kern/166645: virtio rxcsum breaks checksum for local linux hosts IPv6 TCP

[Arne Schwabe]

>Number:         166645
>Category:       kern
>Synopsis:       virtio rxcsum breaks checksum for local linux hosts IPv6 TCP
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Wed Apr 04 16:10:01 UTC 2012
>Closed-Date:
>Last-Modified:
>Originator:     Arne Schwabe
>Release:        FreeBSD 9.0-RELEASE amd64
>Organization:
University of Paderborn
>Environment:
FreeBSD mail.blinkt.de 9.0-RELEASE FreeBSD 9.0-RELEASE #0: Tue Jan 3 07:46:30 UTC 2012 root at farrell.cse.buffalo.edu:/usr/obj/usr/src
/sys/GENERIC amd64
>Description:
When using rxsum, tcp checksum from offladed ipv6 packets of local kvm guest are incorrect and are thrown away. TCP4 connections work fine. 


>How-To-Repeat:
Setup a ubuntu precise 64 bit machine with kvm and a FreeBSD 9 machine both with virtio drivers. Connect them both to a bridge device (br0) which is connected to an external device (a bond0 device in this case).

Do a telnet -6 fbsd ssh from the linux box. 
>Fix:
Using ifconfig vtnet0 -rxcsum solves the problem.

>Release-Note:
>Audit-Trail:
>Unformatted: