Scenario examples for proxy arp
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 > > > > The Royal Bank of Scotland plc, Registered in Scotland No. 90312. Registered Office: 36 St Andrew Square, Edinburgh EH2 2YB > > Authorised and regulated by the Financial Services Authority. > > This e-mail message is confidential and for use by the addressee only. If the message is received by anyone other than the addressee, please return the message to the sender by replying to it and then delete the message from your computer. Internet e-mails are not necessarily secure. The Royal Bank of Scotland plc does not accept responsibility for changes made to this message after it was sent. > > Whilst all reasonable care has been taken to avoid the transmission of viruses, it is the responsibility of the recipient to ensure that the onward transmission, opening or use of this message and any attachments will not adversely affect its systems or data. No responsibility is accepted by The Royal Bank of Scotland plc in this regard and the recipient should carry out such virus and other checks as it considers appropriate. > > _______________________________________________________________________ > Subscription information may be found at: > http://www.groupstudy.com/list/CCIELab.html
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