[cisco-bba] How to stop static routes looping

Oliver Boehmer (oboehmer) oboehmer at cisco.com
Fri Mar 14 03:44:40 EDT 2008

Andy Saykao <> wrote on Friday, March 14, 2008 1:01 AM:

> Thanks to Oli, I implemented the command "ip verify unicast
> reverse-path" to our Virtual-Access template and it has stopped the
> routing loop.
> Interestingly enough I could only replicate the problem when the
> customer was using a Cisco product (eg: Cisco 827) and did not
> configure the additional subnet on their Ethernet interface. This
> resulted in a loop back and forth between the customer's network and
> our LNS. This was before I used the "ip verify unicast reverse-path"
> command. 
> However, when using non-cisco product like a Netcomm NB1300 or Siemens
> 6520, and not having configured the Ethernet interface with the
> additional subnet on these devices, they did not show the same routing
> loop problem. Somehow these devices stopped the routing loop from
> happening.
> Why would this be the case whereby the routing loops are only occuring
> on the cisco 827 as illustrated above?

I have no clue. It sounds like an "intelligent" behaviour, but still
strange as I would expect a router to consult its routing table and act


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