At 05:05 PM 5/25/01, Bob Vance wrote:
>Once the Proxy ARP answers the client's request for his
>DG on net 10, then all the other packets will be to "real" Internet
>addresses.
OK, I hear you on the routing questions, but it turns out the router does
NOT respond to the ARP for the DG. I decided to try it. It doesn't work for
a different reason than expected.
I left my PC configured as I use it on a real network and plugged it into
my lab network, which uses a different addressing scheme. I was emulating a
traveller connecting to the hotel network without reconfiguring the TCP/IP
control panel.
I had debug arp on and here was the result:
IP ARP req filtered src 10.0.0.2 0000.0ed5.c7e7, dst 10.0.0.1 0000.0000.
0000 wrong cable
The router won't respond to an ARP from a station that isn't on its subnet.
Remember that an ARP packet has the sender's IP address in it. I was
running 11.0 because my lab network is old so your results may vary.
I think the hotel network is on fantasy island. ;-)
Priscilla
>-------------------------------------------------
>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: Friday, May 25, 2001 3:04 PM
>To: [EMAIL PROTECTED]
>Subject: RE: ARP versus Proxy-arp [7:5664]
>
>
>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:
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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
>FAQ, list archives, and subscription info:
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>Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
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