Re: [babel] proposed info model change

Juliusz Chroboczek <jch@irif.fr> Fri, 26 February 2021 19:22 UTC

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From: Juliusz Chroboczek <jch@irif.fr>
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Subject: Re: [babel] proposed info model change
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> FROM
> The router-id value MUST NOT consist of all zeroes or all ones.
> TO
> The router-id value MUST be unique among all instances of Babel on a device.

RFC 8966 Section 4.1.3 says:

   A router-id is an arbitrary 8-octet value.  A router-id MUST NOT
   consist of either all binary zeroes (0000000000000000 hexadecimal) or
   all binary ones (FFFFFFFFFFFFFFFF hexadecimal).

The rationale for that is that an all-zero value is useful as an internal
sentinel value, e.g. in order to mark that the router-id is not known
or that a data structure hasn't been initialised yet.

As to unicity, Babel assumes that router-ids are unique.  More exactly,
bad things will happen if the same prefix is announced by two routers with
the same router-id unless seqnos are synchronised.  I believe that you may
safely assume unicity, at least until such time when people try to
optimise the protocol by synchronising seqnos between distinct routers.