Proxy arp is still used on duel homed servers. Say you have an NT box that
has a NIC on two different networks serviced by two different routers that
reach different networks. You can't give the box two different default
gateways. Proxy arp is your only solution. Right ????
Tony M.
#6172
----- Original Message -----
From: Hire, Ejay
To:
Sent: Thursday, May 24, 2001 7:31 AM
Subject: RE: ARP versus Proxy-arp [7:5664]
> Proxy arp isn't dead, it is still in use very frequently on dial-up links.
> If you get a chance, dial-up to earthlink and run winipcfg. You'll see
that
> your default gateway is actually set to yourself. Their is a reasonable
> explanation of this behavior in the Sybex CCNP switch 2.0 chapter on
> redundancy.
>
> -EH
>
> -----Original Message-----
> From: Chuck Larrieu [mailto:[EMAIL PROTECTED]]
> Sent: Wednesday, May 23, 2001 10:37 PM
> To: [EMAIL PROTECTED]
> Subject: ARP versus Proxy-arp [7:5664]
>
>
> At the risk of becoming another Bob Vance......
>
> I'm reading Doug Comer's TCP/IP reference, on the assumption that it can't
> hurt to really get into how TCP/IP works.
>
> Proxy-arp versus normal arp.
>
> A host does not know the physical address of another host so it sends out
an
> ARP request. If the host in question lies on another network, a router
> responds to that request. Proxy ARP, correct?
>
> A host through it's TCP stack does the XOR and determines that a host lies
> on another network. The host therefore sends the packet to the device
> indicated as its default gateway in its configuration. It sends an ARP
> request for the MAC of the default gateway. Normal ARP?
>
> So in other words, proxy arp may be viewed as something of an obsolete
> protocol / operation in that most modern TCP stacks contain the mechanisms
> for doing the network XOR determination, and then using the default
gateway.
> A modern stack would recognize that a host is on a different network and
go
> the default gateway route, so to speak.
>
> In other words, the necessity for proxy arp is eliminated for the most
part
> because of the default gateway concept and the modern TCP stack.
>
> Has it sunk through this thick head finally?
>
> PS Comer states that proxy arp is aka arp hack. :->
>
> Chuck
>
> One IOS to forward them all.
> One IOS to find them.
> One IOS to summarize them all
> And in the routing table bind them.
>
> -JRR Chambers-
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