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• How to fix massive lag on ZyXEL HomePlug AV powerline adapters?

  - by Tim Abell

  I have 3 ZyXEL Homeplug AV powerline adapters as per the one in the review below. I have two plugged in currently, one into my Be / Thompson wireless router, and one into my desktop pc (box1). every now and then the link indicator on the adapters (the mains link, not the ethernet link) goes nutty, and performance falls off a cliff (see below). http://www.gadgetspeak.com/gadget/article.rhtm/753/479266/ZyXEL_PowerLine_HomePlug_AV_PLA401.html 64 bytes from box1 (192.168.1.101): icmp_seq=1064 ttl=64 time=996 ms 64 bytes from box1 (192.168.1.101): icmp_seq=1065 ttl=64 time=549 ms 64 bytes from box1 (192.168.1.101): icmp_seq=1066 ttl=64 time=6.15 ms 64 bytes from box1 (192.168.1.101): icmp_seq=1067 ttl=64 time=1400 ms 64 bytes from box1 (192.168.1.101): icmp_seq=1068 ttl=64 time=812 ms 64 bytes from box1 (192.168.1.101): icmp_seq=1069 ttl=64 time=11.1 ms 64 bytes from box1 (192.168.1.101): icmp_seq=1070 ttl=64 time=1185 ms 64 bytes from box1 (192.168.1.101): icmp_seq=1071 ttl=64 time=501 ms 64 bytes from box1 (192.168.1.101): icmp_seq=1072 ttl=64 time=1975 ms 64 bytes from box1 (192.168.1.101): icmp_seq=1073 ttl=64 time=970 ms ^C --- box1 ping statistics --- 1074 packets transmitted, 394 received, +487 errors, 63% packet loss, time 1082497ms rtt min/avg/max/mdev = 5.945/598.452/3526.454/639.768 ms, pipe 4 Any idea how to diagnose/fix? I'm on linux so installing the windoze software that came with them is not something I'm terribly keen to do.

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• Unable to Access Certain Websites

  - by codejoust

  Through a local network, all computers except one ubuntu machine can access 1. Adobe.com 2. Icann.org 3. Apache.org 4. Example.com. The ubuntu machine returns (in firefox): "Though the site seems valid, the browser was unable to establish a connection." Furthermore, when I traceroute those websites using the ubuntu machine, they all return ubuntu.local, and it ends there: (traceroute to icann.org (192.0.32.7), 30 hops max, 40 byte packets 1 ubuntu.local (192.168.1.105) 3000.791 ms !H 3000.808 ms !H 3000.814 ms !H I've checked the hosts file, and there isn't anything in there, and I have an apache server there so if it was redirected to localhost, I'd probably see the localhost webroot page. Thanks in advance! user@ubuntu:~$ netstat -nr Kernel IP routing table Destination Gateway Genmask Flags MSS Window irtt Iface 169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth1 192.0.0.0 0.0.0.0 255.0.0.0 U 0 0 0 eth1 0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 eth1 The Ubuntu Machine is one of six on the network. I'm using opendns for dns, so I do think that should be a problem.

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• Uninstall php5 installed from source

  - by diegomichel

  I have tried to install php5 from source , and it worked... Then for some reason need to install the official packets, so i tried a make uninstall and for my surprise there is such make uninstall... so i tried delete all the installed files by hand. Then installed the official debian packages and it worked fine... till i need install sqlite module, which give me the following error: php --version PHP Warning: PHP Startup: Unable to load dynamic library '/usr/lib/php5/20090626/pdo_sqlite.so' - /usr/lib/php5/20090626/pdo_sqlite.so: undefined symbol: php_pdo_register_driver in Unknown on line 0 PHP Warning: PHP Startup: Unable to load dynamic library '/usr/lib/php5/20090626/sqlite.so' - /usr/lib/php5/20090626/sqlite.so: undefined symbol: php_pdo_register_driver in Unknown on line 0 PHP 5.3.1-5 with Suhosin-Patch (cli) (built: Feb 22 2010 22:46:05) Copyright (c) 1997-2009 The PHP Group Zend Engine v2.3.0, Copyright (c) 1998-2009 Zend Technologies So i remember that manual install i did, and i think there is some old lib installed causing that problem, the bad thing is that there is not such make uninstall on the source code of php5... php-5.2.13 > make uninstall make: *** No rule to make target `uninstall'. Stop. I have tried reinstall and purge all php related packages via aptitude with not success. OS: Debian Squeeze. uname -a Linux desktop 2.6.32-trunk-amd64 #1 SMP Sun Jan 10 22:40:40 UTC 2010 x86_64 GNU/Linux Any idea how to fix that?

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• Balancing internal services using a Cisco CSS 11501

  - by Ladadadada

  First, the background to the problem: I have a Cisco CSS11501 that I am using to load balance a few web servers. These web servers have two network interfaces, one internal and one external and we are sending the requests to the internal interface. We have the CSS configured to do NAT because our webservers need to see the client's IP address. Because the TCP packets hit the webservers with a source address on the Internet, the webserver tries to send the packet back to the client over the external interface and not through the load balancer. In order to stop these requests being sent back out to the Internet via the external interface, we added a routing rule on these boxes so that all traffic with a source address on the internet will use the load balancer as the gateway. This part works fine. What I would also like to to is use the CSS as a load balancer for internal services such as our MySQL slaves. When I do this, I run into a similar problem; the TCP connection goes from the web server to the load balancer and then from the load balancer to the MySQL slave but the CSS spoofs a source address of the original webserver. The MySQL slave then tries to send the response directly to the webserver via the internal network and not via the load balancer. The ideal solution would be to tell the CSS not to do source address spoofing on the internal network and only do it for requests originating on the Internet. Is this possible ? Failing that, is there a way of directing the load balanced traffic back through the load balancer while keeping the other traffic (say SSH) purely on the internal network ? Is there another way of using the CSS11501 to load balance internal services ?

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• Change OpenVZ route to pass through ip failover

  - by Kevin Campion

  I have one dedicaced server with its own IP and another IP (failover) who refer to the first. I will wish to change the gateway of a Proxmox virtual machine (openvz) who runs on this dedicaced server to go through the failover IP rather than the ip of host main server. Once connected to a virtual machine, when I do a traceroute VE# traceroute www.google.fr traceroute to www.google.fr (209.85.229.104), 30 hops max, 60 byte packets 1 MY_SERVER_NAME.ovh.net (xxx.xxx.xxx.xxx FIRST_IP_MAIN_SERVER) 0.021 ms 0.010 ms 0.009 ms The first line tells me the ip of host main server. I would like that the traceroute display the second IP failover. VE# route Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 192.0.2.1 * 255.255.255.255 UH 0 0 0 venet0 default 192.0.2.1 0.0.0.0 UG 0 0 0 venet0 With iptables HOST# iptables -t nat -L Chain POSTROUTING (policy ACCEPT) target prot opt source destination MASQUERADE all -- anywhere anywhere MASQUERADE all -- anywhere anywhere SNAT tcp -- anywhere 10.10.101.2 tcp dpt:www state NEW,RELATED,ESTABLISHED,UNTRACKED to:SECOND_IP_FAILOVER SNAT all -- 10.10.101.2 anywhere to:SECOND_IP_FAILOVER 10.10.101.2 is the virtual machine IP (interface venet0) Any ideas ?

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• postfix and iRedMail- Relaying Denied

  - by Lock

  I am trying to setup iRedMail and am way over my head here. I have installed it, and can send emails internally, but not externally. When I send an email from outside, I get the following return email: The error that the other server returned was: 550 550 5.7.1 <[email protected]>... Relaying denied (state 13). Now I have no idea where to start looking! Any ideas? I have really only just installed iRedMail so I am unsure what else I need to do to get it working. I've pointed my MX records to that server, so that shouldnt be the problem. Also- if i stop postfix (so nothing is listening on port 25) and send a test email, I get the same reply back. Why would I get the same reply back even if postfix is stopped? I have run tcpdump over 25 and can see the packets coming in/out, so its definitely a configuration issue! I suppose my question is not really "what is my problem", but more "What configuration needs to be completed on postfix and iRedMail?"

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• Assistance on setup to Connect an offsite server to the LAN via RRAS VPN - Server 2008 R2

  - by Paul D'Ambra

  I have an office LAN protected using a Zyxel Zywall USG 300. I've set up an L2TP/ipsec VPN on that which accepts connections using a shared secret and I've tested this from multiple clients. I have a server offsite and want to set up RRAS to use a persistent connection to the VPN so that it can carry out network jobs even with no one logged in (I'm using it for Micorosft DPM secondary backup). If I create a vpn as if I were setting up a users laptop it can dial in no problem but if I set up a demand dial interface in RRAS it errors. I enable RRAS ticking only demand dial interface (branch office routing) Select network interfaces, right click and choose new demand dial interface Name the VPN ToCompany Select connect using VPN And then L2TP as the vpn type enter the IP address (double-checked for typos!) select Route IP packets on this interface specify static route to remote network as 10.0.0.0/24 with metric of 1 add dial out credentials (again double checked for typos and confirmed with other vpn connections click finish now I right-click on the new interface and choose properties and then the security tab I change Data encryption to optional select only PAP for Authentication (both as per manufacturer of Zywall) click advanced settings against type of vpn and set shared secret then I select the new interface, right-click and choose connect this dials and then errors with either 720 or 811 as the error codes. However, if I create a VPN by going to Network & Sharing center and setting up as if I was creating a VPN from my laptop to the office (say) it dials successfully so I know the VPN settings are correct and the machine can connect to the VPN. Suggests very strongly the problem is how I'm setting up RRAS. Can anyone help?

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• Wireless to Wireless Transfer Slow on a Linksys WRT54GL

  - by Kyle Brandt

  The Situation: When I try to transfer a file from one computer to another that are both connected via wireless on a WRT54GL (in a office) with dd-wrt firmware I often get bad speeds. In generally they average around 100 kilobytes a second. Either computer can download via wireless from the Internet at at about 2 megabytes a second. The speed is slow with the transfer of one large file. There are about 20 other wireless networks that the computers can see, so there is a lot of noise, but I don't have the equipment to really monitor the frequencies well. But that still seems pretty slow. I thought maybe it was the transmit on each card, but even when they are 5 feet away with a line of sight I still get these speeds. According to Linux both cards are operating at 54g. My Questions: Is this normal for this sort of consumer level wireless equipment? Anything I can do to improve it? why is wireless to wireless transfer slow when everything else isn't? Whats steps might I take to figure out what is happening? For example, are lots of packets not making to the access point requiring retransmissions? Above all, I want to find out what the problem actually is. This may seem odd, but at this point I am more interested in understanding what the problem is than fixing it. What I have tried: I have tried messing with lots of settings. Different channels, xmit power, G-Only, none of which has made anything any better. I've also tried upgrading to newer dd-wrt firmware version and doing a reset to wipe out the settings.

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• Ubuntu Server attack? how to solve?

  - by saky

  Hello, Something (Someone) is sending out UDP packets sent from our whole ip range. This seems to be multicast DNS. Our server host provided this (Our IP Address is masked with XX): Jun 3 11:02:13 webserver kernel: Firewall: *UDP_IN Blocked* IN=eth0 OUT= MAC=01:00:5e:00:00:fb:00:30:48:94:46:c4:08:00 SRC=193.23X.21X.XX DST=224.0.0.251 LEN=73 TOS=0x00 PREC=0x00 TTL=255 ID=0 DF PROTO=UDP SPT=5353 DPT=5353 LEN=53 Jun 3 11:02:23 webserver kernel: Firewall: *UDP_IN Blocked* IN=eth0 OUT= MAC=01:00:5e:00:00:fb:00:30:48:94:46:c4:08:00 SRC=193.23X.21X.XX DST=224.0.0.251 LEN=73 TOS=0x00 PREC=0x00 TTL=255 ID=0 DF PROTO=UDP SPT=5353 DPT=5353 LEN=53 Jun 3 11:02:32 webserver kernel: Firewall: *UDP_IN Blocked* IN=eth0 OUT= MAC=01:00:5e:00:00:fb:00:30:48:94:46:c4:08:00 SRC=193.23X.21X.XX DST=224.0.0.251 LEN=73 TOS=0x00 PREC=0x00 TTL=255 ID=0 DF PROTO=UDP SPT=5353 DPT=5353 LEN=53 Jun 3 11:02:35 webserver kernel: Firewall: *UDP_IN Blocked* IN=eth0 OUT= MAC=01:00:5e:00:00:fb:00:30:48:94:46:c4:08:00 SRC=193.23X.21X.XX DST=224.0.0.251 LEN=73 TOS=0x00 PREC=0x00 TTL=255 ID=0 DF PROTO=UDP SPT=5353 DPT=5353 LEN=53 I checked my /var/log/auth.log file and found out that someone from China (Using ip-locator) was trying to get in to the server using ssh. ... Jun 3 11:32:00 server2 sshd[28511]: Failed password for root from 202.100.108.25 port 39047 ssh2 Jun 3 11:32:08 server2 sshd[28514]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=202.100.108.25 user=root Jun 3 11:32:09 server2 sshd[28514]: Failed password for root from 202.100.108.25 port 39756 ssh2 Jun 3 11:32:16 server2 sshd[28516]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=202.100.108.25 user=root ... I have blocked that IP address using this command: sudo iptables -A INPUT -s 202.100.108.25 -j DROP However, I have no clue about the UDP multicasting, what is doing this? who is doing it? and how I can stop it? Anyone know?

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• Real benefits of tcp TIME-WAIT and implications in production environment

  - by user64204

  SOME THEORY I've been doing some reading on tcp TIME-WAIT (here and there) and what I read is that it's a value set to 2 x MSL (maximum segment life) which keeps a connection in the "connection table" for a while to guarantee that, "before your allowed to create a connection with the same tuple, all the packets belonging to previous incarnations of that tuple will be dead". Since segments received (apart from SYN under specific circumstances) while a connection is either in TIME-WAIT or no longer existing would be discarded, why not close the connection right away? Q1: Is it because there is less processing involved in dealing with segments from old connections and less processing to create a new connection on the same tuple when in TIME-WAIT (i.e. are there performance benefits)? If the above explanation doesn't stand, the only reason I see the TIME-WAIT being useful would be if a client sends a SYN for a connection before it sends remaining segments for an old connection on the same tuple in which case the receiver would re-open the connection but then get bad segments and and would have to terminate it. Q2: Is this analysis correct? Q3: Are there other benefits to using TIME-WAIT? SOME PRACTICE I've been looking at the munin graphs on a production server that I administrate. Here is one: As you can see there are more connections in TIME-WAIT than ESTABLISHED, around twice as many most of the time, on some occasions four times as many. Q4: Does this have an impact on performance? Q5: If so, is it wise/recommended to reduce the TIME-WAIT value (and what to)? Q6: Is this ratio of TIME-WAIT / ESTABLISHED connections normal? Could this be related to malicious connection attempts?

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• Is timeout in tracertoutput an indication of an error?

  - by nitramk

  TCP/IP packages sent from my computer to a remote server does not always reach destination and ends up being retransmitted sometimes several times before they succeed. To troubleshoot this, I'm running a tracert to the server: Tracing route to <site> [<address>] Over a maximum of 30 hops: 1 <1 ms <1 ms <1 ms mymachine 2 <1 ms <1 ms <1 ms gw.levonline.com [217.70.32.30] 3 <1 ms <1 ms <1 ms 81.201.213.218 4 <1 ms <1 ms <1 ms bmf1-hmf1.driften.net [81.201.213.12] 5 <1 ms <1 ms <1 ms 10ge-2-4-cr2.a1.sth.ownit.se [84.246.88.157] 6 <1 ms * <1 ms netnod-ix-ge-b-sth-4470.microsoft.com [195.69.11.181] 7 26 ms * * ge-3-0-0-0.ams-64cb-1a.ntwk.msn.net [207.46.42.1] 8 48 ms 57 ms 56 ms ten9-1.lts-76e-1.ntwk.msn.net [207.46.42.133] 9 * * * Request timed out. In step 6 and 7, I'm seeing timeouts while waiting for the reply from the server (as seen above). Running the same tracert many times gives varying output, sometimes the response is fine, but sometimes I get this timeout 1, 2 and sometimes for all 3 packets. The timeout always starts at the same server, netnod-ix-ge-b-sth-4470.microsoft.com. I've tried setting the tracert timeout to 10 seconds, but am still getting the timeout. Running tracert towards other servers does not give me the same timeout. Microsoft network technicians tells me that the problem is not on "their" side. Are these timeouts an indicator of a lost packet on the specific node which did not respond? Are the timeouts an indication of there being a problem, or is it normal?

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• NAT vs public IP (and blocked ports)

  - by user1646166

  I have a problem with my ISP. They say that they don't block any ports and I have public IP, while I think these both statements are false. Before I talk to them again (which is really tough when my understanding of these terms is different than theirs) I would like to make some things clear. It seems like my computer is behind NAT (is it possible to have public IP and be behind NAT at the same moment?). When I check my IP, through some external server, and type that IP into browser I get a home page of some router (not mine). Isn't that a proof that my IP isn't public? Also, I have problems with making connections via some ports. E.g. when I'm trying to connect through some high port ( 1023) via SSH, it doesn't work. Is it possible that certain range of outgoing ports from my computer are blocked? Or is it simply because that my ssh client (PuTTY) can't receive incoming packets because of blocked incoming ports? To avoid some questions: it's not a problem with my router, I tried connecting my PC directly and it also didn't work, while having connected by 3G using phone with USB tethering, it does work. Thanks!

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• Port forwarding + shared connection with Ubuntu

  - by Joey Adams

  Because my wireless router's ethernet ports are defective, I set up a shared wireless connection from my laptop (which has wifi) to my eMac (which does not) via a crossover ethernet cable. The laptop is behind a router as 192.168.1.131, and the eMac is behind the laptop as 10.42.43.1 . The laptop is running Ubuntu 9.10 (Karmic). I achieved the shared connection through NetworkManager Applet. I right-clicked on the network icon at the topright, went to Edit Connections, selected the Wired connection named "Auto eth0", clicked "Edit...", went to the "IPv4 Settings" tab, and selected the Method "Shared to other computers". The eMac can now access the Internet. Now I want to enable port forwarding. There's a game I want to play that needs port 6112 forwarded (both TCP and UDP) in order to host games. I set up the router to enable port forwarding for 192.168.1.131 (the laptop), but port forwarding still isn't available on the eMac. I suppose I need to pretend my laptop is a router and configure port forwarding on it, indicating that incoming connections to the laptop (192.168.1.131) should be forwarded to the eMac on the shared connection (10.42.43.1 ). Thus, packets coming into the router on port 6112 would be redirected to the laptop (by the router), then to the eMac (by the laptop). My question is, how would I do that on Ubuntu (in light of NetworkManager's presence)? Also, if I can't get this to work, does anyone mind hosting a comp stomp? :D

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• Possible to IPSec VPN Tunnel Public IP Addresses?

  - by caleban

  A customer uses an IBM SAS product over the internet. Traffic flows from the IBM hosting data center to the customer network through Juniper VPN appliances. IBM says they're not tunneling private IP addresses. IBM says they're tunneling public IP addresses. Is this possible? What does this look like in the VPN configuration and in the packets? I'd like to know what the source/destination ip/ports would look like in the encrypted tunneled IPSec Payload and in the IP packet carrying the IPSec Payload. IPSec Payload: source:1.1.1.101:1001 destination:2.2.2.101:2001 IP Packet: source:1.1.1.1:101 destination:2.2.2.1:201 Is it possible to send public IP addresses through an IPSec VPN tunnel? Is it possible for IBM to send a print job from a server on their network using the static-nat public address over a VPN to a printer at a customer network using the printer's static-nat public address? Or can a VPN not do this? Can a VPN only work with interesting traffic from and to private IP addresses?

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• Network latency and speed of light

  - by James

  This was kinda of covered by the following Is minimum latency fixed by the speed of light? , but i would like to add the follow up a bit. The scenario is as follows; we have two opposing sites one on the West Coast of the US and one in Ireland. The customer is in central Europe, and has requested a latency test. Ireland gives responses of ~65-70ms. However the West Coast guys claim to be faster with a response of 60ms. Now a quick check says that light in fiber would take about 42ms to make the trip to the States and 8.5ms to Ireland. So obviously this is a single hop and does not include routers, switches, firewalls, protocol overhead etc. Would I be right to call BS on their figures? As a final note I tested a ping to Google IP address that was allegedly on the west coast from a site that covered a similar distance and was amazed to get a response time of 20ms. Suggesting ICMP packets that travel twice the speed of light. So A) what am I missing B) Am I right to suspect shenanigans? UPDATE: Guys thanks so far for your help and I have been reading various previous questions on this. About 5 years I had an issue where the hop from the UK to Ireland added 10ms of latency no matter what we did. In the end I moved the servers; So imagine my surprise when I have guys that claim they are 5ms faster with a transatlantic trip. So again should I call BS? Oh and assume both sites are normal mortals that don't have access to Google magical routing, warp dives or flux capacitors. :)

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• Same netmask or /32 for secondary IP on Linux

  - by derobert

  There appear to be (at least) two ways to add a secondary IP address to an interface on Linux. By secondary, I mean that it'll accept traffic to the IP address, and responses to connections made to that IP will use it as a source, but any traffic the box originates (e.g., an outgoing TCP connection) will not use the secondary address. Both ways start with adding the primary address, e.g., ip addr add 172.16.8.10/24 dev lan. Then I can add the secondary address with either a netmask of /24 (matching the primary) or /32. If I add it with a /24, it gets flagged secondary, so will not be used as the source of outgoing packets, but that leaves a risk of the two addresses being added in the wrong order by mistake. If I add it with /32, wrong order can't happen, but it doesn't get flagged as secondary, and I'm not sure what the bad effects of that may be. So, I'm wondering, which approach is least likely to break? (If it matters, the main service on this machine is MySQL, but it also runs NFSv3. I'm adding a second machine as a warm standby, and hope to switch between them by changing which owns the secondary IP.)

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• CentOS 6.3 Virtual under OpenVZ cannot ping, host lookups, outbound connections while postfix running

  - by Paul Cravey

  My best theory is that some kernel limit is being hit preventing outbound connections. We have tried basically everything from tcpdumps to provisioning an entirely new virtual server (we do not have this problem on any other virtuals), however the problem somehow carried over, even with new postfix build (working). Emails work, and outbound connections work, so long as postfix does not have too much going on. /proc/user_beancounters shows no limits being hit (show below). Nevertheless, pings fail even to IP addresses. TCP stack appears healthy. Load is low. No iowait. Flushed iptables already. Has anyone experienced anything like this? uid resource held maxheld barrier limit failcnt 3: kmemsize 166216365 170262528 9223372036854775807 9223372036854775807 0 lockedpages 0 0 9223372036854775807 9223372036854775807 0 privvmpages 285727 351885 9223372036854775807 9223372036854775807 0 shmpages 16933 17605 9223372036854775807 9223372036854775807 0 dummy 0 0 0 0 0 numproc 150 303 9223372036854775807 9223372036854775807 0 physpages 314156 326191 0 1280000 0 vmguarpages 0 0 9223372036854775807 9223372036854775807 0 oomguarpages 165355 165355 9223372036854775807 9223372036854775807 0 numtcpsock 89 172 9223372036854775807 9223372036854775807 0 numflock 22 76 9223372036854775807 9223372036854775807 0 numpty 1 2 9223372036854775807 9223372036854775807 0 numsiginfo 0 75 9223372036854775807 9223372036854775807 0 tcpsndbuf 2733472 4371752 9223372036854775807 9223372036854775807 0 tcprcvbuf 1798336 5427296 9223372036854775807 9223372036854775807 0 othersockbuf 491120 1000760 9223372036854775807 9223372036854775807 0 dgramrcvbuf 0 238728 9223372036854775807 9223372036854775807 0 numothersock 361 505 9223372036854775807 9223372036854775807 0 dcachesize 135941831 136114679 9223372036854775807 9223372036854775807 0 numfile 2905 4990 9223372036854775807 9223372036854775807 0 dummy 0 0 0 0 0 dummy 0 0 0 0 0 dummy 0 0 0 0 0 numiptent 8 9 9223372036854775807 9223372036854775807 0 [root@bni /]# ping 4.2.2.1 PING 4.2.2.1 (4.2.2.1) 56(84) bytes of data. --- 4.2.2.1 ping statistics --- 9 packets transmitted, 0 received, 100% packet loss, time 8493ms [root@bni /]# service postfix stop [root@bni /]# ping 4.2.2.1 PING 4.2.2.1 (4.2.2.1) 56(84) bytes of data. 64 bytes from 4.2.2.1: icmp_seq=1 ttl=53 time=8.63 ms 64 bytes from 4.2.2.1: icmp_seq=2 ttl=53 time=8.62 ms 64 bytes from 4.2.2.1: icmp_seq=3 ttl=53 time=8.63 ms 64 bytes from 4.2.2.1: icmp_seq=4 ttl=53 time=8.66 ms Outbound connections of all sorts fail when postfix is running.

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• Linux: prevent outgoing TCP flood

  - by Willem

  I run several hundred webservers behind loadbalancers, hosting many different sites with a plethora of applications (of which I have no control). About once every month, one of the sites gets hacked and a flood script is uploaded to attack some bank or political institution. In the past, these were always UDP floods which were effectively resolved by blocking outgoing UDP traffic on the individual webserver. Yesterday they started flooding a large US bank from our servers using many TCP connections to port 80. As these type of connections are perfectly valid for our applications, just blocking them is not an acceptable solution. I am considering the following alternatives. Which one would you recommend? Have you implemented these, and how? Limit on the webserver (iptables) outgoing TCP packets with source port != 80 Same but with queueing (tc) Rate limit outgoing traffic per user per server. Quite an administrative burden, as there are potentially 1000's of different users per application server. Maybe this: how can I limit per user bandwidth? Anything else? Naturally, I'm also looking into ways to minimize the chance of hackers getting into one of our hosted sites, but as that mechanism will never be 100% waterproof, I want to severely limit the impact of an intrusion. Cheers!

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• TCPDump and IPTables DROP by string

  - by Tiffany Walker

  by using tcpdump -nlASX -s 0 -vvv port 80 I get something like: 14:58:55.121160 IP (tos 0x0, ttl 64, id 49764, offset 0, flags [DF], proto TCP (6), length 1480) 206.72.206.58.http > 2.187.196.7.4624: Flags [.], cksum 0x6900 (incorrect -> 0xcd18), seq 1672149449:1672150889, ack 4202197968, win 15340, length 1440 0x0000: 4500 05c8 c264 4000 4006 0f86 ce48 ce3a E....d@[email protected].: 0x0010: 02bb c407 0050 1210 63aa f9c9 fa78 73d0 .....P..c....xs. 0x0020: 5010 3bec 6900 0000 0f29 95cc fac4 2854 P.;.i....)....(T 0x0030: c0e7 3384 e89a 74fa 8d8c a069 f93f fc40 ..3...t....i.?.@ 0x0040: 1561 af61 1cf3 0d9c 3460 aa23 0b54 aac0 .a.a....4`.#.T.. 0x0050: 5090 ced1 b7bf 8857 c476 e1c0 8814 81ed P......W.v...... 0x0060: 9e85 87e8 d693 b637 bd3a 56ef c5fa 77e8 .......7.:V...w. 0x0070: 3035 743a 283e 89c7 ced8 c7c1 cff9 6ca3 05t:(>........l. 0x0080: 5f3f 0162 ebf1 419e c410 7180 7cd0 29e1 _?.b..A...q.|.). 0x0090: fec9 c708 0f01 9b2f a96b 20fe b95a 31cf ......./.k...Z1. 0x00a0: 8166 3612 bac9 4e8d 7087 4974 0063 1270 .f6...N.p.It.c.p What do I pull to use IPTables to block via string. Or is there a better way to block attacks that have something in common? Question is: Can I pick any piece from that IP packet and call it a string? iptables -A INPUT -m string --alog bm --string attack_string -j DROP In other words: In some cases I can ban with TTL=xxx and use that should an attack have the same TTL. Sure it will block some legit packets but if it means keeping the box up it works till the attack goes away but I would like to LEARN how to FIND other common things in a packet to block with IPTables

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• Small TCP Window on WAN between 2 Locations

  - by Brent

  Site A: Denver datacenter. 60MBPS. Site B: Chicago. 100MBPS. ICMP pings: Packets: Sent = 176, Received = 176, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 74ms, Maximum = 94ms, Average = 75ms File transfer between sites that never goes past ~7MBPS: Windows Update download at 60MBPS+: Site to site: IPSec VPN using two Cisco 5520's. CPU at 3-4% and lots of memory to spare. The latency between to two sites is very acceptable so I can't see an issue why it is performing so slow when transferring between the two sites. I have found that any type of transfer (FTP, HTTP, Windows file shares) will never go above ~7MBPS. When the WAN was first setup, I was able to get transfers at 50-60MBPS, which is what is expected due to the WAN connection at the Site A at 60MBPS. Then a few days later, I was not able to get anything going faster than ~7MBPS. Is there a upstream router between Denver and Chicago causing this? I want to take the blame away from our setup as downloads from Windows Update go blazing fast and for the first few days after the site to site VPN came up, I was transferring VM images at 50-60MBPS. Our stack: HP P2000 MSA - HP C7000 Chassis - HP Flex-10 - Cisco Gigabit switch - Cisco ASA - WAN

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• Nagios check_host_alive and check_ping not showing host as down

  - by Kyle

  I am using the check_host_alive command to send 5 packets every minute to all my routers at remote locations. I noticed today I received a notification from The AT&T Global Client Support Center that a router was down (which can take 5-30 minutes to send these notices out) and never received a notice from Nagios. I went onto Nagios and it is was showing the host as alive with a latency of 0ms. This tells me it is seeing the automated response from my router in the data center that, "TTL expired in transit" as a reply from the remote router. Is there anyway for me to tell nagios to check where the reply is comming from? I feel like other people have to of had this issue... I tested it with the check_ping command and it produced the same results. I have the command defined has %hostname% and the proper IP in the host definition, and it works fine for telling me the latency is high. Any ideas are welcome, I have already exercised my Google skills with no results. EDIT: root@IM-UBTU:/# /usr/local/nagios/libexec/check_ping -H 192.168.250.1 -w 100.0,10% -c 200.0,20% -vvv CMD: /bin/ping -n -U -w 10 -c 5 192.168.250.1 Output: PING 192.168.250.1 (192.168.250.1) 56(84) bytes of data. Output: From 10.69.10.2 icmp_seq=1 Time to live exceeded It knows something is wrong why doesn't it give me a warning?

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• DNS issue on Fedora 12? wget wordpress.org fails where wget www.google.com works

  - by Tom Auger

  I'm administering a Fedora 12 box, but am quite new to networking specifics. Recently one of our WordPress apps hosted on our server has stopped being able to perform its auto-update or auto-download of plugins. Investigating further, I have tried the following: $ wget wordpress.org --2010-12-17 11:26:50-- http://wordpress.org/ Resolving wordpress.org... failed: Temporary failure in name resolution. wget: unable to resolve host address âwordpress.orgâ Whereas: $ wget www.google.com --2010-12-17 11:27:26-- http://www.google.com/ Resolving www.google.com... 74.125.226.82, 74.125.226.84, 74.125.226.80, ... Connecting to www.google.com|74.125.226.82|:80... connected. HTTP request sent, awaiting response... 302 Found Location: http://www.google.ca/ [following] --2010-12-17 11:27:26-- http://www.google.ca/ Resolving www.google.ca... 173.194.32.104 Connecting to www.google.ca|173.194.32.104|:80... connected. HTTP request sent, awaiting response... 200 OK Length: unspecified [text/html] Saving to: âindex.html.4â [ <=> ] 9,079 --.-K/s in 0.02s 2010-12-17 11:27:26 (462 KB/s) - âindex.html.4â Interestingly: $ ping wordpress.org PING wordpress.org (72.233.56.138) 56(84) bytes of data. 64 bytes from wordpress.org (72.233.56.138): icmp_seq=1 ttl=50 time=81.5 ms 64 bytes from wordpress.org (72.233.56.138): icmp_seq=2 ttl=50 time=67.3 ms ^C --- wordpress.org ping statistics --- 2 packets transmitted, 2 received, 0% packet loss, time 1783ms rtt min/avg/max/mdev = 67.361/74.448/81.536/7.092 ms and $ nslookup wordpress.org Server: 192.168.2.1 Address: 192.168.2.1#53 Non-authoritative answer: Name: wordpress.org Address: 72.233.56.138 Name: wordpress.org Address: 72.233.56.139 nscd has been stopped and flushed. iptables appear to be clean. At this point I have exhausted my limited abilities to diagnose the issue. Can anyone suggest a resolution path?

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• SNMP Access on Ubuntu

  - by javano

  I am trying to use SNMP to monitor a machine locally on its self and remotely. This is the snmpd.conf (Ubuntu 8.04.1): # sec.name source comunity com2sec readonly 1.2.3.4 nicenandtight com2sec readonly 5.6.7.8 reallysafe group MyROGroup v1 readonly group MyROGroup v2c readonly group MyROGroup usm readonly view all included .1 view system included .iso.org.dod.internet.mgmt.mib-2.system access MyROGroup "" any noauth exact all none none syslocation my house syscontact me <[email protected]> exec .1.3.6.1.4.1.2021.7890.1 distro /usr/bin/distro smuxpeer .1.3.6.1.4.1.674.10892.1 includeAllDisks 95% 1.2.3.4 is the local machines IP and everything is working locally. 5.6.7.8 is the remote machine and initially I am just trying to touch SNMPD with snmpwalk from the remote machine; snmpwalk -v 2c -c reallysafe 1.2.3.4 Timeout: No Response from 1.2.3.4 I have added to iptables as the very first rule; -A INPUT -p udp -m udp --dport 161 -j ACCEPT With such a loose iptables rule I can't see why I can't even touch the SNMPD on that Uubuntu Machine. There are more specific rules further down the table but as I couldn't connect I added the above. TCPDump shows the UDP packets coming in. What could be going wrong here?

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• Should I expect ICMP transit traffic to show up when using debug ip packet with a mask on a Cisco IOS router?

  - by David Bullock

  So I am trying to trace an ICMP conversation between 192.168.100.230/32 an EZVPN interface (Virtual-Access 3) and 192.168.100.20 on BVI4. # sh ip access-lists 199 10 permit icmp 192.168.100.0 0.0.0.255 host 192.168.100.20 20 permit icmp host 192.168.100.20 192.168.100.0 0.0.0.255 # sh debug Generic IP: IP packet debugging is on for access list 199 # sh ip route | incl 192.168.100 192.168.100.0/24 is variably subnetted, 2 subnets, 2 masks C 192.168.100.0/24 is directly connected, BVI4 S 192.168.100.230/32 [1/0] via x.x.x.x, Virtual-Access3 # sh log | inc Buff Buffer logging: level debugging, 2145 messages logged, xml disabled, Log Buffer (16384 bytes): OK, so from my EZVPN client with IP address 192.168.100.230, I ping 192.168.100.20. I know the packet reaches the router across the VPN tunnel, because: policy exists on zp vpn-to-in Zone-pair: vpn-to-in Service-policy inspect : acl-based-policy Class-map: desired-traffic (match-all) Match: access-group name my-acl Inspect Number of Half-open Sessions = 1 Half-open Sessions Session 84DB9D60 (192.168.100.230:8)=>(192.168.100.20:0) icmp SIS_OPENING Created 00:00:05, Last heard 00:00:00 ECHO request Bytes sent (initiator:responder) [64:0] Class-map: class-default (match-any) Match: any Drop 176 packets, 12961 bytes But I get no debug log, and the debugging ACL hasn't matched: # sh log | inc IP: # # sh ip access-lists 198 Extended IP access list 198 10 permit icmp 192.168.100.0 0.0.0.255 host 192.168.100.20 20 permit icmp host 192.168.100.20 192.168.100.0 0.0.0.255 Am I going crazy, or should I not expect to see this debug log? Thanks!

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• Ubuntu 12.04 open port 80 inside WLAN

  - by Eduard

  I have an nginx server running on ubuntu 12.04 that serves http through port 80 and https through port 443. Everything works fine if I access it from the same computer via localhost, 127.0.0.1 or the local IP 192.168.0.11. If I try to access the server from another computer in the same VLAN it does not work for http; it works for https. I have changed my nginx configuration to also listen to port 8000 for http; I can then access http from the other computer in the same VLAN via "http://192.168.0.11:8000". I also have a web server running on port 80 on a windows machine and can access it from another device in the same VLAN, therefore the router is not blocking incoming http traffic. The nginx process is run by root. I have used tcpdump and I see that packets are arriving to Ubuntu: 192.168.0.16.49735 192.168.0.11.80 and that some response is being given 192.168.0.11.80 192.168.0.16.49735 (I do not know what the response is though). There is no request arriving at the nginx web server (I have checked the access log). I have iptables empty. I have unsuccessfully tried to find a solution for a long time to this, it has now become a matter of happiness or bitterness :).

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