Debug IP Routing Command on CISCO Router/Switch


Debug IP Routing


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.


Router#debug ip routing


In the below example we enable debug ip routing.

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

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

R3(config)#do sh run | sec ospf
router ospf 1
network 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

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

*Mar 1 01:19:06.195: RT: SET_LAST_RDB for
NEW rdb: via

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

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.
*Mar 1 01:19:28.891: RT: del via, ospf metric [110/2]
*Mar 1 01:19:28.895: RT: delete subnet route to
*Mar 1 01:19:28.899: RT: NET-RED
*Mar 1 01:19:28.903: RT: delete network route to
*Mar 1 01:19:28.903: RT: NET-RED

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