IPv6 BFD interop with Huawei, checksum 0 UDP

[Maria Matejka]

Hello!

On Wed, Jun 12, 2024 at 06:32:10PM +0700, Ville O wrote:

> At least some Huawei devices use a checksum of 0 for all IPv6 BFD UDP
> packets after finishing Poll/Final.
> All packets sent with states other than Up or with flags other than C
> have the correct checksums.
>
> [...]
> 
> This issue could be worked around on the BIRD side at least on the
> Linux platform.
> RFC6936 allows [3] for hosts to enable accepting IPv6 UDP with a
> checksum of 0 and this is implemented in Linux kernels from 3.16 with
> sockopt "UDP_NO_CHECK6_RX".
> I have tested that this indeed works: checksum 0 packets are received
> to AF_INET6, SOCK_DGRAM sockets when it is enabled.
> 
> I wonder if it would be acceptable to enable this option on the IPv6
> socket(s) used for BFD in BIRD, if supported by the platform?

Patches welcome. It should be configurable and off by default. For more
information on how to contribute, see the contributing guidelines:

    https://gitlab.nic.cz/labs/bird/-/blob/master/CONTRIBUTING.md

Thank you for raising awareness about this issue.

Maria

-- 
Maria Matejka (she/her) | BIRD Team Leader | CZ.NIC, z.s.p.o.
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