[Xorp-hackers] question on MLD querier -- rtalert extension header?

Kevin Fall kfall at cs.berkeley.edu
Mon Jul 7 21:09:53 PDT 2008


Ok, this took me most of the day (unfortunately), but here it is:

I am running on a Redhat linux system, and my problem was due to the  
issue discussed here:

http://sourceware.org/bugzilla/show_bug.cgi?id=5760

Basically, inet6_opt_init() was setting the v6 extension header length  
to the value 1 instead of 0, even for small
extensions like the HBH/RtAlert one.

This is wrong.  But the consequence is that the apparent size of the  
option + cmsg structure was
too big.  If cmsg_len is appropriately trimmed to the option size  
based on
return values of inet_opt_XX, then the kernel (correctly) gives an  
EINVAL because it thinks
the option is longer than the ancillary data provided to hold it :(.

Attached is the .config for you.  I'm looking into the best way to fix  
this, but it would appear
that verifying and whacking as necessary the header produced by  
inet6_opt_init would be a first step.

thx,

- K
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On Jul 7, 2008, at Jul 712:22 AMPDT, Pavlin Radoslavov wrote:

>> It appears to me that MLD query messages do not include the HBH/ 
>> Router-
>> Alert extension header.  I believe this is incorrect.
>> (queries need to be processed by non-querier multicast routers on the
>> same subnet).  Can somebody very/explain whether
>> I have this correct?
>
> Yes, all MLD messages must include the IPv6 Router Alert option.
> I just tested it on FreeBSD-7.0, and the Query messages actually
> include the Router Alert extension header, so the problem is
> probably OS-specific.
>
> If this option is missing in your setup, then this is a bug. In that
> case please submit a Bugzilla entry with information how to
> reproduce the problem, OS version, etc.
>
> Pavlin
> (still waiting for your .config Linux kernel config file :)
>



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