"2M today, 10M with no change in technology"? An informal survey.

Florian Weimer fw at deneb.enyo.de
Sun Aug 26 08:41:46 UTC 2007

* Deepak Jain:

> When it comes to an FIB, there are only say 100-200 destinations on a
> big router (outbound). Irrespective of the 2M or 20M routes it
> has. Even though the entire Internet isn't aggregated the way it
> should be, for FIB purposes, the router knows how it will route out to
> its 100-200 destinations (ports).

Could be more than that in some MPLS and IXP environments, but in
essence, that's true.

> Couldn't it just aggregate before it drops routes into its FIB and
> only import specifics (deagg) if a destination changes for a more
> specific prefix [like the swamp]? We talk about default-free zones as
> needing every prefix, and they do (for propagation purposes) but for
> FIB purposes, they really don't.

My understanding is that there are no known algorithms for fast
updates (and particularly withdrawals) on aggregated FIBs, especially
if those FIBs are stored in CIDR form.  This is the prime reason why
all those Cisco 65xx/76xx with MSFC2/PFC2 will be worthless junk in a
couple of months.

But I'm sure that this is not the end of the story.

> For example, a router with only 1 connection (no matter how many
> routes being sent by its upstream), would only have 1 route entered
> into its FIB -- because no matter where the route goes, it can go
> upstream.

This will cause routing loops for unallocated address space.

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