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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Routing vs Switching (was Re: Another UUNET Explanation)
"Chris A. Icide" <[email protected]> writes: smd> A clumsy tech or a backhoe takes out a physical path smd> between two POPs, each of which contains several routers smd> that form part of this flat network. smd> What happens now? > Layer 2 heals itself, without the knowledge of layer 3. Layer 3 > experiences a latency increase between certain paths. > > Sorry, had to do it. > > *duck* Well, this is certainly the obvious approach, and is certainly in line with the generally reasonable philosophy of "degraded performance rather than no performance" response to partitions, assuming the routers don't notice a topology change. There are some interesting issues with respect to convergence at the L2 layer (rerouting VCs takes time too), and I've seen problems where the fast-packet layer converged slowly enough that IS-IS adjacencies were lost, causing really neat routing slosh as the VC went and came back. (To augment one of my own questions, when you have two routers in a full mesh (FR, ATM, whatever using VCs) and the VC between N-1 and N-2 goes out of service, how do N-1 and N-2 decide what path(s) to use to talk to each other? Feel free to consider a network using any commonly available IGP and the iBGP hack.) I also have some anecdotes about VCs improperly travelling along the same path for long periods of time because of configuration errors or unnoticed physical disconnectivities between switches. There have also been neat tales of VCs going simplex from time to time. Monitoring two networks simultaneously, fun fun fun... :) I'm sure there are people here with practical experiences who might be willing to share what they've learned. > however, in this fast paced industry, will we > ever have the "perfect" protocol (okay, ever is a big > word). IPv6 over ATM/LANE with RSVP will someday change the world. Sean. - -- Sean Doran <[email protected]> "Boy, you obviously don't have a clue!" -- Chad Skidmore, Data Source L.L.C.
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