Xen: Dom0 and DomU can ping, but no other network connectivity – checksum problems

This appears to be a long standing bug with Xen which has not yet been fixed, it has shown its face in a few of our servers recently – but not all.  Basically once Xen is installed on Dom0 you are able to ping it, however anything other network services do not work, such as SSH.  From what I have read this is due to checksums being done in numerous places, and seems that there is a bug somewhere while this is being done which results in the checksums not matching, and the packets being dropped.   The solution to this is to run the following:

ethtool -K eth0 tx off

This same issue arises in the DomUs (Guest) , and the same fix can be used.  Its probably a good idea to place in /etc/rc.local on Redhat/Centos/Fedora systems.

Filed under: Uncategorized by — aaron @ 11:20 pm

Xen: How to check if Intel VT is enabled?

This method can be used to check if Intel VT is running in any Linux distribution including when you are running Xen.  Its easier than having to reboot, especially if the server is active!

cat /proc/cpuinfo

Check for the vmx flag, an example is as follows:

processor       : 7
vendor_id       : GenuineIntel
cpu family      : 6
model           : 23
model name      : Intel(R) Xeon(R) CPU           E5410  @ 2.33GHz
stepping        : 6
cpu MHz         : 2333.410
cache size      : 6144 KB
physical id     : 7
siblings        : 1
core id         : 0
cpu cores       : 1
fpu             : yes
fpu_exception   : yes
cpuid level     : 10
wp              : yes
flags           : fpu tsc msr pae mce cx8 apic mtrr mca cmov pat pse36 clflush d                                   ts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl                                    vmx est tm2 cx16 xtpr lahf_lm
bogomips        : 5836.28
clflush size    : 64
cache_alignment : 64
address sizes   : 38 bits physical, 48 bits virtual
power management:

Filed under: Uncategorized by — aaron @ 10:15 pm