[afnog] BGP Redondancy Test

[Mark Tinka]

On Thursday, October 14, 2010 04:25:28 am Regardt van de 
Vyver wrote:

> While some would strangle me for recommending this...

Yes, some of us would :-)...

> the
> following works reasonably well:
> Lets say you have a /21 of total space
> Announce the full /21 out to both ISPs
> Announce a set of /24's out each of the ISPs to balance
> inbound traffic
> 
> If either link fails the generic /21 will keep traffic
> flowing.

De-aggregation really isn't such a good idea. If the OP 
really has to de-aggregate in order to traffic engineer, let 
him, at the very worst, split the /21 into 2x /20's. /24's 
are eating up half of the DFZ's routing and forwarding 
tables. Adding more won't help the situation.

But before splitting up the allocation, let the OP toy with 
prepending, and also find out whether his upstreams supports 
BGP communities that can help influence how traffic returns 
to his network on at least one of the links.

Avoid de-aggregating as much as possible. Avoid de-
aggregating to multiple /24's, "EVER", when possible.

Cheers,

Mark.
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