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Beginner

Same hop IP address in two separate hop

Hi All,

Can anyone help me to understand the issue what is happening here for below traceroute issue ? I am getting same hop IP address in hop 2 and 4. As from the trace report it seems 2 routers are showing each other as next hop for same destination but if it happened then a routing loop would occur but no routing loops there. Would be obliged if anyone can clarify the issue here and if possible share a sample topology with configuration / lab.

Test-RT#traceroute 10.8.4.15
Type escape sequence to abort.
Tracing the route to 10.8.4.15
VRF info: (vrf in name/id, vrf out name/id)
1 172.3.1.17 0 msec 0 msec 0 msec
2 172.18.17.15 12 msec 12 msec 8 msec
3 172.18.17.16 16 msec 8 msec 12 msec
4 172.18.17.15 12 msec 12 msec 8 msec
5 172.18.8.9 16 msec 8 msec 16 msec
6 10.87.25.78 8 msec 12 msec 12 msec

[**] 172.18.17.15172.18.17.16 are point-to-point link between two routers. where 172.18.17.16 is under my administration but 172.18.17.15 is not under my administration. So if you ask for configuration of 172.18.17.15 then I could not provide you.

BR//

Olly

7 REPLIES 7
VIP Advisor

It could be a loop or

It could be a loop or misconfiguration on the other end. 

Is this router Test-RT under your management? This router 172.18.17.16 is sending back the packet, do you have any default route on this router, you could verify it through:

show ip cef

show ip cef exact-route <source> <destination>

Beginner

Hi Moisa,

Hi Moisa,

Thanks for your reply. Your required information is given below inline.

Is this router Test-RT under your management?

  • Yes

do you have any default route on this router, you could verify it through:

  • MP_FW#show ip cef vrf V90 10.8.4.15
    10.8.4.0/27
    nexthop 172.18.17.15 Vlan90

    MP_FW#show ip cef vrf V90 exact-route 172.3.1.158 10.8.4.
    172.3.1.158 -> 10.8.4.15 => IP adj out of Vlan90, addr 172.18.17.15

Beginner

There might be a chance that

There might be a chance that hop

3 172.18.17.16 16 msec 8 msec 12 msec

is having destination nat configured

Highlighted
Beginner

HI ROHANTARDEKAR,

HI ROHANTARDEKAR,

Thanks for your response.

"3 172.18.17.16 16 msec 8 msec 12 msec

is having destination nat configured"

No, NAT is not configured.

BR//

Olly

VIP Engager

can you share your routing

can you share your routing configuration from all routers?

Regards,

Deepak Kumar 

Regards,
Deepak Kumar,
Resume duty after a long holiday
Beginner

Hi Deepak,

Hi Deepak,

I just manage 172.18.17.16 device.

Contributor

I would suggest to run

I would suggest to run traceroute from an end host and fire up wireshark for packet analysis. This could be a software error. If next hop router was configured to send the packets back to you then packet would never reach destination unless there is a redudant path, but with traceroute results that doesn't seem to be the case.

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