rfc1583compat

[Ondrej Zajicek]

On Mon, Nov 22, 2010 at 02:46:10PM +0100, Petr Šťastný wrote:
>    Hello,
> 
>    what is the exact meaning of rfc1583compat switch in OSPF protocol a what
>    is the appropriate difference in route table calculation?

There are two changes caused by rfc1583compat switch:

1) A subtle and tricky change in computing inter-area routes (or
external routes from other areas, i forgot some details). This change is
well described in RFC 2328 (RFC1583Compatibility flag). To get better
understanding of that issue, i would also suggest to read relevant parts 
of RFC 1583 and RFC 2178 (where the problem with the old behavior is
better explainted than in RFC 2328). Essentially, there was a bug in the
OSPF algorithm in RFC 1583, which was (incompletely) fixed (in an
incompatible way) in RFC 2328 and later (hope completely) fixed in RFC
2328. This flag forces to use original alg from RFC 1583.

2) There is also a BIRD-specific change in assigning LSA IDs for
summary and external LSAs. With rfc1583compat, it is assigned in
a way that is compatible with even older RFC 1247, but does not
allow external (and summary) routes for nested subnets.
See a comment in proto/ospf/topology.c in fibnode_to_lsaid()
function for details.


So, unless you really need some compatibility with some really archaic
implementation, do not enable rfc1583compat. My advice is also not to
use multiple OSPF areas at all.

-- 
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."
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 197 bytes
Desc: Digital signature
URL: <http://trubka.network.cz/pipermail/bird-users/attachments/20101122/9588a0d4/attachment-0001.asc>