[c-nsp] IOS - Proxy arp + DAD gratuitous arp

Saku Ytti saku at ytti.fi
Wed Dec 3 02:22:27 EST 2014

On (2014-12-02 16:40 -0500), Brandon Applegate wrote:


> Could there be an older IOS (or bug) that would NOT ignore this and rather ‘answer’ for it ?  What about local proxy-arp (have never touched local proxy arp, only read about it).  I’m thinking that a proxy arp answer could trigger the duplicate IP detection in Win2k8.  No strange spanning tree errors or logs that I can see.  It could also be a ‘3rd party’ on the vlan somewhere - i.e. not the Cisco router(s).

Proxy-arp would only respond, if address is routed outside the link. So unless
the network has subnets misconfigured (perhaps /24 in one place, and say /29
in another place, proxy arp would do this, but only for the /29 part, rest of
the /24 would work ok)
Local-proxy-arp would do this for all hosts, but I doubt the network would
work at all.

> I am working with $org, but while I sit and wait on emails and pcaps - I thought I’d post this.  Thanks in advance for any brain cycles spent on it.

ACK, I think more information is required, especially how do they manually
intervene. What does ARP table say before and after this manual work?


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