Re: Various DECnet MIB questions & Adjacency index
EMA - we manage almost anything! <sylor@blumon.enet.dec.com> Fri, 28 August 1992 19:40 UTC
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Date: Fri, 28 Aug 1992 12:33:42 -0700
From: EMA - we manage almost anything! <sylor@blumon.enet.dec.com>
To: phiv-mib@pa.dec.com
Cc: sylor@blumon.enet.dec.com
Apparently-To: phiv-mib@Pa.dec.com
Subject: Re: Various DECnet MIB questions & Adjacency index
> I'd at least ask that we generate and document a rule as to which route is > returned, if there are multiple possibilities. How about lowest circuit > index first, followed by lowest next-hop address for multiple choices on > the same circuit. > > Art Art brings up a good point. In a multiple path network, you'ld like some consistency in which path is shown. The "first circuit", and then the "lowest number" adjacency are good choices. But that reminds me of a bit of folklore that you might want to know. It is important that the "first circuit" be deterministic. As long as the router's configuration doesn't change, the indexes of the circuits should be the same. And it would be good if the order of the circuits by index was the same as the alphabetic order of the circuits by name. There is a requirement that table indices be stable and deterministic in one of the SNMP specs, I forget which. But the determinism I'm looking for is not just a requirement for network management, it is also a requirement for correct operation of routing. We ran into a problem years ago when an implementation of DECnet indexed the circuits based on the order they came up. Well, given phases of the moon and other variables, the circuits ended up having a different order each time the router booted. That changed the whole routing pattern in the network (this was before path splitting) since if a router had 2 paths of equal cost, on Monday all packets would go left, and Tuesday all packets would go right, even though the network global configuration was exactly the same. Gave us no end of trouble in trying to come up with a workable network design or in diagnosing problems with "flaky routers". Because of that experience, we became pretty fanatical about making routing deterministic. The most visible example of this is the "tie breaking" algorithm in chosing a dedicated router based on highest ID. Well, there's some free advice. Mark
- Re: Various DECnet MIB questions & Adjacency index EMA - we manage almost anything!
- Re: Various DECnet MIB questions & Adjacency index EMA - we manage almost anything!