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## Re: Comparison of symmetric and asymmetric PLSN algorithms

 Subject: Re: Comparison of symmetric and asymmetric PLSN algorithms Alia Atlas Tue, 14 Jun 2005 16:06:22 -0400
 ```Mike, At 01:33 PM 6/14/2005, mike shand wrote: ```I just tried a randomly generated topology with all (very) asymmetric links and managed to produce a 9 hop loop, which traversed 6 type C nodes, 2 type As and a type B!!! Excellent! I assume this was using the symmetric condition- because there are type As and a type B in it? Um... what am I missing here? It is still possible to get type A and B with the asymmetric condition isn't it? ``` What does it look like using the asymmetric one? ``````I get the loop with both sym and asym conditions. ```I'm a bit confused then. A multi-hop loop with the asymmetric condition shouldn't go through type A or type B nodes. That's the point of changing the condition to be stricter. ```Yes, but it can still be fed back into it by a chain of C's ```Thanks for the copious examples :-) I see exactly what you're talking about now. Essentially, the shortest path in one direction between 2 type Cs might be via multiple hops that are type C. I hadn't fully appreciated that. ```Alia ```So in the example I gave, for a destination of node 7 (which is at the other end of a link connected to node 22) we have nodes 3 & 19 which are type A even with the asym condition. After the failure 3's route to 7 is via 19 (and hence 19 is downstream), but before the failure 19 is also downstream, since 19's route to 7 is via nodes 2 and 26. hence 19 is a safe neighbor. Similarly, after the failure 19's route to 7 is via 8 (hence 8 is downstream). Before the failure 19's route is via 2 (as before), but 8 has a path via 26. hence it is downstream of 19 both before and after the failure. ```After the failure, 22's route to 7 is via 29,18,28,3,19,8,1,9,7. BTW if I didn't mention it before the failing link is between 22 and 7. If it helps, the following describes the topology Much of it is irrelevant, but it is just what got randomly created. link 2 to 12 cost 257 rev 4530 link 18 to 30 cost 265 rev 3480 link 19 to 2 cost 146 rev 30 link 22 to 7 cost 261 rev 2620 link 23 to 17 cost 368 rev 3830 link 24 to 17 cost 193 rev 2710 link 25 to 13 cost 142 rev 1720 link 26 to 11 cost 312 rev 1800 link 27 to 4 cost 356 rev 3450 link 28 to 10 cost 219 rev 4420 link 29 to 5 cost 246 rev 2450 link 1 to 9 cost 500 rev 2950 link 3 to 19 cost 408 rev 1200 link 6 to 14 cost 264 rev 320 link 8 to 26 cost 135 rev 4580 link 12 to 24 cost 126 rev 4100 link 15 to 6 cost 205 rev 3330 link 18 to 28 cost 402 rev 130 link 22 to 20 cost 189 rev 3920 link 23 to 24 cost 496 rev 2770 link 25 to 28 cost 116 rev 4890 link 27 to 21 cost 488 rev 3390 link 29 to 22 cost 430 rev 1100 link 1 to 8 cost 100 rev 630 link 2 to 26 cost 148 rev 3630 link 3 to 25 cost 227 rev 4550 link 4 to 16 cost 15 rev 4460 link 11 to 16 cost 319 rev 2650 link 12 to 26 cost 11 rev 2720 link 14 to 15 cost 139 rev 400 link 18 to 23 cost 64 rev 860 link 19 to 17 cost 357 rev 2030 link 27 to 30 cost 383 rev 4880 link 29 to 21 cost 156 rev 2400 link 1 to 15 cost 68 rev 4630 link 2 to 23 cost 157 rev 2610 link 3 to 28 cost 384 rev 790 link 4 to 24 cost 301 rev 770 link 5 to 20 cost 16 rev 4600 link 6 to 12 cost 413 rev 3990 link 7 to 9 cost 236 rev 2690 link 8 to 19 cost 301 rev 1200 link 10 to 30 cost 479 rev 950 link 11 to 22 cost 178 rev 2870 link 13 to 27 cost 440 rev 3360 link 14 to 25 cost 359 rev 3140 link 18 to 29 cost 241 rev 2310 ```Sorry its overly complex. I'm sure it would be possible to extract a subset which had the required properties. ``` Mike ```Regardless of whether a node is using the old topology or the new topology, with the asymmetric condition, a type A or a type B router will use a next-hop between DELAY_SPF and DELAY_TYPEB will be closer to the destination. This guarantees monotonically decreasing distance, so that loops cannot form. Thus, a multi-hop micro-loop could go through a lot of type C's, but as soon as it hits a type B or type A, I'd think it would exit the loop. Maybe I'm missing something. I guess it might be possible for a type C to send back up , but I'm not seeing how. Consider a type A node A and a type C node C - where C is the first type C node encountered on A's next-hop path to D (where this path is that used between DELAY_SPF and DELAY_TYPEB). ```We know that: D_old(A, D) > D_old(C,D) D_new(A, D) > D_new(C, D) ```Can you describe the topology you're using? I'm not picturing how one could get the multi-hop micro-loop between type A, B and C when using the asymmetric condition. Do you think we can adequately describe the topology conditions that can lead to the multi-hop micro-loop problem with the symmetric condition? ```Perhaps, but I'm not going to attmept it right now:-) ``````Not a 5-minute response-time email? I'm shocked :-) Alia `````` Mike ``````Alia ``````Testing path from node 8 (8) to node 7 (7) at time 1 Node 8 (8): Packet discarded because looped Node 19 (19) New: Forwarded via adj 1 over link 42 to node 8 Node 3 (3) New: Forwarded via adj 1 over link 13 to node 19 Node 28 (28) New: Forwarded via adj 1 over link 37 to node 3 Node 18 (18) New: Forwarded via adj 1 over link 18 to node 28 Node 29 (29) New: Forwarded via adj 1 over link 47 to node 18 Node 22 (22) New: Forwarded via adj 1 over link 23 to node 29 Node 11 (11) Temp: Forwarded via adj 1 over link 44 to node 22 Node 26 (26) Old: Forwarded via adj 1 over link 8 to node 11 Node 8 (8) Old: Forwarded via adj 1 over link 15 to node 26 (read the trace going up) Node 11 is type B and nodes 3 and 11 are type A for the destination node 7 ```So at time 1 (when the type C's change), type A MUST forward according to new topology, type B according to the temporary type B next hop, and the type C either according to old or new topology (since they are in the process of changing) ```So, yes, we can get multi-hop loops with the asymmetric algorithm! Mike `````` _______________________________________________ Rtgwg mailing list [email protected] https://www1.ietf.org/mailman/listinfo/rtgwg ```
 Current Thread Comparison of symmetric and asymmetric PLSN algorithms, mike shand Re: Comparison of symmetric and asymmetric PLSN algorithms, Alia Atlas Message not available Re: Comparison of symmetric and asymmetric PLSN algorithms, mike shand Re: Comparison of symmetric and asymmetric PLSN algorithms, Alex Zinin Re: Comparison of symmetric and asymmetric PLSN algorithms, Alia Atlas Re: Comparison of symmetric and asymmetric PLSN algorithms, mike shand Re: Comparison of symmetric and asymmetric PLSN algorithms, Alia Atlas Re: Comparison of symmetric and asymmetric PLSN algorithms, mike shand Re: Comparison of symmetric and asymmetric PLSN algorithms, Alia Atlas <=