detecting routing loops

[duster]

what the easiest way to detect a routing loop on my cisco network. I figured tracert can help but should i look for and what other tools can i use?

[kevon]

Isn't tracert a dos command and not recognized by cisco devices?

[duster]

Isn't tracert a dos command and not recognized by cisco devices?

yeah but if you use it to send packets you can see the destinations. and next hops

[tshi5791]

Hi Duster,

What type of network do you have (i.e. how many switches L2,L3, and routers)? What type of routing protocol are you running? And yes from your workstation you can detect a loop using tracert.

[duster]

Hi Duster,

What type of network do you have (i.e. how many switches L2,L3, and routers)? What type of routing protocol are you running? And yes from your workstation you can detect a loop using tracert.

I was just asking how to find it in general. but my senerioa, l3 switches and 6 regional routers running eigrp

[tshi5791]

Oh yes, traceroute (from the devices) or tracert from your Windows box will show you where the loops occur.

[duster]

Oh yes, traceroute (from the devices) or tracert from your Windows box will show you where the loops occur.

Ok what do i specifically look for in the tracert responses?

[dalybrian]

The loop will be bounce between interface / ip address until the trace route is completed ( 30 hops ).

I wish i had an example to show you however if you have a trace route that you can send us with where you think it is looping we can tell you for sure.

[tshi5791]

Yes, you will see something like this:
H:\>tracert 10.64.3.7

Tracing route to 10.64.3.7 over a maximum of 30 hops

1 <1 ms <1 ms <1 ms 10.64.148.253
2 <1 ms <1 ms <1 ms 10.64.200.233
3 2 ms 2 ms 2 ms 192.168.147.1
4 2 ms 2 ms 2 ms 10.200.5.62
5 2 ms 2 ms 2 ms 192.168.147.1
6 2 ms 2 ms 2 ms 10.200.5.62
7 2 ms 2 ms 2 ms 192.168.147.1

and this scenario will keep repeating itself.

regards,