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  • Transient network dropout for Xen DomU's

    - by Stephen C
    We've got a CentOS server running a cluster of virtuals. Occasionally the cluster's internal network drops out for a minute or so ... and then comes back. The problem is somehow related to the actual network traffic, but it is not a simple load issue. (The system is generally lightly loaded, and the problem occurs irrespective of actual load.) The setup: CentOS 5.6 on Dom0, various CentOS on the DomU's Hardware - a Dell R710 with a BroadCom NextXpress 2 NIC (sigh) using the latest drivers for the NIC from BroadCom Xen configured to use network-bridge and vif-bridge Some iptable tweaks to route an unrelated port to one of the virtuals. The system has one externally visible IP address, and Dom0 runs an Apache httpd configured with a number of virtual hosts each of which reverse proxies to web servers running on the virtuals. (The virtuals have to be NAT'ed, primarily because we don't have enough allocated public IP addresses.) The symptoms: Works fine most of the time. When someone tries to UPLOAD a large file to one virtuals, the internal network drops out ... for all virtuals: The Dom0 httpd sees a network timeout talking to the backend server on the virtual and reports a 502. A previously established ssh connection from Dom0 to any of the DomU's freezes. Our monitoring shows ping failures for traffic between virtuals. The Xen consoles to the DomU's do not freeze. No log messages in any log files that I can see, on either Dom0 or the DomU's ... apart from the Dom0 httpd logs. After a minute or so, the problem clears by itself. This is 100% reproducible. What we've tried: Downloading, building and installing the latest BNX2 driver on Dom0 Turning off MSI on the NIC - adding "options bnx2 disable_msi=1" to /etc/modprobe.conf Turning off tcp segmentation offload - "ethtool -K eth0 tso off". Sacrificing a black rooster at midnight. I've exhausted all my options apart from switching to KVM ... or slaughtering more roosters. Any suggestions?

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  • Are there any routers supporting client-side VPN?

    - by Andreas Hagen
    What I'm asking for is basically what the title says. I need a router that can forward all the data-traffic it receives through a VPN tunnel. Have Google'd a little but I can't seam to find a topic which the links to potential products still are active. The parameters to the specific VPN it is going to be used with is as follows: Sorry it is in Norwegian, but you should be able recognize the relevant parameters like encryption and such.

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  • How do I configure dual WAN links for failover on a Cisco 891?

    - by Donjo
    I have a Cisco 891 that is going to be connected to 2 WAN links, a DSL connection and a cable connection. I'm not so concerned with load balancing between them because the DSL connection speed is a drop in the bucket when compared to the cable speed though it would be nice if it worked that way. I mainly just want to force all traffic through the cable WAN link unless it goes down. I'm not really sure what feature set I should be researching.

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  • Keep source IP after NAT

    - by John Miller
    Until today I used a cheapy router so I can share my internet connection and keep a webserver online too, while using NAT. Users IP ($_SERVER['REMOTE_ADDR']) was fine, I was seeing class A IPs of users. But as traffic grown up everyday, I had to install a Linux Server (Debian) to share my Internet Connection, because my old router couldn't keep the traffic anymore. I shared the internet via IPTABLES using NAT, but now, after forwarding port 80 to my webserver, now instead of seeing real users IP, I see my Gateway IP (Linux Internal IP) as any user IP Address. How to solve this issue? I edited my post, so I can paste the rules I'm currently using. #!/bin/sh #I made a script to set the rules #I flush everything here. iptables --flush iptables --table nat --flush iptables --delete-chain iptables --table nat --delete-chain iptables -F iptables -X # I drop everything as a general rule, but this is disabled under testing # iptables -P INPUT DROP # iptables -P OUTPUT DROP # these are the loopback rules iptables -A INPUT -i lo -j ACCEPT iptables -A OUTPUT -o lo -j ACCEPT # here I set the SSH port rules, so I can connect to my server iptables -A INPUT -p tcp --sport 513:65535 --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT iptables -A OUTPUT -p tcp --sport 22 --dport 513:65535 -m state --state ESTABLISHED -j ACCEPT # These are the forwards for 80 port iptables -t nat -A PREROUTING -p tcp -s 0/0 -d xx.xx.xx.xx --dport 80 -j DNAT --to 192.168.42.3:80 iptables -t nat -A POSTROUTING -o eth0 -d xx.xx.xx.xx -j SNAT --to-source 192.168.42.3 iptables -A FORWARD -p tcp -s 192.168.42.3 --sport 80 -j ACCEPT # These are the forwards for bind/dns iptables -t nat -A PREROUTING -p udp -s 0/0 -d xx.xx.xx.xx --dport 53 -j DNAT --to 192.168.42.3:53 iptables -t nat -A POSTROUTING -o eth0 -d xx.xx.xx.xx -j SNAT --to-source 192.168.42.3 iptables -A FORWARD -p udp -s 192.168.42.3 --sport 53 -j ACCEPT # And these are the rules so I can share my internet connection iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE iptables -A FORWARD -i eth0:1 -j ACCEPT If I delete the MASQUERADE part, I see my real IP while echoing it with PHP, but I don't have internet. How to do, to have internet and see my real IP while ports are forwarded too? ** xx.xx.xx.xx - is my public IP. I hid it for security reasons.

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  • nginx rule to capture header and append value as query string

    - by John Schulze
    I have an interesting problem I need to solve in nginx: one of the sites I'm building receives inbound traffic on port 80 (and only port 80) which may have a certain header set in the request. If this header is present I need to capture the value of it and append that as a querystring parameter before doing a temporary redirect (rewrite) to a different (secure) server, while passing the paramater and any other querystring params along. This should be very doable, but how!? Many thanks, JS

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  • .NET 4 Shared Hosting

    - by Unknown
    Are there any companies that offer shared .NET 4 hosting? I know its still in beta, but from about hours worth of searching, I only found that ASPHostCentral.com offers it. MaximumASP.com and DiscountASP.net currently only offer sandboxing plans. I don't want to get a dedicated server or VPS since my website has low traffic.

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  • Unable to telnet out on port 25 on windows server 2008

    - by NickGPS
    Hi All, I just setup a Windows 2008 R2 server and am trying to get a basic mail server up and running so that I can send emails from my applications. I setup a virtual SMTP server in IIS6 and tried doing a local telnet to port 25, which seemed to work fine. There were no errors during this stage and I can see the mail message appear in the Queue folder. The problem is that mail never leaves the Queue folder. I then tried to telnet to a remote mail server on port 25 but couldn't connect:- telnet 209.85.227.27 25 Could not open connection to the host, on port 25: Connection failed) I checked my firewall and there is a default setting to allow all outgoing TCP traffic with no restriction. I even setup a specific rule for outgoing port 25 traffic but to no avail. I then ran a SmtpDiag.exe command .\SmtpDiag.exe [email protected] [email protected] and received the following output Searching for Exchange external DNS settings. Computer name is WIN-SERVERNAME. Failed to connect to the domain controller. Error: 8007054b Checking SOA for gmail.com. Checking external DNS servers. Checking internal DNS servers. SOA serial number match: Passed. Checking local domain records. Checking MX records using TCP: gmail.com. Checking MX records using UDP: gmail.com. Both TCP and UDP queries succeeded. Local DNS test passed. Checking remote domain records. Checking MX records using TCP: gmail.com. Checking MX records using UDP: gmail.com. Both TCP and UDP queries succeeded. Remote DNS test passed. Checking MX servers listed for [email protected]. Connecting to gmail-smtp-in.l.google.com [209.85.227.27] on port 25. Connecting to the server failed. Error: 10060 Failed to submit mail to gmail-smtp-in.l.google.com. Is there any other diagnostics I can do to figure out if it's my firewall or something else? I have removed antivirus to make sure that it wasn't causing the problem. Any ideas would be much appreciated.

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  • Bittorrent surveillance/monitoring

    - by Flamewires
    Is there any tool to sniff bittorrent traffic and reassemble data about the torrent? Im looking for file names, peers, tracker address, local IP, etc. This is purely for academic interest in which all parties would be willing participants and therefore please dont upvote responses that talk merely about legal issues with using this kind of approach on a production network. I also am assuming that the torrent connections are unencrypted. Thanks

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  • SSH tunneling hangs with many connections

    - by middleofdreams
    I am forced to use SSH tunneling to access many servers (over 100) via one gateway server. To keep connection alive I am using autossh. Everything works pretty well until there is high traffic (people are connecting to most of the servers at once). then ssh process reaches 12% of cpu (which is configured maximum for separate process) and no connection is working anymore - i have to restart autossh script. What could be the possible reason for that?

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  • Routing all data through an VPN tunnel with ppp

    - by Oliver
    I'm trying to create a VPN tunnel that forwards all data from the local machine to the VPN server. I'm using ppp-2.4.5 for this with the following configuration: pty "pptp <VPNServer> --nolaunchpppd" name <my login name> remotename PPTP usepeerdns require-mppe-128 file /etc/ppp/options.pptp persist maxfail 0 holdoff 5 I have a script in if-up.d with the following content: route del default eth0 route add default dev ppp0 Before starting the VPN tunnel my routing looks like: Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 0.0.0.0 192.168.0.1 0.0.0.0 UG 2 0 0 eth0 127.0.0.0 127.0.0.1 255.0.0.0 UG 0 0 0 lo 192.168.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth0 After starting the tunnel (via pon) it looks like: Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 0.0.0.0 0.0.0.0 0.0.0.0 U 0 0 0 ppp0 12.34.56.1 0.0.0.0 255.255.255.255 UH 0 0 0 ppp0 127.0.0.0 127.0.0.1 255.0.0.0 UG 0 0 0 lo 192.168.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth0 Now the problem is, that the VPN tunnel seems to be looped into itself. If I run ifconfig after a few seconds without any traffic: eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500 inet 192.168.0.10 netmask 255.255.0.0 broadcast 192.168.255.255 ether 00:01:2e:2f:ff:35 txqueuelen 1000 (Ethernet) RX packets 39931 bytes 6784614 (6.4 MiB) RX errors 0 dropped 90 overruns 0 frame 0 TX packets 34980 bytes 7633181 (7.2 MiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 device interrupt 20 memory 0xfbdc0000-fbde0000 ppp0: flags=4305<UP,POINTOPOINT,RUNNING,NOARP,MULTICAST> mtu 1496 inet 12.34.56.78 netmask 255.255.255.255 destination 12.34.56.1 ppp txqueuelen 3 (Point-to-Point Protocol) RX packets 7 bytes 94 (94.0 B) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 782863 bytes 349257986 (333.0 MiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 It states that already over 300 MiB have been send, ppp0 is only online since a few seconds and the connection isn't working anyway. Can someone please help me to fix the routing table, so that the traffic from ppp0 is not send again through ppp0 but instead goes to the remote server?

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  • OpenVPN multiple servers on the same subnet, high availability

    - by andre
    Hey everyone. Let me start by saying that my Linux experience isn't super awesome but I can usually find my way around things easily. Over at work we have an OpenVPN setup that's been due for some improvement for a while now. The main server (tap mode) runs in our office, behind a rather slow DSL connection. The main problem is that, since I'm usually out of the office, every time I want to access something on the virtual network I have to go through that server to get anywhere else. We have two servers up on 100 Mbit connections that we use for development and production purposes, about 3 more servers in the office (one of them behind a different T1 line for VOIP) and about two dozen clients who use the network on a daily basis from various locations. We've had situations where network routing (outside of our control) would not allow people to reach our main OpenVPN server whilst the other locations were connectable. Also any time someone outside the office wants to fetch something from any of the servers (say, a 500 MB code repository), a whopping 20 KB/s download speed is just unacceptable these days (did I mention slow DSL? ok). We had to implement traffic shaping on this server since maxing out this connection was fairly trivial. I had the thought of running two (or more) OpenVPN servers in the network. These would have to have the same subnet though, as our application relies on virtual network's IP addresses for some of its core functionality. The clients would also preferably retain the same IP addresses but that's not vital. For simplicity, lets call the current server office and the second server I'm setting up, cloud. Call the server on the T1 phone. This proved to be rather complex because as soon as I connect to cloud, I cannot see office. Any routes to a server that would go through office also do not work while I'm connected to cloud (no ping, nothing) and vice-versa. There's no rules for iptables that would be blocking the traffic either. Recently I came across this article on linuxjournal but the solution they provide seems to only cover the use of two servers and somewhat outdated (can't even find much documentation, their wiki is offline). They also state that adding more servers would be a complex task. Ideally I would like to keep the existing server office running the virtual network and also run the OpenVPN daemon on the cloud and phone servers (100 Mbit and very reliable connection, respectively) so that we're on safe ground in case of a hardware failure, DSL failure, etc. So, in essence, I'm looking for a highly available OpenVPN solution (fix, patch, hack, tweak, whatever you want to call it) that will accept connections on multiple hosts (2 or more) whilst keeping the same IP address subnet regardless of the server to which you connect to. Thanks for reading and sorry for the long post, I hope it gets the point across :P

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  • How Windows Server routes PTP v2 unicast messages?

    - by Bobb
    If my server is placed in PTP v2 enabled network which has grand master clock. And the switch is PTP aware. The server is W2008R2 (soon to be W2012). I also have PTP v2 software client. How does the master clock messages are getting on with Windows Server? Does it need special PTP-aware NIC or it will be treated as normal networking traffic and the software receives it through regular NIC no problem?

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  • Why can't I connect to remote Microsoft SQL Server through SSH tunnel?

    - by Alexander
    I have at home a D-Link DIR-615 C1 router with DD-WRT. I set up the SSH server on the router, and log on through an SSH2-RSA passphrase-protected key. That router is the gateway between the local network and the internet. One of the computers on that network has Microsoft SQL Server 2008 installed, with TCP/IP protocol enabled through port 1433. I've set up port forwarding on the router, so that remote connections are possible and are, in fact, working (some developers log on remotely without problems). I am part of another network, that has internet access through a proxy server, which only has ports 80 and 443 opened. I can't connect to that MSSQL server on that remote server because 1433 port is closed on this network. I connected (using Putty) through 443 port to my router's SSH server, and set up 2 tunnels. One is for RDP (3389), and it's working. The other is for 1433 port, to connect to the server. I can't connect through the SSH tunnel to the MS SQL Server, neither through telnet, or through GUI clients. Am I missing something? Additional details: on connect, I get this error from SQL Server Management Studio: TITLE: Connect to Server Cannot connect to localhost:14330. ADDITIONAL INFORMATION: A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server) (Microsoft SQL Server, Error: 3) For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&EvtSrc=MSSQLServer&EvtID=3&LinkId=20476 BUTTONS: OK The tunnel is configured like this: L14330 192.168.0.103:1433 192.168.0.103 is the permanent address of the SQL Server on the LAN. I also successfully forwarded TCP traffic of 3389 port to that IP, so tunneling is working to that IP address. When connecting without tunnel, through Microsoft SQL Server Management Studio, using the same method the connection establishes. Too bad my proxy doesn't allow 1433 port traffic, I wouldn't have this headache.

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  • Pros and Cons of Creating an Internal Cerificate Authority

    - by Chad
    What are the pros and cons of spinning up an internal certificate authority (primarily Windows 2003 CA)? We have the need to encypt server-server traffic on a project that has 20+ certificates. We could buy certs from Verisign, but I was thinking that an internal CA might be a better long term solution. So I was looking to the community to provide a pros/cons list of what we might gain (or lose) by hosting our own CA? Thanks in advance for the help.

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  • How to make `rm` faster on ext3/linux?

    - by depesz
    I have ext3 filesystem mounted with default options. On it I have some ~ 100GB files. Removal of any of such files takes long time (8 minutes) and causes a lot of io traffic, which increases load on server. Is there any way to make the rm not as disruptive?

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  • postfix on same server as apache2 mysql php

    - by Sandro Dzneladze
    I've dedicated box that hosts wordpress blog with huge traffic. I need mail functionality for me and 2 other employees. I also need mail send capability for fail2ban and logwatch applications. I don't want to stress this box too much, so I wonder: How scure can postfix be? Will I stress server beyond needed with antivirus and mail filters? and postfix? Server is with 2gb ram, e5600 nothing fancy a simple pc.

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  • How to configure an isa server to allow a OPENvpn client to connect to an outside server?

    - by rmarimon
    I'm trying to configure an ISA server (not really my area of expertise) to allow an openvpn client (in the lan) access to an outside openvpn server (in the wan). The openvpn configuration I'm using has worked everywhere. In fact if I take the client outside the lan where the isa server is located, it works perfectly. Inside the isa server lan nothing. The question is what configuration do I need to put on the isa server to allow openvpn traffic to go through?

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  • List Squid's internal ip:port to external ip:port mapping table

    - by joshperry
    I'm assuming that squid keeps a list of internal ip:port that a request is made on and the matching external ip:port that the request is fulfilled with. In the case of a long transfer, such as a file download, it would be nice to be able to see which internal ip:port is downloading the file. I am able to see the traffic and get the external ip:port that squid is using easily with tcpdump or iptraf but I can't find a way to map this back to an internal ip:port.

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  • Avoid blocked URL's when on VPN from home

    - by Marcus
    When I'm on my home PC and on my company VPN I can't get to sites that my company blocks. Is there a way to get around this? Why do my requests to facebook.com go through the VPN? Can you configure your system to, for instance, not go through the VPN for HTTP traffic?

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  • SSL support with Apache and Proxytunnel

    - by whuppy
    I'm inside a strict corporate environment. https traffic goes out via an internal proxy (for this example it's 10.10.04.33:8443) that's smart enough to block ssh'ing directly to ssh.glakspod.org:443. I can get out via proxytunnel. I set up an apache2 VirtualHost at ssh.glakspod.org:443 thus: ServerAdmin [email protected] ServerName ssh.glakspod.org <!-- Proxy Section --> <!-- Used in conjunction with ProxyTunnel --> <!-- proxytunnel -q -p 10.10.04.33:8443 -r ssh.glakspod.org:443 -d %host:%port --> ProxyRequests on ProxyVia on AllowCONNECT 22 <Proxy *> Order deny,allow Deny from all Allow from 74.101 </Proxy> So far so good: I hit the Apache proxy with a CONNECT and then PuTTY and my ssh server shake hands and I'm off to the races. There are, however, two problems with this setup: The internal proxy server can sniff my CONNECT request and also see that an SSH handshake is taking place. I want the entire connection between my desktop and ssh.glakspod.org:443 to look like HTTPS traffic no matter how closely the internal proxy inspects it. I can't get the VirtualHost to be a regular https site while proxying. I'd like the proxy to coexist with something like this: SSLEngine on SSLProxyEngine on SSLCertificateFile /path/to/ca/samapache.crt SSLCertificateKeyFile /path/to/ca/samapache.key SSLCACertificateFile /path/to/ca/ca.crt DocumentRoot /mnt/wallabee/www/html <Directory /mnt/wallabee/www/html/> Options Indexes FollowSymLinks MultiViews AllowOverride None Order allow,deny allow from all </Directory> <!-- Need a valid client cert to get into the sanctum --> <Directory /mnt/wallabee/www/html/sanctum> SSLVerifyClient require SSLOptions +FakeBasicAuth +ExportCertData SSLVerifyDepth 1 </Directory> So my question is: How to I enable SSL support on the ssh.glakspod.org:443 VirtualHost that will work with ProxyTunnel? I've tried various combinations of proxytunnel's -e, -E, and -X flags without any luck. The only lead I've found is Apache Bug No. 29744, but I haven't been able to find a patch that will install cleanly on Ubuntu Jaunty's Apache version 2.2.11-2ubuntu2.6. Thanks in advance.

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  • How do I prevent TCP connection freezes over an OpenVPN network?

    - by Jason R
    New details added at the end of this question; it's possible that I'm zeroing in on the cause. I have a UDP OpenVPN-based VPN set up in tap mode (I need tap because I need the VPN to pass multicast packets, which doesn't seem to be possible with tun networks) with a handful of clients across the Internet. I've been experiencing frequent TCP connection freezes over the VPN. That is, I will establish a TCP connection (e.g. an SSH connection, but other protocols have similar issues), and at some point during the session, it seems that traffic will cease being transmitted over that TCP session. This seems to be related to points at which large data transfers occur, such as if I execute an ls command in an SSH session, or if I cat a long log file. Some Google searches turn up a number of answers like this previous one on Server Fault, indicating that the likely culprit is an MTU issue: that during periods of high traffic, the VPN is trying to send packets that get dropped somewhere in the pipes between the VPN endpoints. The above-linked answer suggests using the following OpenVPN configuration settings to mitigate the problem: fragment 1400 mssfix This should limit the MTU used on the VPN to 1400 bytes and fix the TCP maximum segment size to prevent the generation of any packets larger than that. This seems to mitigate the problem a bit, but I still frequently see the freezes. I've tried a number of sizes as arguments to the fragment directive: 1200, 1000, 576, all with similar results. I can't think of any strange network topology between the two ends that could trigger such a problem: the VPN server is running on a pfSense machine connected directly to the Internet, and my client is also connected directly to the Internet at another location. One other strange piece of the puzzle: if I run the tracepath utility, then that seems to band-aid the problem. A sample run looks like: [~]$ tracepath -n 192.168.100.91 1: 192.168.100.90 0.039ms pmtu 1500 1: 192.168.100.91 40.823ms reached 1: 192.168.100.91 19.846ms reached Resume: pmtu 1500 hops 1 back 64 The above run is between two clients on the VPN: I initiated the trace from 192.168.100.90 to the destination of 192.168.100.91. Both clients were configured with fragment 1200; mssfix; in an attempt to limit the MTU used on the link. The above results would seem to suggest that tracepath was able to detect a path MTU of 1500 bytes between the two clients. I would assume that it would be somewhat smaller due to the fragmentation settings specified in the OpenVPN configuration. I found that result somewhat strange. Even stranger, however: if I have a TCP connection in the stalled state (e.g. an SSH session with a directory listing that froze in the middle), then executing the tracepath command shown above causes the connection to start up again! I can't figure out any reasonable explanation for why this would be the case, but I feel like this might be pointing toward a solution to ultimately eradicate the problem. Does anyone have any recommendations for other things to try? Edit: I've come back and looked at this a bit further, and have found only more confounding information: I set the OpenVPN connection to fragment at 1400 bytes, as shown above. Then, I connected to the VPN from across the Internet and used Wireshark to look at the UDP packets that were sent to the VPN server while the stall occurred. None were greater than the specified 1400 byte count, so the fragmentation seems to be functioning properly. To verify that even a 1400-byte MTU would be sufficient, I pinged the VPN server using the following (Linux) command: ping <host> -s 1450 -M do This (I believe) sends a 1450-byte packet with fragmentation disabled (I at least verified that it didn't work if I set it to an obviously-too-large value like 1600 bytes). These seem to work just fine; I get replies back from the host with no issue. So, maybe this isn't an MTU issue at all. I'm just confused as to what else it might be! Edit 2: The rabbit hole just keeps getting deeper: I've now isolated the problem a bit more. It seems to be related to the exact OS that the VPN client uses. I have successfully duplicated the problem on at least three Ubuntu machines (versions 12.04 through 13.04). I can reliably duplicate an SSH connection freeze within a minute or so by just cat-ing a large log file. However, if I do the same test using a CentOS 6 machine as a client, then I don't see the problem! I've tested using the exact same OpenVPN client version as I was using on the Ubuntu machines. I can cat log files for hours without seeing the connection freeze. This seems to provide some insight as to the ultimate cause, but I'm just not sure what that insight is. I have examined the traffic over the VPN using Wireshark. I'm not a TCP expert, so I'm not sure what to make of the gory details, but the gist is that at some point, a UDP packet gets dropped due to the limited bandwidth of the Internet link, causing TCP retransmissions inside the VPN tunnel. On the CentOS client, these retransmissions occur properly and things move on happily. At some point with the Ubuntu clients, though, the remote end starts retransmitting the same TCP segment over and over (with the transmit delay increasing between each retransmission). The client sends what looks like a valid TCP ACK to each retransmission, but the remote end still continues to transmit the same TCP segment periodically. This extends ad infinitum and the connection stalls. My question here would be: Does anyone have any recommendations for how to troubleshoot and/or determine the root cause of the TCP issue? It's as if the remote end isn't accepting the ACK messages sent by the VPN client. One common difference between the CentOS node and the various Ubuntu releases is that Ubuntu has a much more recent Linux kernel version (from 3.2 in Ubuntu 12.04 to 3.8 in 13.04). A pointer to some new kernel bug maybe? I'm assuming that if that were so, then I wouldn't be the only one experiencing the problem; I don't think this seems like a particularly exotic setup.

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