[Xorp-users] Linux IPv6 MR

Pavlin Radoslavov pavlin at icir.org
Tue May 23 23:53:04 PDT 2006


> I have a GNU/Linux router with 8 NICs doing routing
> for 8 segments of the whole network in my University,
> 1 of those segments is commercial Internet and 1 other
> segment is Internet2.
> 
> All segments are directly connected to this Linux
> router and is working very well with latest kernel
> (2.6.16.18).  I'm using BGP IPv4/IPv6 for importing
> all Internet2 routes and for exporting my routes and
> it also works fine.
> 
> Now I need to do multicast routing so I enabled all
> respecting modules for IPv4/IPv6 in XORP but just
> IPv4 multicast routing works, IPv6 multicast routing
> doesn't work, neither it doesn't show a neighbor nor
> it register as neighbor in the next-hop router.  I
> am using latest USAGI patch.
> 
> The kernel shows this message:
> 
> KERNEL: assertion (newskb->dst) failed at net/ipv6/ip6_output.c (113)

It appears to be a kernel bug. For testing purpose can you try
pim6sd and see whether you can still trigger that bug.
BTW, I believe that mrd6 (the other IPv6 multicast routing
alternative) performs the multicast forwarding in user
space, hence it won't be a good candidate to test the bug.

Also, can you provide some additional info when the assertion is
triggered. E.g., does it happen when the first data packet is
forwarded, etc.

> Does somebody knows the state of IPv6 multicast
> routing in XORP and in Linux kernel?

We have done very limited testing with an older USAGI snapshot.
See the following email for details:
http://mailman.icsi.berkeley.edu/pipermail/xorp-users/2005-November/000901.html


> I'm not a routing expert but would like to know what
> exactly the 'enable-ip-router-alert-option-check'
> option do?  I don't see a difference with true or
> false.  If enabled is much verbose the output.

If it is enabled, then certain PIM-SM control packets must have the
IP Router Alert option set to be accepted, otherwise those packets
will be dropped with a warning like:
"RX %s from %s to %s on vif %s: missing IP Router Alert option"

If all appropriate PIM control messages from your PIM-SM neighbors
contain the IP Router Alert message (as specified in the PIM-SM
spec), then you won't see any difference even if you enable the
enable-ip-router-alert-option-check option.

Please let us know if you find anything about the kernel crash.

Pavlin

P.S. BTW, the static RP address in your configuration
(fe80::205:5dff:fe7c:61fd) appears to be a link-local address.
In general, this should be a domain-wide reachable address.



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