[nsp] ARP errors!!!!

[james at thehamptonfamily.us]

We didnt have proxy-arp, but what we do have is an Ethernet port on the
router b with a bunch of secondary addresses instead of vlans (I know this
is real ugly but I inherited this mess and its on my list of things to
re-design). This means that its one big broadcast domain. They used to
have one of the 209.45.x.x addresses on the "router a" side but removed it
last night because it was no longer in use, this is likley when the
problems started. This had had the effect of making things work but for
the wrong reason, when a request came in for 209.45.x.x "router a" saw
that it had an entry in its arp table and thought the route was directly
connected and didnt use the default route, when there was a 209.45.x.x
host on the ethernet port "router a" sent the traffic through that
ethernet port, when that was removed the router didnt use the default
route like it should because it still had 209.45.x.x addresses in its arp
table. I think this is what was happening, i have plenty of work ahead to
staighten things out.

james
>
> On Tue, 25 May 2004 james at thehamptonfamily.us wrote:
>
>> My router is suddenly entering into its arp table address from other
>> subnets that it has no interfaces in.
>>
>> TLTOLOH-6400-0-NRP1#show ip arp
>> Protocol  Address          Age (min)  Hardware Addr   Type   Interface
>> Internet  209.45.x.2x          0   0003.fed5.8000  ARPA
>> FastEthernet0/0/0
> [----]
>> May 25 12:37:48: IP ARP: rcvd req src 64.254.b.x 0003.fed5.8000, dst
>> 64.254.b.y FastEthernet0/0/0
>
> This is how Cisco behaves. It enters MAC immediately to ARP table if it
> gets ARP request from this MAC and gets IP address from that packet.
>
> In your case there may be some shared medium (ethernet with more than
> one subnet) or some router does proxy ARP or something like that. It is
> even possible that some node on that ethernet forges packets but if
> these MACs  really exist somwhere else then it should be proxy ARP.
>
> I have used this 'feature' to switch over IP address from one server to
> another in HA environment using send_arp program by Yuri Volobuev :-)
>
> ---
> Cougar