If a router running Proxy ARP didn't have a "route of last resort" or
"default route" would it still respond to an ARP for some random non-local
network? It would cause problems if it responded to the ARP when it
couldn't really route packets to the destination. I suppose it usually
works because this router or the DG as you mention below has a default
route to the rest of the world.
And how about network 10.0.0.0? The hotel router in the scenario wouldn't
respond to a customer's ARP for a DG of 10.0.0.1 unless the hotel network
was configured with a 10.0.0.0 network, would it? Or maybe the default
route would cover this too, but maybe not since it's a private address.
I realize I'm being brain damaged about the whole topic, but I think the
issues are more subtle than people realize.
Priscilla
At 09:14 PM 5/24/01, Bob Vance wrote:
> >Why would it think it can get to 10.0.0.0 (that ones a little
> >easier) or 138.1.0.0 (unlikely) when the client computer ARPs for its
> >default gateway?
>
>Well, now.
>Does a DG of its own count as "knowing how to get there"?>)
>
>
>-------------------------------------------------
>Tks |
>BV |
>Sr. Technical Consultant, SBM, A Gates/Arrow Co.
>Vox 770-623-3430 11455 Lakefield Dr.
>Fax 770-623-3429 Duluth, GA 30097-1511
>=================================================
>
>
>
>
>
>-----Original Message-----
>From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
>Priscilla Oppenheimer
>Sent: Thursday, May 24, 2001 6:24 PM
>To: [EMAIL PROTECTED]
>Subject: RE: ARP versus Proxy-arp [7:5664]
>
>
>You missed the point. I know what Proxy ARP is.
>
>I assume the goal is that the traveller doesn't need to do any
>reconfiguration and can leave the default gateway set to the home office
>setting of 10.0.0.32, or 138.1.80.193 in my second example. A router
>doesn't just blindly respond to ARPs. It only responds if it thinks it
>can
>get there. Why would it think it can get to 10.0.0.0 (that ones a little
>easier) or 138.1.0.0 (unlikely) when the client computer ARPs for its
>default gateway?
>
>The design of the hotel network must be quite interesting. I was hoping
>the
>original poster had more details.
>
>Priscilla
>
>At 12:35 PM 5/24/01, Cornell Manea wrote:
> >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-
> > > >FAQ, list archives, and subscription info:
> > > >http://www.groupstudy.com/list/cisco.html
> > > >Report misconduct and Nondisclosure violations to
> > > [EMAIL PROTECTED]
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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
> >[EMAIL PROTECTED]
> >
> >
> >__________________________________________________
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>
>
>________________________
>
>Priscilla Oppenheimer
>http://www.priscilla.com
>FAQ, list archives, and subscription info:
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________________________
Priscilla Oppenheimer
http://www.priscilla.com
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