IP Arp mobile

[lwhalley]

We are using IP mobile arp to keep from having to change static IP addressing on printers and servers during a multi-phase move.

We have put in a global command of "bridge 1 protocol ieee"

We have the commands:

ip mobile arp access-group 41

bridge-group 1

under the Fast Ethernet interface.

We use EIGRP and have a command of "redistribute mobile metric 1000000 10 250 250 1500" under it.

My question is this - do the subnets that are to be "mobile" need to be configured under both router's (old and new location) fast ethernet interfaces?

The problem we are seeing is that devices are having trouble finding their default gateway within the subnet when on the other router.

Any advice or help would be appreciated.

[vkapoor5]

Hope the following link helps....

http://www.cisco.com/en/US/tech/tk722/tk721/technologies_white_paper09186a00800a3ca5.shtml

[Richard Burts]

In my experience the bridge-group 1 and bridge 1 protocol ieee were not needed to get it to work.

You should not need to configure the subnet on both interfaces. In fact if you do configure the subnet on both interfaces it will confuse the network and liekly will break things. The whole point of mobile arp is to allow a device with a "foreign" address to co-exist on the segment and for its address to be recognized.

If you are experiencing problems where devices are not finding their default gateway, I will make a guess that you may have disabled proxy arp. For mobile arp to work correctly you will need to have proxy arp enabled.

So my suggestions are: enable proxy arp on any interface where you may have a device move located with an address that does not belong in that subnet; do not configure the subnet on more than one interface.

HTH

Rick

[lwhalley]

Since writing the original message, I did take out the bridge-group statements and it continued to work. So I agree with you that they were unnecessary. I'll check the proxy arp statements.

I also found some problems with subnet masks on devices that did not match the router entry. After correcting those, that solved some of my problems. I had to temporarily configure the subnet on the 2nd router to get to those devices to make the change, but was then able to delete it so that it is only configured in one place. It definitely caused some issues having it in both places.

So, the only problem that I still have is with the gateway and the proxy arp may solve that.

Thanks so much for the advice. The white paper isn't very clear (at least to me) on the subnet configuration. It probably assumes that basic guidelines on configuring subnets in only one router would always be followed.

[Richard Burts · Accepted solution]

Subnet masks that do not match can certainly cause problems (many of which can be solved and masked by proxy arp) and the network will generally run better when the masks do match.

Proxy arp is on by default. It is generally not needed if subnet masks are carefully configured and if end stations have the proper default gateway configured. I am seeing increasing number of customers who turn it off as part of increasing the security implementation of their routers. There are some situation and mobile arp is one of them when it really is needed (and many people do not recognize this).

HTH

Rick