bird6: "Netlink: No such process" error from kernel proto on OSPF multipath prefixes

[Israel G. Lugo]

Hello,

On 27-07-2015 20:57, Ondrej Zajicek wrote:
> The problem here is that Linux IPv6 multipath API is different from the
> IPv4 multipath API and very inconvenient for our purposes.
> 
> AFAIK people from Cumulus Networks are trying to fix this issue directly
> in Linux kernel to have more reasonable API, which would probably make
> BIRD work with some minimal fixes.
> 
> For more details, see slides 15+ in:
> https://www.netdev01.org/docs/prabhu-linux_ipv4_ipv6_inconsistencies_talk_slides.pdf

I see. Indeed there can be some nuisances, especially in cases with
multiple concurrent insertions/deletions, where there might apparently
be duplicate netlink messages.

I found a paper by the same author on this subject, which goes into a
bit more detail on the suggested solutions:

http://people.netfilter.org/pablo/netdev0.1/papers/The-case-for-eliminating-inconsistencies-between-IPv4-and-IPv6-kernel-User-API.pdf

Do you happen to know what is the status of this proposal in the Linux
kernel? I would imagine that it will take a while for these changes to
be available in production, if they are accepted at all.

May I suggest that it might be worthwhile the effort to attempt tackling
this problem in user space, at least for now? The multipath feature does
help a lot, and as it is now we can't really use it (routes are
constantly being added and deleted).

As I understand the problem, this would require some work of keeping the
internal route table in sync with the kernel notifications: detecting
when a notification relates to an already existing prefix and add to to
the internal table as a multihop route, etc. I am not familiar with the
BIRD codebase other than through a cursory glance, but I could try to
think about it a bit. Of course, it would be much easier with your guidance.

I haven't seen how others implemented  this, for example the Quagga
people, but they must have had to deal with it somehow.

Regards,

--
Israel G. Lugo
Núcleo de Redes e Comunicações
Direção de Serviços de Informática
Instituto Superior Técnico

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