[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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