[10528] in North American Network Operators' Group
Re: Aggressive route flap dampening
daemon@ATHENA.MIT.EDU (Tony Li)
Tue Jul 8 02:02:07 1997
To: smd@clock.org (Sean M. Doran)
cc: nanog@merit.edu
From: Tony Li <tli@jnx.com>
Date: 07 Jul 1997 22:57:37 -0700
In-Reply-To: smd@clock.org's message of 7 Jul 97 20:44:28 GMT
smd@clock.org (Sean M. Doran) writes:
> The "N" should be reduced (or the time period lengthened) and the
> cost of increasing that ratio should increase with the length of
> the prefix, in order to encourage topologically sound aggregation
> either through traditional means or through NAT and NAT-like boxes
> such as the one described and implemented by Paul Vixie.
Here's where we part company. Varying the 'charge', either monetary or in
flap penalty creates an incorrect incentive: folks are incented to use a
shorter prefix. Note that this is distinct from aggregation in that they
may simply use a shorter prefix and not actually use more address space,
thus hurting netwide utilization.
The 'correct' incentive is a charge for flapping and a charge for
announcement. Both have real costs, directly traceable to processor and
memory costs.
> It fixed two problems simultaneously: firstly, there is lots of flap
> and flap is most irritating when relatively unimportant (and statistically
> small is likely to be less important than large) NLRI is responsible for
> a disproportionally large amount of it. Secondly, there are lots of
> networks which really ought to be aggregated. When a single up/down or
> up/down/up flap makes the network unusable for an hour or two, people
> generally become motivated either to be very very stable or to aggregate
> even adjacent aggregatable /24s in order to suffer fewer disconnectivities.
Note that both of these are 'fixed' without a length restriction: the per
prefix charge incents folks to aggregate. The per flap charge incents them
to stability. Direct cause and effect, without harmful side effects. ;-)
Tony
