[Bug 197344] tx checksum broken on XEN

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=197344

            Bug ID: 197344
           Summary: tx checksum broken on XEN
           Product: Base System
           Version: 10.1-RELEASE
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: pgadmin at pse-consulting.de

This issue might be related to
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=192013 and
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=154428 , but I found it to be
NOT pf specific.

I've been testing pfSense 2.2 on Xen 4.1, and got the same issue as
https://forum.pfsense.org/index.php?topic=85797.15 : routing traffic through
the FreeBSD 10.1 machine that uses xn* interface hardly works and gives abysmal
performance. Packets leaving the router contain an invalid checksum, and don't
reach the target VM's tcp stack.

A workaround (with at least 50% performance penalty) is to disable tx
offloading on all router interfaces in dom0, i.e. calling 

ethtool -K vif{N}.{x} tx off

The issue can be observed whether the pf firewall is active or not, so it
appears to be a FreeBSD xen-netfront driver problem.

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