[163327] in North American Network Operators' Group
Re: IP4 address conservation method
daemon@ATHENA.MIT.EDU (Dan White)
Wed Jun 5 14:43:24 2013
Date: Wed, 5 Jun 2013 13:42:53 -0500
From: Dan White <dwhite@olp.net>
To: Mikael Abrahamsson <swmike@swm.pp.se>
In-Reply-To: <alpine.DEB.2.00.1306051856040.12285@uplift.swm.pp.se>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On 06/05/13 18:57 +0200, Mikael Abrahamsson wrote:
>On Wed, 5 Jun 2013, William Herrin wrote:
>
>>Nothing. The problem is that the arp source IP doesn't fall within the
>>interface netmask at the receiver. Some receivers ignore that... after
>>all, why do they care what the source IP is? They only care about the
>>source MAC. Other receivers see a spoofed packet and drop it.
>
>Why wouldn't it be within the source IP mask? I would imagine
>local-proxy-arp would work exactly the same way as if a directly
>connected host with the IP the ARP request was for would have
>answered.
I've seen two vendors get it wrong: 1) when originating an ARP request, the
router uses a source IP that does not match the subnet of the ip being
requested (happened when the interface on the router had secondary IPs); 2)
when a customer had more than IP address assigned on an interface/VLAN, and
one device ARPd the other, the router responded with its own MAC, creating
a race condition where sometimes traffic between those two devices was
forced up through the router.
--
Dan White
