[Xen-users] DomU PV network problems

[Sauro Saltini <saltini@xxxxxx>]

Hi everybody.

I've got a strange problem with PV networking on Linux.

My current configuration is :
- Xen 4.0.0
- DOM0 kernel 2.6.31.13
- DOMU kernels either 2.6.31.13 or 2.6.36-rc3 (vanilla)

one of my DomU's is intended to act as a router/firewall for all the 
other ones.
I have configured 2 distinct bridges in Dom0 :
br0 - connects the firewall DomU "external" nic to the external faced 
host NIC (phisical)
br1 - connects the "internal" virtual nic of firewall DomU (eth1) with 
the other DomU's virtual nics.
Each "guest" DomU has defined the firewall DomU's "internal" address as 
default gateway, the firewall by now acts simply as a NAT gateway, with 
ip_forward active and a single NAT rule to SNAT outgoing packets with 
his own external IP.
I've first installed the fw DomU as an hvm domain (nic's = ioemu) with 
slackware 13.0 and tried the whole thing connecting from one of the 
other DomU's to the external network and all worked smoothly.
As soon as I've converted the fw DomU's to a PV domain (using either 
2.6.31.13 or 2.6.36-rc3 kernels with PV drivers) something changed in a 
weird way...
I can still ping the firewall DomU both from "internal" domU's network 
and from the external lan, but packets from a DomU can't reach the 
external network anymore !
Running "tcpdump -nvvi" on both firewall's NICs and pinging an external 
host from one of the other domU's reveals that packets arrive on the 
firewall, are correctly NATted and appear on the external connected 
interface, but then simply disappear !
on Dom0 "tcpdump -nvvi br0" (br0 = external bridge) never shows up any 
traffic !
I've already tried to configure tx checksum offloading = off (ethtool -K 
<nic> tx off) on all the involved interfaces without any success.
Please help...
Many thanks in advance.

Sauro Saltini.

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