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Xen networking problem
This is a discussion on Xen networking problem within the XEN forums, part of the Linux virtualization category; Hello, We are experiencing a very strange networking problem with the open source version of Xen. The host OS was ...
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07-02-2008, 11:30 PM
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Xen networking problem
Hello,
We are experiencing a very strange networking problem with the open source version of Xen. The host OS was CentOS 5.1, but I believe it has been patched to the latest version. We are using the Xen virtualization that ships with CentOS. The Ubuntu guest VM is running 7.1.2008 When the Ubuntu guest VM boots up, it exhibits the following behavior: The VM can ping its default gateway The VM can ping remote hosts by IP address The VM can run nslookup, connect to both local and remote DNS servers, and successfully resolve names (so, UDP is working…) The host OS can SSH into the VM (both are on the same logical subnet) The VM can SSH into the host OS The VM cannot do any kind of TCP based connections to hosts other than the host OS. We have tried FTP, HTTP, and SSH. It should also be noted that we attempted to perform an installation of a CentOS 5.1 VM using the CD to boot and then selecting HTTP and FTP downloads from known mirrors. These TCP transactions also failed, so the problem doesn’t appear to be specific to the Ubuntu VM. I ran a tcpdump of the virtual bridge interface and I can see outbound TCP connections and the return traffic. But for some reason the return traffic isn’t being passed on to the VM. I tried disabling IPTables on the host OS and that didn’t impact anything. It should also be noted that Xen worked perfectly on another CentOS 5.1 server. The problem is showing up only on some new SuperMicro servers that my customer purchased. Any help would be greatly appreciated! Here is the uname –an output of the host OS: Linux sf-prod-host2.keystream.com 2.6.18-92.1.6.el5xen #1 SMP Wed Jun 25 14:13:10 EDT 2008 x86_64 x86_64 x86_64 GNU/Linux Here is the Xen config file: (logfile /var/log/xen/xend.log) (loglevel DEBUG) (xend-unix-server ye  (xend-unix-path /var/lib/xend/xend-socket) (xend-relocation-hosts-allow '^localhost$ ^localhost\\.localdomain$') (network-script network-bridge) (vif-script vif-bridge) (dom0-min-mem 256) (dom0-cpus 0) Here is the test.cfg file used to launch the VM: kernel = '/boot/vmlinuz-2.6.22-14-xen' ramdisk = '/boot/initrd.img-2.6.22-14-xen' memory = '4096' name = "test" cpus = "" # leave to Xen to pick vif = [ "mac=00:16:3e:77:b8:a4,bridge=xenbr0" ] root = '/dev/hda1 ro' disk = ['tap:aio:/xen/test/disk.img,hda1,w','tap:aio:/xen/test/swap.img,hda2,w'] extra = "4" on_poweroff = 'destroy' on_reboot = 'restart' on_crash = 'restart' extra = 'xencons=tty' 
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