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Re: Scenario examples for proxy arp posted 08/22/2006
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Hey there fella,

We also had another customer, who shall remain nameless, but is in the finance sector and backs onto the hotel on George Street in Edinburgh ;-)

We remotely looked after their network and we had a bag of nat'd addresses on an interface. As and when we put in static nat's, the switch would proxy arp and we'd keep monitoring...

LH


Skinner, Stephen wrote:
Leigh ,

Thanks for the detailed explanation .

I was reading the old Cisco CCIE lab workbook ( the 6 lab variant) .

And I noticed in lab 3 ,under the NAT section , it mentioned that I would
need proxy arp to complete the scenario .

I want to sure why , but after Mr Comer and yourself , I now understand why
it the natting would work without proxy arp .


Thanks again


Stephen Skinner


-----Original Message-----
From: Leigh Harrison [mailto:ccileigh@xxxxxxxxx] Sent: 22 August 2006 15:13
To: Skinner, Stephen
Cc: Cisco certification
Subject: Re: Scenario examples for proxy arp


*** WARNING : This message originates from the Internet ***

Hey there Stephen,

I've used this recently for a customer.

They moved their european datacentre to a new location and liked the idea of
having a routed LAN.  They were aloso looking to migrate from their old IP
address ranges to new ones.  The users changed straight away, but the
servers needed to stay on the old address range and the customer was quite
uncomfortable changing anything on the servers, default gateway included.

This was a bit of a problem, as they had a single switch in the top of each
rack and at the old datacentre they had a single vlan for the servers.  My
first thought was to run mobile ip with eigrp or ospf, but only standard
image switches were put in, so I only had rip to play with.

I built the whole thing routed, meaning that each switch was in it's own
L3 network, for the server switches I put in static routes, effectively
advertising what servers they had connected to that switch.  There were 10
server switches in all, all holding the same IP address, so that the servers
didn't have to change the default gateway.  Static routes were redistributed
into rip to advertise which servers lived where and proxy arp played the
main role, telling the server that it knew where the box it was after lived,
even though logically it was a few hops away, the server switch thought it
was on the same network.

The customer was very happy as it meant they could shift over 1 server at a
time is they wanted to.

Try it out with this scenario:-

PC 10.0.0.2/24 - - - - 10.0.0.1/24 | ROUTER1 | 11.0.0.1/24 - - - -
11.0.0.2/24 | ROUTER2 | 10.0.0.1/24 - - - - 10.0.0.3/24 PC

If you put a route on router 1 saying that 10.0.0.3 lives on router 2 and
vice versa, the 2 pc's will be able to ping eachother - the magic of proxy
arp ;-)

Hope that helps,
LH


Skinner, Stephen wrote:
Gents.

I have been recently been reading the Proxy Arp section of TCP/IP protocols (5th edition) by Comer.

And I was wondering if anyone can think of some scenario's in which this could be used .?

Many thanks


Stephen Skinner




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