RE: IPv6 return path filter default active?

Hi Igor,

Thanks for your help and time!

> First question: does the router A see the response coming from
> router B and then drop it or does the router B drop the packet?

Router A sees the packets coming in (I see them when I run tcpdump).

> Second question: why don't you configure router A to go through
> router B as a prefered route to access the internet and use VlanY
> as a fallback in case router B gets down?

That is what I think is the nature of using BGP: you get asymmetric
routes, where each router uses the shortest path to the internet, and
the return traffic may come via any router.

> Anayway, as far as I understand your problem, the packet would be 
> returned to router A on a different interface from where it was sent.

That is correct.

> So the interface of your router A will receive a packet from 
> router B but destination IP address is the one of VlanY which
> is not matching the interface getting it and causes the DROP.

Router A should just route the packet to the correct interface/socket.
It does so for ping6...

> You can probably setup an NDP proxy to solve this but it is an 
> ugly solution .

NDP may be necessary when router B does not know where to send a package
(which you can detect by seeing the Neighbour Sollicitation packets).
But router B knows where to send the packages: router A and B share
routes via OSPF, and I see the packages coming in on router A.
The problem must be in router A...
 
> All networking options (including NDP proxy, rpfilter etc.) can be
> find here http://kernel.org/doc/Documentation/networking/ip-sysctl.txt

Thanks for that link, it's more complete than other lists I have found.

-- 
Best regards,
Reinier Boon


Reinier Boon | Senior software engineer | Telecats bv | KvK Enschede 06069106 | Tel: +31 53 488 99 26 | Fax: +31 53 488 99 10 | Email: [email protected]