[c-nsp] IP Route Cache - Unable to Route
Spencer Barnes
spencer at ceiva.com
Fri Oct 23 17:27:19 EDT 2009
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
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