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sunny.wongwc
Beginner

3750X routed to incorrect next hop IP

Hi Brothers and Sisters

I got a strangh routing problem on our 3750X which found that from the traceroute that some specific destination cannot route to the next hop IP configured in static route.

-----------------------------------------                                      -------------------------------------            ----------------------------------------

|   3750-Office (10.1.99.198) |      --(MetroE Circuit)----   | 3750-DC (10.1.99.199)  |  --------  | MPLS Router (10.1.1.30) |

------------------------------------------                                     --------------------------------------           ----------------------------------------

//Routing info of 192.168.100.240

C3750Xa-DataCenter#sh ip route 192.168.100.240

Routing entry for 192.168.96.0/21, supernet

  Known via "static", distance 1, metric 0

  Redistributing via rip

  Advertised by rip

  Routing Descriptor Blocks:

  * 10.1.1.30

      Route metric is 0, traffic share count is 1

//Routing info of 192.168.97.30 (This can route correctly)

C3750Xa-DataCenter#sh ip route 192.168.97.30 

Routing entry for 192.168.96.0/21, supernet

  Known via "static", distance 1, metric 0

  Redistributing via rip

  Advertised by rip

  Routing Descriptor Blocks:

  * 10.1.1.30

      Route metric is 0, traffic share count is 1

However when traceroute to 192.168.100.240 it was found that routed to different nexthop IP.

//Traceroute to 192.168.100.240 Incorrect next hop IP

C3750Xa-DataCenter#traceroute 192.168.100.240

Type escape sequence to abort.

Tracing the route to 192.168.100.240

  1 10.1.99.198 0 msec 8 msec 9 msec

  2 10.11.1.2 8 msec 8 msec 0 msec

  3 10.1.99.198 9 msec 0 msec 8 msec

  4 10.11.1.2 9 msec 8 msec 0 msec

//Traceroute to 192.168.97.30 (Correct next hop IP)

C3750Xa-DataCenter#traceroute 192.168.97.30 

Type escape sequence to abort.

Tracing the route to 192.168.97.30

  1 10.1.1.30 8 msec 0 msec 9 msec

  2 172.25.0.1 8 msec 8 msec 0 msec

  3 172.25.1.1 235 msec 235 msec 226 msec

4 172.25.1.2 235 msec *  235 msec

And CEF table shows everything normal and to correct next hop.

//CEF to 192.168.100.240

C3750Xa-DataCenter#sh ip cef 192.168.100.240 d

192.168.96.0/21, epoch 3

  recursive via 10.1.1.30

    attached to Vlan10

//CEF to 192.168.97.30

C3750Xa-DataCenter#sh ip cef 192.168.97.30 d 

192.168.96.0/21, epoch 3

  recursive via 10.1.1.30

    attached to Vlan10

Anyone whats the problem is? I guess there must be some problem in the FIB table, but I am not sure how to continue the troubleshooting.

Thx

Sunny Wong

3 REPLIES 3
paul driver
VIP Mentor

Hello

Looks like you have recursive routing,

Is the 3780switch is obtaining the static via redistributing static command without the ip route 0.0.0.0 0.0.0.XXXX From the DC router? Default-originate would be a better choice if applicable.

Is there a gateway of last resort set?
What version of rip is running and is auto summarisation turned off if ripv2 is in use

On the 3780:
Sh ip route rip

Res
Paul

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kind regards
Paul

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future
sunny.wongwc
Beginner

Hi Paul

Thanks for your reply. Am...you can saw from the "show ip route xxxx" output, it is a static route configured on the 3750 manually not by learning from RIP.

And both 192.168.100.240 and 192.168.97.xx are under the same supernet 192.168.96.0/21 and route to 10.1.1.30

However you can see from the traceroute, the 1st hop to 192.168.100.240 is routed to 10.1.99.198 which is not the next hop configured as static route.

Sunny

Sent from Cisco Technical Support iPhone App

Hello



Sent from Cisco Technical Support iPad App



kind regards
Paul

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future