disconnected autonomous systems

Wed Nov 13 20:28:07 UTC 2002

There is a significant difference between not aggregating, and using
discontiguous-AS EBGP.

As long as you are familiar with the pitfalls, there is nothing
inherently wrong with using a single AS in multiple locations, and
advertising discrete blocks of address space in each one. The best reason
to do this is for a network that you eventually plan to merge - it
eliminates issues of having to make major BGP configuration changes.

Of course, it required you to point default routes out your upstreams, as
you will not see the prefixes from one discontiguous island, in another,
thanks to BGP loop detection.

Several large access ISPs have run in the fashion for extended periods.

As far as aggregation - they are a couple reasons to not aggregate, but
the vast majority of it is sloth.

Finally, in regard to "vocal opinions on NANOG" - well, anyone who has
read NANOG for a while knows that vocal isn't always correct.

- Daniel Golding

On Wed, 13 Nov 2002, Ralph Doncaster wrote:

>
> I've found there are many providers that have completely disconnected
> autonomous systems.  For example Yipes (6517) uses L3 on the west coast
> and Williams on the east coast.
> 66.7.129.0/24 is advertised under their AS through WCG and
> 209.213.209.0/24 is advertised under their AS through L3.
>
> And the number of connected autonomous systems with de-aggregated
> prefixes appears to be even more common than a disconnected AS.
>
> It would seem that many (most?) network operators are just ignoring the
> more vocal opinions on NANOG.
>
> -Ralph
>
>
>