[c-nsp] Question about BGP MRAI on Cisco

[Tantsura, Jeff]

Hi ,

I know that Juniper doesn't do MRAI, so it sends all new updates immediately out.
Cisco, according to some doc's does 30 sec over EBGP and 5 sec over IBGP sessions.

The question:

Does MRAI work on first update or only on the next ones ?
In other words when a BGP router gets new update will it wait until MRAI timer expires (different for EBGP and IBGP)
or will it send this update (after it's placed in Adj-RIBs-Out) immediately out and apply MRAI timer to the next similar update.

Thanks in advance

>From RFC 1771:

9.2.3.1 Frequency of Route Advertisement

   The parameter MinRouteAdvertisementInterval determines the minimum
   amount of time that must elapse between advertisement of routes to a
   particular destination from a single BGP speaker. This rate limiting
   procedure applies on a per-destination basis, although the value of
   MinRouteAdvertisementInterval is set on a per BGP peer basis.

   Two UPDATE messages sent from a single BGP speaker that advertise
   feasible routes to some common set of destinations received from BGP
   speakers in neighboring autonomous systems must be separated by at
   least MinRouteAdvertisementInterval. Clearly, this can only be
   achieved precisely by keeping a separate timer for each common set of
   destinations. This would be unwarranted overhead. Any technique which
   ensures that the interval between two UPDATE messages sent from a
   single BGP speaker that advertise feasible routes to some common set
   of destinations received from BGP speakers in neighboring autonomous
   systems will be at least MinRouteAdvertisementInterval, and will also
   ensure a constant upper bound on the interval is acceptable.

   Since fast convergence is needed within an autonomous system, this
   procedure does not apply for routes receives from other BGP speakers
   in the same autonomous system. To avoid long-lived black holes, the
   procedure does not apply to the explicit withdrawal of unfeasible
   routes (that is, routes whose destinations (expressed as IP prefixes)
   are listed in the WITHDRAWN ROUTES field of an UPDATE message).

   This procedure does not limit the rate of route selection, but only
   the rate of route advertisement. If new routes are selected multiple
   times while awaiting the expiration of MinRouteAdvertisementInterval,
   the last route selected shall be advertised at the end of
   MinRouteAdvertisementInterval.

9.2.3.2 Frequency of Route Origination

   The parameter MinASOriginationInterval determines the minimum amount
   of time that must elapse between successive advertisements of UPDATE
   messages that report changes within the advertising BGP speaker's own
   autonomous systems.



With kind regards/ met vriendelijke groeten,
--------------------------------------------------------
Jeff Tantsura
CCIE #11416
Senior Consultant
Capgemini Nederland BV
Tel: +31(0)30 689 2866
Mob:+31(0)6 4588 6858
Fax: +31(0)30 689 6565
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