Default root and show ip route x.x.x.x

Answered Question
Aug 9th, 2008
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Hi there,


Got this routing problem in my lab at home and looking for some advice.


I have 3 routers R1 > R2 > R3. R3 is the end router advertising a default root via RIP v2. All 3 routers are running classless routing.


All routing between subnets is working a treat. Below is an extract of the routing tables from each router.


R1

Gateway of last resort is 10.151.2.1 to network 0.0.0.0


10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks

R 10.149.3.0/24 [120/2] via 10.151.2.1, 00:00:21, Serial0/0

R 10.149.2.0/24 [120/2] via 10.151.2.1, 00:00:21, Serial0/0

R 10.150.2.0/30 [120/1] via 10.151.2.1, 00:00:21, Serial0/0

C 10.151.2.0/30 is directly connected, Serial0/0

C 192.168.1.0/24 is directly connected, FastEthernet0/0

R* 0.0.0.0/0 [120/2] via 10.151.2.1, 00:00:21, Serial0/0


R2


Router with up/up interface 10.151.2.1


Gateway of last resort is 10.150.2.2 to network 0.0.0.0


10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks

R 10.149.3.0/24 [120/1] via 10.150.2.2, 00:00:27, Serial0

R 10.149.2.0/24 [120/1] via 10.150.2.2, 00:00:27, Serial0

C 10.150.2.0/30 is directly connected, Serial0

C 10.151.2.0/30 is directly connected, Serial1

R 192.168.1.0/24 [120/1] via 10.151.2.2, 00:00:27, Serial1

R* 0.0.0.0/0 [120/1] via 10.150.2.2, 00:00:27, Serial0


R3


Router with up/up interface 10.150.2.2


Gateway of last resort is 0.0.0.0 to network 0.0.0.0


86.0.0.0/30 is subnetted, 1 subnets

C 86.54.12.56 is directly connected, Ethernet0

10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks

C 10.149.3.0/24 is directly connected, Loopback2

C 10.149.2.0/24 is directly connected, Loopback1

C 10.150.2.0/30 is directly connected, Serial0

R 10.151.2.0/30 [120/1] via 10.150.2.1, 00:00:07, Serial0

R 192.168.1.0/24 [120/2] via 10.150.2.1, 00:00:07, Serial0

S* 0.0.0.0/0 is directly connected, Ethernet0


If i run a 'show ip route 25.25.25.5 from any router i receive a message stating the network is not in the table, which i dont understand, i thought the default route takes care of this? depending on classful/classless routing.


Also, if i run a tracert www.cisco.com from a host off R1 i see routes the packet is taking. See below.


1 <1 ms <1 ms <1 ms 192.168.1.1

2 23 ms 23 ms 23 ms 10.151.2.1

3 47 ms 44 ms 44 ms 10.150.2.2


So how come, when using a show ip route from the IOS it returns - network not in table even though the packet is being routed?


Any advice would be great!


Cheers,

Garry

Correct Answer by Giuseppe Larosa about 8 years 7 months ago

Hello Garry,

what you see is normal: when you do sh ip route 25.25.25.5 the router will look to find a match in the ip routing table.

If there isn't a prefix in the routing table the answer is the one you see.

With a single notable execption: the net 0.0.0.0/0 is never considered a match for a prefix.

By the way, sh ip route 0.0.0.0 provides a result only when a default route is present in the routing table.

I usually do this way

sh ip route x.x.x.x

if the answer is not in table I check if there is a default with

sh ip route 0.0.0.0


Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Sat, 08/09/2008 - 12:55
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Hello Garry,

what you see is normal: when you do sh ip route 25.25.25.5 the router will look to find a match in the ip routing table.

If there isn't a prefix in the routing table the answer is the one you see.

With a single notable execption: the net 0.0.0.0/0 is never considered a match for a prefix.

By the way, sh ip route 0.0.0.0 provides a result only when a default route is present in the routing table.

I usually do this way

sh ip route x.x.x.x

if the answer is not in table I check if there is a default with

sh ip route 0.0.0.0


Hope to help

Giuseppe

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