Support for 4B ASN in BGP

[Ondrej Zajicek]

Hello

On Mon, Oct 06, 2008 at 02:53:27PM +0200, Martin Mares wrote:
> > Variable 'bgp_as4_support' decides whether this router support 4B ASN or
> > not. It is possible to disable 4B ASN support (using global option
> > 'disable_bgp_as4') (for example for testing or to workaround a bug in
> > the neighbor implementation of 4B ASN) but it shouldn't be neccessary to
> > change this setting. When bgs_as4_support is enabled, then native
> > representation of AS_PATH (type EAF_TYPE_AS_PATH) is 4 B per ASN,
> > otherwise it is 2 B per ASN.
> 
> I would really like to have this configurable per protocol instance
> -- when you want to work around a bug, you usually do not wish to
> disable the feature for the whole router, but only for the particular
> neighbor.

I will think about it.

> > The extended attribute AS4_PATH is used only when 4B-aware and
> > 4B-non-aware routers communicate together. If BIRD is 4B-aware,
> > then it discards such attribute ASAP, and when BIRD is not
> > 4B-aware, it is opaque attribute for it.
> 
> I have missed the fact that the attribute is only temporary at the
> first reading.
> 
> As a temporary attribute, it can well be opaque, but we should convert
> it to a common fixed format as soon as possible.

It is not converted - if BIRD is 4B-aware, then it is used (together
with 2B AS_PATH) to reconstruct real AS_PATH and then immediately
discarded. if BIRD is not 4B-aware, then BIRD should handle
it as unknown optional transitive atribute.

-- 
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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