Xen devel - Aug 2004 - xen0=2.6.7 network problem in xenU

Now that i''ve finally got another domain booting on my 2.6.7 xen
server, I can''t seem to get networking going in a xenU (2.6.7 also)
domain.

the xenU domain receives packets just fine (only broadcast and multicast though
as it can''t respond to arp requests), but can''t transmit
anything. Even by manually adding the arp entry, nothing still gets sent. A
tcpdump in the xen0 domain doesn''t show any packets coming out of xenU,
and the counters on eth0 in xenU aren''t incrementing for sent packets.

Any ideas? this is an identical xenU domain that was running fine on my other
server.

thanks

James

hmmm... loading the ipv6 module caused this problem. I think maybe i''ve
seen that before too.

Can someone please test a 2.6.7-xen0 kernel with ipv6 loaded and then a
2.6.7-xenU kernel in another domain and see if they can get any network traffic?

thanks

James



From: James Harper
Sent: Mon 23/08/2004 3:10 PM
To: xen-devel@lists.sourceforge.net
Subject: [Xen-devel] xen0=2.6.7 network problem in xenU


Now that i''ve finally got another domain booting on my 2.6.7 xen
server, I can''t seem to get networking going in a xenU (2.6.7 also)
domain.

the xenU domain receives packets just fine (only broadcast and multicast though
as it can''t respond to arp requests), but can''t transmit
anything. Even by manually adding the arp entry, nothing still gets sent. A
tcpdump in the xen0 domain doesn''t show any packets coming out of xenU,
and the counters on eth0 in xenU aren''t incrementing for sent packets.

Any ideas? this is an identical xenU domain that was running fine on my other
server.

thanks

James

> hmmm... loading the ipv6 module caused this problem. I think maybe
i''ve seen that before too.
Our netfront/netback drivers should be transparent to the actual
protocol that you''re running over them. 

We''ve never tested them with ipv6, but I''d be kinda surprised
if
they were at fault.

I wander if this is some sort of ipv6 interaction with either the
bridge or ebtables code? I''d wager that they haven''t been well
tested with ipv6.
 
> Can someone please test a 2.6.7-xen0 kernel with ipv6 loaded and then a
2.6.7-xenU kernel in another domain and see if they can get any network traffic?
Is it just the act of having the module installed that break
things, or do you need to configure one of the two domains with
an ipv6 interface address? 

Ian


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I probably should clarify, I can''t get xenU to talk on the network in
any way (it listens but doesn''t talk) when xen0 has the ipv6 module
loaded.

simply having the ipv6 module there in dom0 seems to break things

james



From: Ian Pratt
Sent: Mon 23/08/2004 7:41 PM
To: James Harper
Cc: xen-devel@lists.sourceforge.net; Ian.Pratt@cl.cam.ac.uk
Subject: Re: [Xen-devel] xen0=2.6.7 network problem in xenU (SOLVED)

> hmmm... loading the ipv6 module caused this problem. I think maybe
i''ve seen that before too.
Our netfront/netback drivers should be transparent to the actual
protocol that you''re running over them. 

We''ve never tested them with ipv6, but I''d be kinda surprised
if
they were at fault.

I wander if this is some sort of ipv6 interaction with either the
bridge or ebtables code? I''d wager that they haven''t been well
tested with ipv6.
 
> Can someone please test a 2.6.7-xen0 kernel with ipv6 loaded and then a
2.6.7-xenU kernel in another domain and see if they can get any network traffic?
Is it just the act of having the module installed that break
things, or do you need to configure one of the two domains with
an ipv6 interface address? 

Ian

> I probably should clarify, I can''t get xenU to talk on the network
in any way (it listens but doesn''t talk) when xen0 has the ipv6 module
loaded.
> 
> simply having the ipv6 module there in dom0 seems to break things
What happens if you run "tcpdump -ni vifX.X" in domain 0. Do you
see any packets being sent from the other domain?

What about packet count statistics if you do "ifconfig vifX.X"?
Does the receive count go up? Are there any errors or drops?

It''s really hard to imagine how either our netfront or netback
drivers could not be totally transparent to protocol.

ebtables or bridge code has to be the prime suspect. This will be
confirmed if the tcpdump''ing the vif shows packets. 

If packets aren''t showing up, try enabling the debug printf''s
in
netback/common.h and netfront.c

Ian



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a tcpdump in dom0 doesn''t show any packets coming out of the vif
interfaces. Not even the arp requests. The packet counts don''t
increment when I sent packets, although they do otherwise increment occasionally
but I don''t know why.

if i do a flood ping (ping -f), i get lots of dots but obviously it
doesn''t know the mac address (actually it does sometimes because it can
listen and so hears some arp responses). If I add in the mac address manually, i
get about 14 dots and then nothing. almost like it''s filling up a queue
somewhere and then stops.

Are you able to reproduce this at all? i''m not able to test it for a
few days and I don''t need ipv6 anyway.

James



From: Ian Pratt
Sent: Tue 24/08/2004 7:43 AM
To: James Harper
Cc: Ian Pratt; xen-devel@lists.sourceforge.net; Ian.Pratt@cl.cam.ac.uk
Subject: Re: [Xen-devel] xen0=2.6.7 network problem in xenU (SOLVED)

> I probably should clarify, I can''t get xenU to talk on the network
in any way (it listens but doesn''t talk) when xen0 has the ipv6 module
loaded.
> 
> simply having the ipv6 module there in dom0 seems to break things
What happens if you run "tcpdump -ni vifX.X" in domain 0. Do you
see any packets being sent from the other domain?

What about packet count statistics if you do "ifconfig vifX.X"?
Does the receive count go up? Are there any errors or drops?

It''s really hard to imagine how either our netfront or netback
drivers could not be totally transparent to protocol.

ebtables or bridge code has to be the prime suspect. This will be
confirmed if the tcpdump''ing the vif shows packets. 

If packets aren''t showing up, try enabling the debug printf''s
in
netback/common.h and netfront.c

Ian

On Tue, 24 Aug 2004, James Harper wrote:
> a tcpdump in dom0 doesn''t show any packets coming out of the vif
> interfaces. Not even the arp requests. The packet counts don''t
increment
> when I sent packets, although they do otherwise increment occasionally
> but I don''t know why.
I''m not seeing dhcp requests come out, but if I give the
interface an IP address by hand things seem to work fine.

-- 
"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it." - Brian W. Kernighan



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> On Tue, 24 Aug 2004, James Harper wrote:
> 
> > a tcpdump in dom0 doesn''t show any packets coming out of the
vif
> > interfaces. Not even the arp requests. The packet counts
don''t increment
> > when I sent packets, although they do otherwise increment occasionally
> > but I don''t know why.
> 
> I''m not seeing dhcp requests come out, but if I give the
> interface an IP address by hand things seem to work fine.
Did you enable ''vif-antispoof'' in your xend-config.sxp?

If enabled, this inserts some iptables rules that ensures that
only packets with a specified IP source address will be forwarded
from a given vif. It basically ensures that a domain can only use
the IP address it''s been allocated and can''t spoof others.

The iptables rules attempt to let DHCP requests through (where
the IP src address will be unset), but hasn''t been well tested
and may be overzealous in its filtering (see the vif-bridge
script).

If you have "(vif-antispoof no)" (and have no other iptables
rules inserted) then I''m not sure why DHCP isn''t working. I
believe this is a pretty common usage mode.

BTW: is this using the kernel IP_PNP DCHP, or user space?

Best,
Ian


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On Tue, 24 Aug 2004, Ian Pratt wrote:
> > I''m not seeing dhcp requests come out, but if I give the
> > interface an IP address by hand things seem to work fine.
> 
> Did you enable ''vif-antispoof'' in your xend-config.sxp?
Nah, I''m just hopelessly dumb.  I installed a very minimal
distro inside my disk image - so minimal there weren''t dhcp
tools, and the network startup scripts didn''t complain ;)
> BTW: is this using the kernel IP_PNP DCHP, or user space?
In my case, neither ;)

Installing dhcp utilities fixed the problem.

-- 
"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it." - Brian W. Kernighan



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