Proxy-Arp Lives!
I have to add that as I understand it proxy arp and nat are how hotels offer
internet connectivity. Take a laptop with any ip address configured plug it
in and it will arp for its default gateway. The router with proxy arp will
answer as the default gateways mac address. Then using a wide scope for nat
(the scope would be the entire ip address range) the hotel can provide
internet connectivity to a client with any configured ip address and
gateway.
Dean Whitley
-----Original Message-----
From: Hire, Ejay [mailto:[EMAIL PROTECTED]]
Sent: Thursday, May 24, 2001 10:32 AM
To: [EMAIL PROTECTED]
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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