[c-nsp] Proxy ARP -- To disable, or not to disable..

[Julio Arruda]

Saku Ytti wrote:
> On (2008-03-22 12:16 -0400), Julio Arruda wrote:
>  
>> I do remember one specific topology (DMS switches with EIUs and etc), 
>> where proxy-arp was used as a requirement in some configurations.
> 
> I can't think of single reason why you'd need proxy-arp, ever.
> However, for residential connections local-proxy-arp is commonly needed feature
> and for some cruel and unusual reason local-proxy-arp does not work without
> having proxy-arp also on (at least this was the case in 12.2SB, hopefully
> fixed since, didn't bother opening DDTS, but just as writing this, I
> checked for DDTS and fond CSCds43725, no fixed IOS' so far)
> 

The IP stack in the EIU, the ethernet ports in the DMS, was not exactly 
very nice, from what I remember.

You would have the 'external side' of the EIU and the internal side, in 
the same "subnet", and would play with proxy arp to provide a 'flat 
subnet' to the CM, I don't have access to the EUI manuals anymore, but 
others may want to take a look (or not, since it would be risking some 
heavy damage to brain cells).

And, on the way out, something similar would come into play, at least in 
older sw.
The Bay routers would not have proxyarp enabled by default, so we had to 
enable it to make it work.

I've seen another use (or misuse) of proxy-arp, something like pointing 
the static route in a router, to the ethernet port, not the next-hop.
This would make the router arp for everything on that port to reach that 
route, so, depending in proxy-arp.
Yes, it is weird..but others here with more IOS background may be able 
to ellaborate on that.