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"non-issues" when provoking a CDP routing loop

For fun, i decided to create a little lab and do some troubleshooting regarding routing loops.

As a template I used this setup by cisco and do some experimenting with 12.4 and 15.2 IOS routers.

My result was somewhat annoying, as I couldn't get the loop to manifest. E.g., the traceroute went through R1 - R2 - R4 just fine.

When following the "Troubleshoot" commands, I noticed some information missing with

show ip cef 10.10.34.4 detail

 E.g., adjacencies were not listed. So is my assessment correct that this routing loop with CEF only appears in older IOS versions and newer versions just have appropriate safeguards in place? Or do I have to assume the lab is simply "broken" in that it fails to produce the expected outcome and everything works just fine?

 

Thanks for your time.

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VIP Mentor

Re: "non-issues" when provoking a CDP routing loop

Hello,

 

I tried to recreate the setup as good as possible (since the configs of R3 and R4 are missing). I cannot even recreate the loop, I don't see how the loop occurs since the static routes only come into play when the BGP learned routes are not there. 

Honestly, the document is from 2005, so it might indeed be IOS specific or CEF/BGP version specific. I am using 15.6(2) in GNS3 by the way...

1 REPLY 1
VIP Mentor

Re: "non-issues" when provoking a CDP routing loop

Hello,

 

I tried to recreate the setup as good as possible (since the configs of R3 and R4 are missing). I cannot even recreate the loop, I don't see how the loop occurs since the static routes only come into play when the BGP learned routes are not there. 

Honestly, the document is from 2005, so it might indeed be IOS specific or CEF/BGP version specific. I am using 15.6(2) in GNS3 by the way...

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