[c-nsp] Conditional advertise-map

[Gert Doering]

Hi,

On Wed, Sep 15, 2010 at 05:55:24PM +0100, Heath Jones wrote:
> You will probably find that the as path prepending will chew more memory
> than 1 more prefix matching an existing as path so the subnetting option
> works out better.

To the contrary.  Different AS paths are "just DRAM".  Every additional
prefix is "forwarding memory", read: limited and very expensive TCAM
(or SRAM or whatever).

[Lower-end routers have BGP tables and forwarding tables in the same
DRAM memory, so there it's "just DRAM", but for higher-end, the forwarding
tables go to hardware memory]

> just not cricket. I'm just trying to help him out with some suggestions. It
> would turn 1 prefix into 2 - thats hardly unreasonable..

Right now, about half(!) of the global routing table is deaggregates.

If those people would all aggregate properly, the routing table would
still fit into non-XL TCAMs - for us alone (and we're a small ISP) that
would have saved about 150.000 US$ in not-yet-needed TCAM upgrades.

It *does* matter.

gert
-- 
USENET is *not* the non-clickable part of WWW!
                                                           //www.muc.de/~gert/
Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de
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