[Babel-users] Babel MAC auth fails due to packet reordering

[Daniel Gröber]

Hi babel-users,

I'm seeing babel mac authentication failures related to the packet counter
on a wireless link. I've tracked this down to being because of packet
reordering. Wireshark packet traces on both sides look something like this:

Sender:

    Src     Dst       PC
    fe80::1 fe80::2   1452  Babel router-id update update update pc hmac
    fe80::1 ff02::1:6 1453  Babel hello pc hmac
    fe80::1 fe80::2   1454  Babel ihu pc hmac

Receiver:

    fe80::1 fe80::2   1452  Babel router-id update update update pc hmac
    fe80::1 fe80::2   1454  Babel ihu pc hmac
    fe80::1 ff02::1:6 1453  Babel hello pc hmac

AFAICT babeld shares the packet counter across unicast and multicast
hellos, however since these constitute different flows it seems reasonable
for something in the network stack to reorder them.

A quick skimming of RFC 7298 suggests the PC is indeed intended to be
per-interface without taking the {mult,un}icast bit into account. Is this
an oversight in the spec?

--Daniel