nanog mailing list archives

Re: Proxy ARP detection (was re: best practice for advertising peering fabric routes)


From: ML <ml () kenweb org>
Date: Wed, 15 Jan 2014 23:49:15 -0500


On 1/15/2014 6:31 PM, Clay Fiske wrote:
Yes, yes, I expected a smug reply like this. I just didn’t expect it to take so long.

But how can I detect proxy ARP when detecting proxy ARP was patented in 1996?

http://www.google.com/patents/US5708654


Seriously though, it’s not so simple. You only get replies if the IP you ARP for is in the offender’s route table (or 
they have a default route). I’ve seen different routers respond depending on which non-local IP was ARPed for. And 
while using something like 8.8.8.8 might be an obvious choice, I don’t care to hose up everyone’s connectivity to it 
just to find local proxy ARP offenders on my network.

-c


Shouldn't ARP inspection be a common feature?


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