too many routes

Sean M. Doran smd at
Thu Sep 11 00:50:12 UTC 1997

Nathan Stratton <nathan at> writes:

> This is what I beleave sprint is doing. They are using the new Cisco 12000
> GSR with external router servers. It is a smart way of patching the
> problem. If you need more CPU or memory you can just add a bigger box and
> more RAM. 

The GSRs are to move bits fast.  They are not to act as
route servers.

Sprint recently announced that they are deploying 622Mbps
POS cross-country links, and the GSRs are the only things
you can put on the ends of such beasts that are available

(Someone may point out that it may not be the only choice
for very long, however, it's the only one whose design I
know and have had any influence upon, and is therefore
frankly the only one I trust, although I don't expect the
people building the competing box will ship anything but a
good product even if they are now rather deeply in bed
with the cell-heads and about as transparent to most
observers as the Kremlin during the cold war...  The
box being built by someone who actually worked very close
to the Kremlin during the cold war is also something I
don't know enough about, however that is much more due to my
neglect than due to organizational attitude.)

Remember that a current snapshot is not a good indicator
of future health.   Sure the processing demands of routing
are such that the GSR's main CPU is largely idle after
converging with its neighbours, however there is still a
CPU spike during convergence and the processing load is
non-zero.  If you increase the growth curve of the number
of prefixes, you increase the CPU demands during
large-scale convergence.  You also statistically increase the
CPU demand after convergence unless you reduce the
probability of any given prefix transitioning from up to
down or vice versa over time.

If you have a growth curve where the processing load
during large-scale convergence and the processing load to
handle background noise increases beyond processing
capacity faster than processing capacity can be increased,
you lose, no matter how crunchy your box is today relative
to today's processing demands.

In other words, removing the feedback mechanisms on the
growth of the number of globally-visible prefixes and on
prefix instability is probably a really bad idea.


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