arp: is on lo0 but got reply from...

Modulok modulok at
Mon Oct 29 23:42:33 PDT 2007

One of my FreeBSD machines acts as a router, providing shared internet
access via ipfw/natd to the local network. Recently I've been getting
a lot of these in the logs:

    arp: is on lo0 but got reply from (someEthernetAddress) on xl1

xl1 is my Internet-facing interface. The address is
configured on the internal interface, xl0 not xl1. The address mapping
for is a permanent entry in the ARP table. 1) After
reading the arp(4) manpage am I to assume that someone on my ISP's
side of things has something terribly mis-configured? 2) If the local
host has a permanent entry for, why would it send out an
arp request for an address it already knows (is this normal)?

Just trying to make sure it's not something I screwed up...

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