even accessing the server with its IP result in a 2 minute wait. 3) Can it be that the problem lies somewhere else? There are some tests that I can perform? I'm not physically in the UAE, but I can ask the people there, or use teamviewer. Could it be some misconfiguration on the server (mind that the site works EVERYWHERE else in the world). Thank you for ANY kind of help

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• OS X will not register newly installed network adapters

  - by Chris

  I have purchased an Edimax 7318USg and tested it on a Windows machine (works). The installation process for the software for this adapter runs smoothly. However, OS X simply does not recognize new network adapters. When you go to System Preferences/Network, a new network adapter should be present/there should be an alert. This is not the case. Why might this be? Is there a setting I may reset to force the operating system to recognize this? Thanks!

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• Does an unmanaged 4/8-port GBit Ethernet switch with a GBIC port exist?

  - by Aaron Digulla

  I'm looking for a simple unmanaged switch with 4-8 GBit Ethernet ports and a fiber port (either as a GBIC slot or pre-installed with a 1000BASE-SX port). Does something like that exist? [EDIT] I want to connect to places in my home without drilling large holes though the floors. Therefore, I'm looking for a cheap way to connect two GBit switches via fiber. I tried with a media converter (GBit <- multimode fiber) but that costs about 50% throughput. So I was hoping that there is a cheap, small GBit switch which has a GBIC slot). All I found so far are very expensive managed switches with 12 or 24 ports for industry use.

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• Vista laptop 1 connects to network but Vista laptop 2 doesn't

  - by Jaips

  (Sorry if this is a dulipcate. I did a hunt but couldn't find matching question) We recently got a new router for our network (thomson TG585v8). It was already pre-configured by the ISP and was easy to setup. Both Vista laptops in this home network connected without trouble as well a iPod touch, all via wifi. In the last two days one of the laptops has been unable to connect cleanly to the network (connects as unidentified network). The other laptop, and iPod have not had any issues. I can't think of anything that has changed to make this happen now. I have rebooted the laptop and the router. I have updated the laptop wireless driver I have checked the laptop is set to automatically get IP I have logged into the router which correctly identifies all three wireless devices. The problem laptop connects via LAN without issue. Some things that may or may not matter: The problem laptop also sometimes uses a 3G dongle Both laptops use Windows Live Mesh to sync folders Laptop is usually set to go to sleep NB: it seems this is an intermittent issue, after an hour (since i noticed it) it seems to have fixed itself. Would love ideas though to solve this problem for good.

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• Monitoring bandwidth/latency/jitter between 2 sites?

  - by TheCleaner

  I have 2 sites connected via an MPLS network and I'd like to do the following: setup a host on each end that can "talk" back and forth between each other and somehow report/log what kind of throughput, jitter, latency, etc. they are experiencing between each other in 5 minute intervals. Something similar to Qcheck but that can be automated. Bottom line is I'm trying to determine if the WAN network is "stable" throughout the day or if something is wrong. We have video conferences between these sites and even at 1024kbps calls we are experiencing delays and jitter. I'm hoping to exonerate the network with some testing.

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• Blocking ICMP outgoing requests only in eth1

  - by Raj

  I am creating a NAT with iptables: Computer A: eth0 (dhcp) + eth1 (static ip 192.168.0.1 - gateway) Computer B: eth1 (static ip 192.168.0.2, using Computer A as gateway) I know how to block ICMP outgoing requests (-A OUTPUT -p icmp --icmp-type echo-request -j DROP), but that would block ICMP requests from Computer A, but not from Computer B (in fact, only for Computer A - Computer B can keep doing those). I tried with the same command, but adding -o eth1, but that does not block at all. Any idea?

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• What's the correct term for this network connection?

  - by Preet Sangha

  What is the correct general term for the network connection on mobile devices that can connect to networks via telecoms links? Question asked "my device is not connecting to my local web server here". My response "Are you using Wifi or XXXX to to connect?" Where XXXX is the network connection through the phone system - e.g. 3g, gprs, etc... What is the general term encompassing term for XXXX please?

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• What to use for small scale server and network documentation? Must run on Linux.

  - by Louise Hoffman

  Does anyone know of a good program, web service, or CMS for documenting servers, IP addresses, logins, and network? Only requirement it must run on and from Linux. And it is just for a small network of 10-15 servers.

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• How to set up a wireless AP with a linux box and SOCKS proxy

  - by user50455

  I've got: (1) Linux box (Arch linux to be precise, but that doesn't really matter) (2) Ethernet connection on it (say, eth0) (3) Socks proxy on a remote site (say, remote :port), which can be accessed through (2) (4) Wireless card on local linux box (say, eth1) So, the task is: create a wireless access point using (4) on local site (1) in such a way that all connections from it will go through proxy (3). E.g., when one simply connects to that AP (well, there should be DHCP or something for that) and goes to serverfault.com, all the traffic goes through that SOCKS proxy. I'm just asking for the digging direction and some references, not step-by-step tutorial. Thanks in advance

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• msi netbook refuses to connect to home wireless network (windows xp)

  - by sa125

  Hi - I'm trying to connect my girlfriend's MSI netbook to the wireless network in my house, and failing repeatedly. It's not a hardware issue, b/c it connects to other networks successfully, and, it's not a network issue, because I have another mac and linux laptops that have no problem detecting and connecting to the same network. When I open windows' network connections box, I can see the network available, and when I try to connect to it (using a password), I get a "network no longer in range.." error (the router is 2 ft away). This has been the case for the past 6 months, and I'm about to give up. I've reset the router, erased all saved network preferences and pretty much all I could think of short of re-installing XP. Any idea what else could be done? thanks.

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• How to ignore a set of Mac addresses in dhcpd.conf?

  - by Roberto Aloi

  Is it possible in dhcpd.conf to ignore requests from a set of MAC addresses? Something like this: host vminstances { hardware ethernet d0:0d:*; ignore booting; }

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• Homegroup doesn't show other computers, but "Network" does

  - by McPherrinM

  I have a desktop and a laptop (both running windows 7) in my Windows 7 homegroup. The desktop created the homegroup, and the laptop joined it. Both share a few folders. On the laptop, I have no problem accessing the Desktop's shared folders via the "Homegroup" sidebar button in Windows Explorer. However, on the Desktop, I get the message No other homegroup computers are currently available in the homegroup screen. However, if I go to the Network page, I can see the other computer and browse its shared media. These shares were made by right clicking and choosing "Share with Homegroup". I can access the media, so this isn't a big problem, but I'm just confused as to why the Homegroup screen denies the existence of the other computer. Has anybody else encountered and resolved this?

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• Managing an application across multiple servers, or PXE vs cfEngine/Chef/Puppet

  - by matt

  We have an application that is running on a few (5 or so and will grow) boxes. The hardware is identical in all the machines, and ideally the software would be as well. I have been managing them by hand up until now, and don't want to anymore (static ip addresses, disabling all necessary services, installing required packages...) . Can anyone balance the pros and cons of the following options, or suggest something more intelligent? 1: Individually install centos on all the boxes and manage the configs with chef/cfengine/puppet. This would be good, as I have wanted an excuse to learn to use one of applications, but I don't know if this is actually the best solution. 2: Make one box perfect and image it. Serve the image over PXE and whenever I want to make modifications, I can just reboot the boxes from a new image. How do cluster guys normally handle things like having mac addresses in the /etc/sysconfig/network-scripts/ifcfg* files? We use infiniband as well, and it also refuses to start if the hwaddr is wrong. Can these be correctly generated at boot? I'm leaning towards the PXE solution, but I think monitoring with munin or nagios will be a little more complicated with this. Anyone have experience with this type of problem? All the servers have SSDs in them and are fast and powerful. Thanks, matt.

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• nagios wrongly reports packet loss

  - by Alien Life Form

  Lately, on my nagios 3.2.3 install (CentOS5, monitoring ~ 300 hosts, 1150 services) has sdtarted to occasionally report high packet loss on 50-60 hosts at a time. Problem is it's bogus. Manual runs of ping (or its own check_ping binary) finds no fault with any of the affected hosts. The only possible cures I found so far are: run all the checks manually (they will succeed but it may act up again on next check) acknowledge and wait for the problem to go away (may take several ours) I suspect (but have no particular reason other than single rescheduled checks succeeding) that the problem may lay with all the checks being mass scheduled together - in which case introducing some jitter in the scheduling (how?) might help. Or it may be something completely different. Ideas, anyone?

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• Disabling networkmanager for a specific interface

  - by bdonlan

  I'd like to do some experimentation with hostap without disabling my primary wireless interface. How do I tell networkmanager to keep its hands off a specific interface or interfaces while allowing it to continue managing all other interfaces normally? I'm using Ubuntu 9.04. (Wasn't sure if this should go on superuser or serverfault, as networkmanager isn't much of a 'server' tool - if it belongs on serverfault please feel free to move it) Edit: I've tried adding this to /etc/network/interfaces: allow-hotplug wlan2 iface wlan2 inet static address 192.168.49.1 netmask 255.255.255.0 But this has no apparent effect, even after restarting NetworkManager. Here's my /etc/NetworkManager/nm-system-settings.conf: [main] plugins=ifupdown,keyfile [ifupdown] managed=false Edit[2]: Looks like I needed to restart nm-system-settings, then NetworkManager.

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