Proxy-arp is used to find a router and get by on a
segment when you don't know the IP address of the
default gateway...
--- Priscilla Oppenheimer wrote:
> Hmm... That's interesting. I'm trying to figure it
> out. Say, on my office
> network, my default gateway is something like
> 10.0.0.32 because we're using
> private addresses and NAT. When I travel, would the
> router in the hotel
> respond to my ARP for 10.0.0.32?? Would the router
> think that it can reach
> network 10.0.0.0?
>
> And, let's say that I don't use private addresses on
> my office network
> (which I don't). Let's say the default gateway is
> 138.1.80.193. Would the
> hotel router respond to my ARP for 138.1.80.193?
> Would the router think
> that it can reach network 138.1.0.0?
>
> I would hate to be the desk clerk responding to
> questions about this! ;-)
>
> Priscilla
>
> At 10:56 AM 5/24/01, [EMAIL PROTECTED] wrote:
> >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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>
>
> ________________________
>
> Priscilla Oppenheimer
> http://www.priscilla.com
> FAQ, list archives, and subscription info:
> http://www.groupstudy.com/list/cisco.html
> Report misconduct and Nondisclosure violations to
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