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Présentation : As of 12.0, Cisco IOS routers include a little-known feature to aid in tracking changes to the routing table ip route profile. Here we examine how this feature offers an indicator of the network's stability. topology.png The routing table of any router in the above topology is predictable R1 show ip route Codes C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, - candidate default, U - per-user static route o - ODR, P - periodic downloaded static route Gateway of last resort is not set 10.0.0.0 24 is subnetted, 6 subnets C 10.0.10.0 is directly connected, Loopback0 C 10.0.12.0 is directly connected, FastEthernet0 0 C 10.0.13.0 is directly connected, FastEthernet0 1 O 10.0.30.0 110 11 via 10.0.13.3, 00 00 03, FastEthernet0 1 O 10.0.23.0 110 20 via 10.0.13.3, 00 00 03, FastEthernet0 1 110 20 via 10.0.12.2, 00 00 03, FastEthernet0 0 O IA 10.0.20.0 110 11 via 10.0.12.2, 00 00 03, FastEthernet0 0 First we need to enable route profiling R1 show ip route profile IP routing profile not enabled R1 conf t Enter configuration commands, one per line. End with CNTL Z. R1 config ip route profile R1 config Z R1 show ip route profile IP routing table change statistics Frequency of changes in a 5 second sampling interval ------------------------------------------------------------- Change Fwd-path Prefix Nexthop Pathcount Prefix interval change add change change refresh ------------------------------------------------------------- 0 0 0 0 0 0 1 0 0 0 0 0 2 0 0 0 0 0 3 0 0 0 0 0 4 0 0 0 0 0 5 0 0 0 0 0 10 0 0 0 0 0 15 0 0 0 0 0 20 0 0 0 0 0 25 0 0 0 0 0 30 0 0 0 0 0 55 0 0 0 0 0 80 0 0 0 0 0 105 0 0 0 0 0 130 0 0 0 0 0 155 0 0 0 0 0 280 0 0 0 0 0 405 0 0 0 0 0 530 0 0 0 0 0 655 0 0 0 0 0 780 0 0 0 0 0 1405 0 0 0 0 0 2030 0 0 0 0 0 2655 0 0 0 0 0 3280 0 0 0 0 0 3905 0 0 0 0 0 7030 0 0 0 0 0 10155 0 0 0 0 0 13280 0 0 0 0 0 Overflow 0 0 0 0 0 Route profiling works by inspecting the routing table every five seconds. Changes to routes between inspections are categorized into one or more of the five rightmost columns and their frequency is noted by row according to the leftmost column. For example, a value of 3 in the 2 row of the prefix refresh means that there were three five-second intervals during which two prefix refreshes occurred. Yes, it's a bit confusing. Before we dig any further, a description of each of the event columns as described in the documentation may be helpful Forward-Path Change - This statistic is the number of changes in the forwarding path, which is the accumulation of prefix-add, next-hop change, and pathcount change statistics. Prefix-Add - A new prefix was added to the routing table. Next-Hop Change - A prefix is not added or removed, but the next hop changes. This statistic is only seen with recursive routes that are installed in the routing table. Pathcount Change - The number of paths in the routing table has changed. This statistic is the result of an increase in the number of paths for an Interior Gateway Protocol IGP prefix in the routing table. Prefix Refresh - Standard routing table maintenance the forwarding behavior is not changed. Of course, the table is empty immediately after enabling route profiling. After a few minutes, however, we begin to notice significant values R1 show ip route profile IP routing table change statistics Frequency of changes in a 5 second sampling interval ------------------------------------------------------------- Change Fwd-path Prefix Nexthop Pathcount Prefix interval change add change change refresh ------------------------------------------------------------- 0 96 96 96 96 96 1 0 0 0 0 0 2 0 0 0 0 0 3 0 0 0 0 0 4 0 0 0 0 0 5 0 0 0 0 0 10 0 0 0 0 0 15 0 0 0 0 0 20 0 0 0 0 0 25 0 0 0 0 0 30 0 0 0 0 0 55 0 0 0 0 0 80 0 0 0 0 0 105 0 0 0 0 0 130 0 0 0 0 0 155 0 0 0 0 0 280 0 0 0 0 0 405 0 0 0 0 0 530 0 0 0 0 0 655 0 0 0 0 0 780 0 0 0 0 0 1405 0 0 0 0 0 2030 0 0 0 0 0 2655 0 0 0 0 0 3280 0 0 0 0 0 3905 0 0 0 0 0 7030 0 0 0 0 0 10155 0 0 0 0 0 13280 0 0 0 0 0 Overflow 0 0 0 0 0 We can see that all five events have a value of 96 in the 0 row. This tells us two things first, route profiling has been enabled for the last 8 minutes 96 5 seconds per interval 480 seconds 60 8 minutes . Second, since all columns only have an entry in the 0 row, this tells us that no changes have occurred in other words, the routing table has remained stable. But stability is boring, so let's force a change. Assume R2 loses its connection to the 10.0.23.0 30 network. This will be reflected as a change in the next update of the profile R1 show ip route profile IP routing table change statistics Frequency of changes in a 5 second sampling interval ------------------------------------------------------------- Change Fwd-path Prefix Nexthop Pathcount Prefix interval change add change change refresh ------------------------------------------------------------- 0 172 172 173 173 173 1 1 1 0 0 0 2 0 0 0 0 0 3 0 0 0 0 0 4 0 0 0 0 0 5 0 0 0 0 0 10 0 0 0 0 0 15 0 0 0 0 0 20 0 0 0 0 0 25 0 0 0 0 0 30 0 0 0 0 0 55 0 0 0 0 0 80 0 0 0 0 0 105 0 0 0 0 0 130 0 0 0 0 0 155 0 0 0 0 0 280 0 0 0 0 0 405 0 0 0 0 0 530 0 0 0 0 0 655 0 0 0 0 0 780 0 0 0 0 0 1405 0 0 0 0 0 2030 0 0 0 0 0 2655 0 0 0 0 0 3280 0 0 0 0 0 3905 0 0 0 0 0 7030 0 0 0 0 0 10155 0 0 0 0 0 13280 0 0 0 0 0 Overflow 0 0 0 0 0 At this point, there have been 172 intervals where no forward-path changes have occurred, 1 interval where a single forward-path change has occurred, and 0 intervals where any other number of forward-path changes have occurred. The same is true for prefix additions. The other three event categories remain unaffected all 173 intervals detected 0 changes applicable to those categories . If two such events were detected within the interval, 1 would appear in the 2 row of both columns instead. Likewise, if ten such events were detected within the interval, the 10 row would be incremented instead. When R2's link is restored, we see the second event reflected in the profile R1 show ip route profile IP routing table change statistics Frequency of changes in a 5 second sampling interval ------------------------------------------------------------- Change Fwd-path Prefix Nexthop Pathcount Prefix interval change add change change refresh ------------------------------------------------------------- 0 238 239 240 239 239 1 2 1 0 1 1 2 0 0 0 0 0 3 0 0 0 0 0 4 0 0 0 0 0 5 0 0 0 0 0 10 0 0 0 0 0 15 0 0 0 0 0 20 0 0 0 0 0 25 0 0 0 0 0 30 0 0 0 0 0 55 0 0 0 0 0 80 0 0 0 0 0 105 0 0 0 0 0 130 0 0 0 0 0 155 0 0 0 0 0 280 0 0 0 0 0 405 0 0 0 0 0 530 0 0 0 0 0 655 0 0 0 0 0 780 0 0 0 0 0 1405 0 0 0 0 0 2030 0 0 0 0 0 2655 0 0 0 0 0 3280 0 0 0 0 0 3905 0 0 0 0 0 7030 0 0 0 0 0 10155 0 0 0 0 0 13280 0 0 0 0 0 Overflow 0 0 0 0 0 By now you've no doubt deduced that lower values except the 0 row indicate a more-stable routing table. This feature probably isn't ideal for enterprise-wide network management, but might come in handy when attempting to detect sporadic and or short-lived fluctuations in the topology during troubleshooting.
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