An interesting problem came up that I thought I'd share and see if anyone has some thoughts. A user on one of our private networks was able to route fine to anything on his subnet but as soon as he attempted any routing to another subnet, the connection slowed to a crawl. We found that moving him from his IP (172.30.50.131) to another IP worked so upon further investigation I ran the following command and received this output:
#show ip cache IP routing cache 2 entries, 420 bytes 3996 adds, 3994 invalidates, 0 refcounts Minimum invalidation interval 2 seconds, maximum interval 5 seconds, quiet interval 3 seconds, threshold 0 requests Invalidation rate 0 in last second, 0 in last 3 seconds Last full cache invalidation occurred 00:03:09 ago Prefix/Length Age Interface Next Hop 172.30.50.131/32 00:02:54 Fa2/1.1 172.30.50.131 172.30.50.155/32 00:01:01 Fa2/1.1 172.30.50.155 Out of curiosity I changed the IP on a computer in the subnet to 172.30.50.155 and it had problems routing. I changed it to 172.30.50.131 and received the same routing problem. The problem cleared when I disabled route-caching on the FA2/1.1 interface servicing the 172.30.50.x subnet. The strange thing is there are a bunch of other very active IPs on this subnet and none of them show up in this list, only these two IPs. Route-caching is also enabled for other interfaces on this router but there are no entries for IPs behind those interfaces. I tried clearing the cache but it did not have an effect. Before: interface FastEthernet2/1 description [Office LAN] Connected to 3COM-3 Port 13 no ip address ip flow ingress ip route-cache policy ip route-cache flow no ip mroute-cache duplex full ipv6 enable ipv6 nd ra-interval 30 ipv6 nd prefix default 172800 172800 hold-queue 1500 in interface FastEthernet2/1.1 encapsulation dot1Q 1 native ip address 172.30.50.1 255.255.255.0 ip flow ingress no ip mroute-cache no snmp trap link-status ipv6 enable ipv6 nd ra-interval 30 ipv6 nd prefix default 172800 172800 After: interface FastEthernet2/1 description [Office LAN] Connected to 3COM-3 Port 13 no ip address ip flow ingress no ip route-cache cef no ip route-cache no ip mroute-cache duplex full ipv6 enable ipv6 nd ra-interval 30 ipv6 nd prefix default 172800 172800 hold-queue 1500 in interface FastEthernet2/1.1 encapsulation dot1Q 1 native ip address 172.30.50.1 255.255.255.0 ip flow ingress no ip route-cache no ip mroute-cache no snmp trap link-status ipv6 enable ipv6 nd ra-interval 30 ipv6 nd prefix default 172800 172800 This network has been up for years with this configuration and I've never seen this before. Another strange thing...since I changed the configuration, the output of show ip cache has expanded. Before, there were only the two 172.30.50.x entries. Now it looks like this: #show ip cache IP routing cache 137 entries, 25160 bytes 4212 adds, 4075 invalidates, 0 refcounts Minimum invalidation interval 2 seconds, maximum interval 5 seconds, quiet interval 3 seconds, threshold 0 requests Invalidation rate 0 in last second, 0 in last 3 seconds Last full cache invalidation occurred 00:20:27 ago Prefix/Length Age Interface Next Hop 8.0.0.0/8 00:05:21 FastEthernet1/0 10.1.1.1 12.0.0.0/8 00:13:28 FastEthernet1/0 10.1.1.1 17.0.0.0/8 00:09:01 FastEthernet1/0 10.1.1.1 24.0.0.0/8 00:13:22 FastEthernet1/0 10.1.1.1 32.0.0.0/8 00:05:49 FastEthernet1/0 10.1.1.1 38.0.0.0/8 00:13:16 FastEthernet1/0 10.1.1.1 63.0.0.0/8 00:13:01 FastEthernet1/0 10.1.1.1 64.0.0.0/8 00:13:31 FastEthernet1/0 10.1.1.1 65.0.0.0/8 00:13:31 FastEthernet1/0 10.1.1.1 66.0.0.0/8 00:12:24 FastEthernet1/0 10.1.1.1 xxx.xxx.xxx.131/32 00:07:43 FastEthernet2/0 xxx.xxx.xxx.131 xxx.xxx.xxx.132/32 00:09:11 FastEthernet2/0 xxx.xxx.xxx.132 xxx.xxx.xxx.141/32 00:13:31 FastEthernet2/0 xxx.xxx.xxx.141 xxx.xxx.xxx.143/32 00:07:20 FastEthernet2/0 xxx.xxx.xxx.143 xxx.xxx.xxx.148/32 00:04:23 FastEthernet2/0 xxx.xxx.xxx.148 xxx.xxx.xxx.161/32 00:00:48 FastEthernet2/0 xxx.xxx.xxx.161 xxx.xxx.xxx.162/32 00:13:05 FastEthernet2/0 xxx.xxx.xxx.162 xxx.xxx.xxx.169/32 00:01:55 FastEthernet2/0 xxx.xxx.xxx.169 xxx.xxx.xxx.170/32 00:00:11 FastEthernet2/0 xxx.xxx.xxx.170 xxx.xxx.xxx.175/32 00:13:27 FastEthernet2/0 xxx.xxx.xxx.175 xxx.xxx.xxx.178/32 00:13:17 FastEthernet2/0 xxx.xxx.xxx.178 xxx.xxx.xxx.179/32 00:05:38 FastEthernet2/0 xxx.xxx.xxx.179 xxx.xxx.xxx.181/32 00:13:31 FastEthernet2/0 xxx.xxx.xxx.181 xxx.xxx.xxx.186/32 00:13:31 FastEthernet2/0 xxx.xxx.xxx.186 xxx.xxx.xxx.188/32 00:13:19 FastEthernet2/0 xxx.xxx.xxx.188 67.149.83.0/26 00:13:16 FastEthernet1/0 10.1.1.1 67.163.65.0/26 00:05:13 FastEthernet1/0 10.1.1.1 67.192.167.0/26 00:00:35 FastEthernet1/0 10.1.1.1 67.195.133.0/26 00:02:09 FastEthernet1/0 10.1.1.1 67.207.146.128/26 00:02:06 FastEthernet1/0 10.1.1.1 67.207.147.128/26 00:02:06 FastEthernet1/0 10.1.1.1 67.207.149.0/26 00:01:55 FastEthernet1/0 10.1.1.1 67.207.149.128/26 00:02:06 FastEthernet1/0 10.1.1.1 67.223.66.64/26 00:12:16 FastEthernet1/0 10.1.1.1 67.223.78.128/26 00:09:04 FastEthernet1/0 10.1.1.1 67.223.238.0/26 00:13:31 FastEthernet1/0 10.1.1.1 67.228.101.128/26 00:10:54 FastEthernet1/0 10.1.1.1 67.228.212.192/26 00:05:22 FastEthernet1/0 10.1.1.1 68.0.0.0/8 00:00:11 FastEthernet1/0 10.1.1.1 69.0.0.0/8 00:01:21 FastEthernet1/0 10.1.1.1 70.0.0.0/8 00:03:24 FastEthernet1/0 10.1.1.1 72.0.0.0/8 00:13:19 FastEthernet1/0 10.1.1.1 74.0.0.0/8 00:03:25 FastEthernet1/0 10.1.1.1 75.0.0.0/8 00:01:52 FastEthernet1/0 10.1.1.1 76.0.0.0/8 00:09:07 FastEthernet1/0 10.1.1.1 77.0.0.0/8 00:09:58 FastEthernet1/0 10.1.1.1 82.0.0.0/8 00:12:25 FastEthernet1/0 10.1.1.1 87.0.0.0/8 00:12:25 FastEthernet1/0 10.1.1.1 91.0.0.0/8 00:13:18 FastEthernet1/0 10.1.1.1 94.0.0.0/8 00:12:47 FastEthernet1/0 10.1.1.1 98.0.0.0/8 00:13:29 FastEthernet1/0 10.1.1.1 128.121.0.0/16 00:13:28 FastEthernet1/0 10.1.1.1 149.20.0.0/16 00:13:13 FastEthernet1/0 10.1.1.1 164.55.0.0/16 00:12:08 FastEthernet1/0 10.1.1.1 166.205.0.0/16 00:10:15 FastEthernet1/0 10.1.1.1 168.143.0.0/16 00:13:29 FastEthernet1/0 10.1.1.1 172.30.100.0/24 00:13:30 FastEthernet2/0 xxx.xxx.xxx.184 174.37.0.0/16 00:09:56 FastEthernet1/0 10.1.1.1 Prefix/Length Age Interface Next Hop 174.145.0.0/16 00:10:03 FastEthernet1/0 10.1.1.1 192.5.6.0/24 00:02:29 FastEthernet1/0 10.1.1.1 192.12.94.0/24 00:01:43 FastEthernet1/0 10.1.1.1 192.31.80.0/24 00:09:42 FastEthernet1/0 10.1.1.1 192.48.79.0/24 00:03:15 FastEthernet1/0 10.1.1.1 192.52.178.0/24 00:02:52 FastEthernet1/0 10.1.1.1 192.168.60.2/32 00:13:26 FastEthernet0/0 192.168.60.2 192.168.60.3/32 00:13:19 FastEthernet0/0 192.168.60.3 192.168.60.17/32 00:13:19 FastEthernet0/0 192.168.60.17 192.168.60.18/32 00:13:21 FastEthernet0/0 192.168.60.18 192.168.60.20/32 00:12:53 FastEthernet0/0 192.168.60.20 192.168.60.21/32 00:13:09 FastEthernet0/0 192.168.60.21 192.168.60.30/32 00:11:03 FastEthernet0/0 192.168.60.30 192.168.60.31/32 00:09:22 FastEthernet0/0 192.168.60.31 192.168.60.80/32 00:13:11 FastEthernet0/0 192.168.60.80 192.168.60.85/32 00:10:10 FastEthernet0/0 192.168.60.85 192.168.60.88/32 00:13:14 FastEthernet0/0 192.168.60.88 192.168.60.89/32 00:13:17 FastEthernet0/0 192.168.60.89 192.168.60.90/32 00:13:17 FastEthernet0/0 192.168.60.90 192.168.60.91/32 00:00:08 FastEthernet0/0 192.168.60.91 192.168.60.93/32 00:02:23 FastEthernet0/0 192.168.60.93 192.168.60.94/32 00:13:23 FastEthernet0/0 192.168.60.94 192.168.60.96/32 00:06:36 FastEthernet0/0 192.168.60.96 192.168.60.97/32 00:04:14 FastEthernet0/0 192.168.60.97 192.168.60.98/32 00:05:17 FastEthernet0/0 192.168.60.98 192.168.60.100/32 00:09:31 FastEthernet0/0 192.168.60.100 192.168.60.105/32 00:02:31 FastEthernet0/0 192.168.60.105 192.168.60.107/32 00:13:15 FastEthernet0/0 192.168.60.107 192.168.60.115/32 00:13:30 FastEthernet0/0 192.168.60.115 192.168.60.116/32 00:13:35 FastEthernet0/0 192.168.60.116 192.168.60.120/32 00:13:30 FastEthernet0/0 192.168.60.120 192.168.60.121/32 00:13:21 FastEthernet0/0 192.168.60.121 192.168.60.229/32 00:13:14 FastEthernet0/0 192.168.60.229 192.168.60.245/32 00:13:31 FastEthernet0/0 192.168.60.245 192.168.135.0/24 00:10:15 FastEthernet1/0 10.1.1.1 192.168.152.0/24 00:07:33 FastEthernet1/0 10.1.1.1 192.168.239.0/24 00:09:56 FastEthernet1/0 10.1.1.1 199.7.48.0/24 00:01:19 FastEthernet1/0 10.1.1.1 199.7.57.0/24 00:13:16 FastEthernet1/0 10.1.1.1 204.13.8.0/24 00:01:09 FastEthernet1/0 10.1.1.1 204.58.233.0/24 00:08:40 FastEthernet1/0 10.1.1.1 205.128.91.0/24 00:01:53 FastEthernet1/0 10.1.1.1 205.188.7.0/24 00:13:33 FastEthernet1/0 10.1.1.1 205.188.9.0/24 00:13:19 FastEthernet1/0 10.1.1.1 205.188.10.0/24 00:13:25 FastEthernet1/0 10.1.1.1 205.188.13.0/24 00:03:24 FastEthernet1/0 10.1.1.1 205.188.248.0/24 00:03:32 FastEthernet1/0 10.1.1.1 205.203.131.0/24 00:05:12 FastEthernet1/0 10.1.1.1 206.16.21.0/24 00:02:31 FastEthernet1/0 10.1.1.1 206.33.47.0/24 00:01:52 FastEthernet1/0 10.1.1.1 207.38.101.0/24 00:01:41 FastEthernet1/0 10.1.1.1 207.171.185.0/24 00:07:43 FastEthernet1/0 10.1.1.1 207.171.191.0/24 00:10:51 FastEthernet1/0 10.1.1.1 207.200.75.0/24 00:09:42 FastEthernet1/0 10.1.1.1 207.200.95.0/24 00:10:07 FastEthernet1/0 10.1.1.1 208.46.163.0/24 00:13:09 FastEthernet1/0 10.1.1.1 208.66.65.0/24 00:02:03 FastEthernet1/0 10.1.1.1 208.68.57.0/24 00:12:23 FastEthernet1/0 10.1.1.1 208.80.152.0/24 00:12:09 FastEthernet1/0 10.1.1.1 208.85.40.0/24 00:13:09 FastEthernet1/0 10.1.1.1 208.85.41.0/24 00:13:09 FastEthernet1/0 10.1.1.1 208.85.44.0/24 00:09:30 FastEthernet1/0 10.1.1.1 208.111.144.0/24 00:09:34 FastEthernet1/0 10.1.1.1 208.184.36.0/24 00:10:59 FastEthernet1/0 10.1.1.1 209.97.50.0/24 00:08:26 FastEthernet1/0 10.1.1.1 209.131.36.0/24 00:12:48 FastEthernet1/0 10.1.1.1 Prefix/Length Age Interface Next Hop 209.135.129.0/24 00:13:36 FastEthernet1/0 10.1.1.1 209.170.97.0/24 00:04:06 FastEthernet1/0 10.1.1.1 216.34.207.0/24 00:00:22 FastEthernet1/0 10.1.1.1 216.38.164.0/24 00:05:29 FastEthernet1/0 10.1.1.1 216.38.169.0/24 00:01:42 FastEthernet1/0 10.1.1.1 216.108.240.0/24 00:04:55 FastEthernet1/0 10.1.1.1 216.137.45.0/24 00:02:24 FastEthernet1/0 10.1.1.1 216.178.33.0/24 00:02:32 FastEthernet1/0 10.1.1.1 216.223.0.0/24 00:09:30 FastEthernet1/0 10.1.1.1 216.252.108.0/24 00:07:18 FastEthernet1/0 10.1.1.1 216.252.120.0/24 00:04:44 FastEthernet1/0 10.1.1.1 216.252.121.0/24 00:13:22 FastEthernet1/0 10.1.1.1 216.252.124.0/24 00:00:23 FastEthernet1/0 10.1.1.1 Why can't 172.30.50.131 and .155 IPs route outside the subnet when route-caching is enabled on the interface yet all the other IPs on the same subnet can? Why did all the other IPs pop up in the show ip cache output after removing route-caching from the FA2/1.1 172.30.50.x interface? Any help/thoughts would be appreciated, thanks. Spencer _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
