Route table growth and hardware limits...talk to the filter

Fri Sep 21 18:22:04 UTC 2007

On Fri, 21 Sep 2007, John A. Kilpatrick wrote:
> 1.  The "captain obvious" suggestion of a default means that now I'm paying
> for multiple links but can only use one.  That's not cost effective and will
> provide lower performance for some destinations.  I have done defaults in
> the past where appropriate but it's not appropriate in this application.

That's not the case at all.  If you use only defaults, you could do 
load balancing but in a very crude fashion.  If you use a default 
route and filtered version of BGP feed (e.g., accept everything up to 
/21) probably up to 90-95% of traffic would go over that link, or 
multiple ones if you have multiple BGP sessions.

If you want more control than _only_ a default route or two (and many 
do), the default route would in principle be just a safeguard for more 
specifics (or other routes, based on a metric of your choosing) you 
filter out.

> 2.  The idea of a complex filtering strategy is, from my perspective, an
> even worse idea.  You get all of the downsides of a default with increased
> operational complexity that may not scale across multiple sites depending on
> the size of your ops team.

I'd probably agree if you used complex filtering without a default 
route.  Having a default route, as long as it points to a sufficiently 
good (non-tier1, not cogent) upstream allows you not to care so much 
about how you filter the BGP feed.

But as should be obvious, you don't need to worry about this problem 
if you're willing to put money into router upgrades.  However, I'm 
just suggesting there is an alternative to router upgrades if you're 
comfortable with the somewhat different tradeoffs that will bring with 
it.

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings