pd table vs 6296

Fri Sep 22 16:41:10 UTC 2017

On 9/21/17 18:59, Randy Bush wrote:
> say i want to use pd to a fairly large aggregation.  the router has to
> hold the pd table.  it sees some routers have limited table size, e.g.
> 1k.  so what's a poor boy to do?  the classic ipv4 solution would be
> 6296 <the horror!>.  are folk doing pd scaling?  how?
>
> randy	  
>
This is kind of in the neighborhood of stupid pet tricks, but I've done
it to substantially increase the table size in a non-pd scenario, so
there is that.

In an accommodating switch, program a particular prefix length (say 56
or 48 ending on a byte offset) to be installed and matched in the exact
match table. Voila your PD routes are now host routes, and the table for
VLSM routes is free for other purposes.

1. Isn't this robbing peter to pay paul? - yes

2. Is this some kind of strange classful addressing hetrodoxy? - not
really, masks just happen to be expensive.

3. How does this work with variable length prefix delegation? - all PD
prefixes are the same (maximum) size and you install them in the routing
table accordingly> what the end system asks for and what they do with it
when you route it to them are both their business. A decent (not
necessarily high end) L3 switch will let you partition the CAM  in
several variations that are more or less appropriate for this application.

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