Re: [Xen-devel] xen-netfront does not properly transmit forwarded packets

[Jean Baptiste Favre <xen-devel@xxxxxxxxxxx>]

Hello,
I got a similar issue with PCI passthrough (only with 32bits VM, 64bits
runs fine) with only 1 VM which has control on physical network card
(ie. you NetVM).

What if you try to ping from NetVM ?
I do not see echo reply coming in except for some memory amount.

I'm working on finding root cause with Konrad Rzeszutek Wilk and Ian
Campbell. First mail of the thread can be found here:
http://lists.xensource.com/archives/html/xen-devel/2011-01/msg00866.html

Maybe both issues could be related to each other so that we can join our
efforts to solve it ?

Regards,
JB


Le 28/02/2011 11:18, Rafal Wojtczuk a écrit :
> Hello,
> 
> There is a very weird issue with xen-netfront (I think it is the frontend
> problem, not backend). The problem manifests itself with drivers from the 
> SUSE 
> kernel-xen-2.6.34.1; I don't know whether it affects vanilla code as well.
> For completeness, xen is 3.4.3, all 64bit.
> 
> The problem seems to be - xen-netfront does not properly transmit forwarded
> packets (locally generated packets are txed fine).
> 
> The network looks like this (of course eth0s are xen-netfront) :
> 
> testVM             FirewallVM                NetVM
> |  eth0  | <---> | vifF.0 eth0 | <---> | vifN.0 wlan0 | <---> Internet
> 
> If I do "ping someInternetIP" in FirewallVM, "tcpdump -n -i eth0" 
> running in FirewallVM shows outgoing icmp packets, and "tcpdump -n -i vifN.0"
> running in NetVM shows incoming packets - all fine.
> 
> If I do "ping someInternetIP" in testVM, packets arrive fine on vifF.0 and
> are SNATed. Then "tcpdump -n -i eth0" running in FirewallVM shows outgoing 
> icmp 
> packets, BUT "tcpdump -n -i vifN.0" running in NetVM shows NOTHING.
> 
> The important thing is that during the latter experiment, the /proc/interrupts
> line for vifN.0 shows one new interrupt per second - so vifN.0 is notified by
> FirewallVM's eth0 about packet transmission, yet packets are not seen by
> vifN.0. The TX bytes counter for FirewallVM's eth0 increases normally; no 
> errors
> reported by any interface; nothing in the logs.
> 
> In case it matters: there is no bridging used at all, just "bare" vifX.Y. 
> Proxy 
> arp is activated for both vifs. No IP is assigned to vifs. Turning SNAT off
> in FirewallVM does not change anything. The issue has been reproduced by two
> different persons on two different machines.
> 
> Does anyone have an idea why this is happening ? What is the difference in
> frontend's handling of forwarded packets in comparison to locally generated
> ones ? Maybe some function does not work properly in interrupt context ?
> I guess not many people use netfront in a router machine, so this issue may
> have survived unnoticed for a long time.
> 
> Regards,
> RW
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel
> 


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