From: Higgins, Andrew (Andrew.Higgins@xxxxxxxxxxxxxxxxxxx)
Date: Thu Jul 01 1999 - 13:36:50 GMT-3
If a router has an interface on say 192.168.1.0/24 and it sees an ARP on the
subnet for, say, 192.168.2.1 it knows that the device is not using the same
subnet mask as everyone else. Since the router knows the 192.168.2.0 subnet
is not local, and the router does know how to reach that segment, it will
reply to that ARP with its own MAC address. The device will think it's
talking directly to 192.168.2.1 when actually the router is receiving the
packets and then forwarding the appropriately.
Hope that helps.
Andrew
-----Original Message-----
From: Muralidhar Devarasetty [mailto:dhar_murali@hotmail.com]
Sent: Thursday, July 01, 1999 12:41 PM
To: mdetrick@cisco.com; Andrew.Higgins@sequoia.panurgy.com;
jbxu@www3.cea.online.sh.cn; ccielab@groupstudy.com
Subject: Re: proxy-arp
Mark,
Do U mean Router will process (when proxy-arp is enabled) for every arp
requset send on the segment,so that it can send its MAC address for the
destination it can reach.Please explain...
Thanks in advance..
Murali
----Original Message Follows----
From: "Mark, Detrick" <mdetrick@cisco.com>
Reply-To: "Mark, Detrick" <mdetrick@cisco.com>
To: "Higgins, Andrew" <Andrew.Higgins@sequoia.panurgy.com>, "'jbxu'"
<jbxu@www3.cea.online.sh.cn>, <ccielab@groupstudy.com>
Subject: Re: proxy-arp
Date: Mon, 21 Jun 1999 09:47:09 -0700
In addition to the great answer below...
The default-gateway setting on the PC tells the PC to send an ARP for the
local MAC of the destination machine on its own subnet or to send to the MAC
of the IP address of the default-gateway because the machine is not on the
local subnet. Determining if the machine is on the local subnet is
accomplished by a calulation using the subnet mask and IP address of the PC.
Example:
If you wanted to use the router as a proxy-arp instead of gateway on the PC,
and the enterprise was addressed using private 10. A computer on segment
10.0.0.0/24 may be configured with i.e. 10.0.0.56/8 (opening up the subnet
mask to make the PC think all the subnets are local, router is configured
with 10.0.0.1/24) and send all 10 traffic out on its local subnet. This
might work for all 10 addressing within the enterprise, but resolution to
anything other than 10.0.0.0 (outside the enterprise)would fail because the
PC would want to send to the gateway which has not been configured.
Mark Detrick
DSL Business Unit
Cisco Systems
2569 McCabe Way
Irvine, CA 92614
----- Original Message -----
From: Higgins, Andrew <Andrew.Higgins@sequoia.panurgy.com>
To: 'jbxu' <jbxu@www3.cea.online.sh.cn>; <ccielab@groupstudy.com>
Sent: Saturday, June 19, 1999 7:30 PM
Subject: RE: proxy-arp
> Not necessarily. For proxy-arp to work, a device needs to arp on the
local
> subnet with a destination address that is not part of the local subnet.
I
> have seen proxy-arp used at a client site where several Unix workstations
> had the incorrect subnet mask configured and they were sending arps on
the
> local subnet for devices that were actually on remote subnets. The
router
> recognized the arps were for remote subnets and replied to the
workstations
> with its own mac address, then passed to data along to the remote device.
>
> Andrew
>
> -----Original Message-----
> From: jbxu [mailto:jbxu@www3.cea.online.sh.cn]
> Sent: Saturday, June 19, 1999 10:13 PM
> To: ccielab@groupstudy.com
> Subject: proxy-arp
>
>
> question:
> I think "proxy-arp" is to help pc with no knowledge of routing
> to determine the media address of pc on other networks.I know the proxy
> arp on the cisco router is enabled by default.
> Is this mean I can ping a pc on another network from my pc without
> defult-gateway.
> anyone have the experience to use the proxy-arp?
>
> thanks in advance
>
>
> jbxu
> jbxu@mail.cea.online.sh.cn
>
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