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Re: Route table growth and hardware limits...talk to the filter
- From: Warren Kumari
- Date: Fri Sep 21 15:44:36 2007
On Sep 21, 2007, at 2:22 PM, Pekka Savola wrote:
On Fri, 21 Sep 2007, John A. Kilpatrick wrote:
1. The "captain obvious" suggestion of a default means that now
for multiple links but can only use one. That's not cost
effective and will
provide lower performance for some destinations. I have done
the past where appropriate but it's not appropriate in this
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.
Sure, but you do still run the (not insignificant) risk of following
the default to the "sufficiently good (non-tier1, not cogent)
upstream", only to discover that, for whatever reason, it has no
reachability to the prefix. If I have spent to time and effort to get
multiple providers, presumably I believe that my bits are important
enough to not trust to "this will probably work most of the time..."
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
even worse idea. You get all of the downsides of a default with
operational complexity that may not scale across multiple sites
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
Hope is not a strategy.
-- Ben Treynor, Google