Debug IP Routing Command on CISCO Router/Switch

Command

Debug IP Routing

Use

This command enables debugging messages related to the routing table. This debug is particularly useful for finding routing loops. Since the routing table is normally stable, you will only see debug messges when there are route changes.

Syntax

Router#debug ip routing

Example

In the below example we enable debug ip routing.

R2(config)#do debug ip routing
IP routing debugging is on
R2(config)#

Now on R3, will we add a new interface under the OSPF process

R3(config)#do sh run | sec ospf
router ospf 1
log-adjacency-changes
network 0.0.0.0 255.255.255.255 area 0

R3(config)#int lo44
*Mar 1 19:45:07.287: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback44, changed state to up
R3(config-if)#ip add 44.44.44.44 255.255.255.255

On R2 we can see the debug output for R2 adding the new OSPF route.

R2(config)#
*Mar 1 01:19:06.195: RT: SET_LAST_RDB for 44.44.44.44/32
NEW rdb: via 10.2.2.3

*Mar 1 01:19:06.199: RT: add 44.44.44.44/32 via 10.2.2.3, ospf metric [110/2]
*Mar 1 01:19:06.203: RT: NET-RED 44.44.44.44/32

Now on R3 we will remove the interface we added from the OSPF process.

R3(config-if)#no int lo44
On R2 we can see the debug output for R2 displaying the status messages related to deleting the new OSPF route.
R2(config)#
*Mar 1 01:19:28.891: RT: del 44.44.44.44/32 via 10.2.2.3, ospf metric [110/2]
*Mar 1 01:19:28.895: RT: delete subnet route to 44.44.44.44/32
*Mar 1 01:19:28.899: RT: NET-RED 44.44.44.44/32
*Mar 1 01:19:28.903: RT: delete network route to 44.0.0.0
*Mar 1 01:19:28.903: RT: NET-RED 44.0.0.0/8

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