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Date: Mon, 23 Jun 2014 11:42:01 +0100
From: Karl Pielorz <kpielorz_lst@tdx.co.uk>
To: freebsd-net@freebsd.org
Subject: Weird Xen networking issue with PV interfaces passing traffic to
 other PV's...
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Hi,

I originally posted to freebsd-xen about this (and I've raised a PR) 
-pr188261 - <https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=188261>

It's been suggested I should ask in FreeBSD-NET to see if someone can look 
at this, and suggest how to proceed...

In a nutshell - the FreeBSD PV network code won't pass packets properly if 
you setup two VM's on the same XenServer trying to use one of the VM's as a 
'router' (i.e. passing traffic). Swap it for linux - works. Disable PV - 
works - anyway, the details are in the PR.

If anyone has a chance to look at that and suggest what I can do to try and 
debug this further? - I've done packet captures from the VM's (they show a 
lot of retransmits) - but I'm not sure how I can go any further in look at 
this - or what the problem is likely to be (it's been suggested it's 
checksum related - which '-txcsum' seems to address for clients, but not 
the  router).

If some kind soul can have a look at this - and suggest anything?

Cheers,

-Karl