[Babel-users] Babel in Bird 1.6.0

[Ondrej Zajicek]

On Sat, Apr 30, 2016 at 03:15:52PM +0200, Toke Høiland-Jørgensen wrote:
> Baptiste Jonglez <baptiste at bitsofnetworks.org> writes:
>
> While I'm not sure what the purpose of this is (a null update with a
> null router ID with infinity metric and interval?) it *is* technically
> in spec. I think the reason why Bird complains is that Ondrej's cleanup
> of my (admittedly messy) packet parsing code inadvertently moved the
> check for the 0x40 flag inside the case branch for AE_IP6.

Hi

Well, the move was not inadvertent. My understanding of RFC 6126:

   o  if the bit with value 40 hexadecimal is set, then the low-order 8
      octets of the advertised prefix establish a new default router-id
      for this TLV and subsequent Update TLVs in the same packet.

is that such flag clearly cannot be used with address families with
prefix lengths shorter than 8 octets.

Also now it seems to me that even the current code is not valid as it
implicitly assumes that the prefix length is 128 with this flag.
As the spec says 'low-order 8 octets of the advertised prefix' then
if one advertise 2001:DB8:1020:3040:5060:7080::/96, then low-order
8 octets of this *prefix* are 1020:3040:5060:7080 and not
5060:7080:0000:0000.

It seems that when used outside of the scope of obvious application (full
IPv6 address), this flag is not really well specified (and does not make
much sense).

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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