×

Warning message

  • Cisco Support Forums is in Read Only mode while the site is being migrated.
  • Cisco Support Forums is in Read Only mode while the site is being migrated.

Local Area Mobility?

Unanswered Question
Mar 28th, 2014
User Badges:

Has anyone setup basic LAM (Local Area Mobility) I have read a few different white papers on the setup and tried it in a lab with no success at all.

I've set ip mobile arp on the interface and enabled proxy-arp on it as well. I went ahead and setup redistribution of mobile into OSPF and I dont even see the routes with an "M" identifier? Am I missing something or are there known issues with this technology?

Any help is appreciated!

Thanks,smiley
 

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (1 ratings)
Loading.
Steve Fuller Fri, 03/28/2014 - 11:26
User Badges:
  • Blue, 1500 points or more
  • Community Spotlight Award,

    Member's Choice, September 2015

Hi,

I've used LAM a fair bit, albeit with EIGRP as the IGP, and from the sounds of it you've got most, if not all, of the boxes ticked. The usual problems I've seen are ip proxy-arp not being configured on the interface, and/or the redistribute mobile command missing from within router <igp> context.

So my basic configuration is as follows:

!
ip access-list standard MOBILE-DEVICES-ALLOWED
 permit any
!
router eigrp <eigrp_as>
 redistribute mobile
 default-metric <bandwidth> <delay> <reliability> <load> <mtu>
!
interface vlan <vlan_number>
 ip mobile arp timers 5 20 access-group MOBILE-DEVICES-ALLOWED
 ip proxy-arp
!

 

For the ip proxy-arp command make sure this is configured on both the router hosting the "home subnet" and the router running LAM. Otherwise hosts that are still on the home subnet will not be able to talk to the server you've migrated.

I don't think I've ever seen any host routes appear as mobile routes, but you should at least see them in the ARP table i.e., if you run sh ip arp <migrated-ip> on the router your configuring with the ip mobile arp command, you should see an ARP entry for the IP you're migrating.

A couple of points of note on that though:

  • The end system hosting the migrated IP address must generate some traffic sourced from the migrated IP address, otherwise the ARP entry will never be created.
  • The router which will be running LAM uses proxy ARP to install a host route of the migrated IP address, and this is then advertised as a /32 within your IGP. For proxy ARP to function that router must see a route to the "home subnet" e.g., a /24 subnet where the migrated IP would normally reside. If that shorter prefix route isn't there then the router running LAM won't respond to the ARP, and no ARP entry equals no host route.

 

While LAM works (honestly it does) you should obviously consider the age of the protocol and whether it'll be supported long term by Cisco. I've used it for many years in Catalyst 6500, but we've noticed it's now only supported on the "richer" feature sets i.e., Advanced IP services, and it's never been included within the Cisco Nexus product line and never will be from what I'm told. I'd also bet it's older than some of the folk reading and answering questions in this forum so support may be tricky. See Ivan's blog post at Local Area Mobility (LAM) – the true story for some of the history.

Regards

Patrick Beaven Mon, 03/31/2014 - 06:36
User Badges:

Steve,

Thanks for the info! I think my only issue was that I dont have a route point out of the network for the /24 of that subnet. I will try this out. I dont know of any other technology like this is I've used IPSLA and conditional advertising. Do you know of any other network technology that can accomplish the same thing other than VPLS and Conditional advertising?

Patrick Beaven Mon, 03/31/2014 - 07:11
User Badges:

 Have you seen anyone try to use this feature with VMware guest vm's?

 

Steve Fuller Mon, 03/31/2014 - 07:36
User Badges:
  • Blue, 1500 points or more
  • Community Spotlight Award,

    Member's Choice, September 2015

Hi Patrick,

I've seen it used primarily for DR purposes, and migrated IP addresses from SQL databases, NAS and guest VM's hosted on VMware ESX clusters.

When VMs are migrated these are not a live vMotion. There's storage replication going on in the background to replicate the VMDK images and it's simply a case of bringing up the VMs in the alternate data centre on another ESX cluster.

I'm not sure if VMware still has the requirement, but it used to be that vMotion was only supported if the VMkernel interface of the ESX hosts were in the same Layer-2 domain. We don't have that capability and so live vMotion was not used.

It's worked reasonably well over the years although we expect to retire the functionality in the near future as we are now moving to a Cisco OTV (Overlay Transport Virtualisation) based solution as the data centre routers are migrated to Cisco Nexus.

Regards

Patrick Beaven Mon, 03/31/2014 - 08:40
User Badges:

Steve,

Yes i could see some environments using the OTV option and the backend vmdk's and all storage is already replicated and local to the router. I wonder if it even works with the vm hosts as the host server tend to cache arp entries and I have not been able to get it working on any environment with vmware yet.. I didnt know if there is any known tweaks to make it work within a vm environment?

Steve Fuller Mon, 03/31/2014 - 09:09
User Badges:
  • Blue, 1500 points or more
  • Community Spotlight Award,

    Member's Choice, September 2015

The only tweak that I’ve come across is to clear the ARP cache on the servers, both the migrated server i.e., on the VM you’ve moving, but also on any hosts remaining on the “home” subnet. If you don’t do this then when the migrated VM tries to communicate with hosts that are still on the home subnet, it’ll use their real MAC address rather than the MAC address the router.

On most server OS the ARP cache aging time is pretty short e.g., 10-miniutes, and so this can have already aged out by the time you’ve migrated the IP to the new data centre. We also tend to clear the ARP cache on the routers as these were much longer and so may not have aged out naturally.

Do you actually have LAM working now i.e., you can see an ARP entry for the migrated IP and you’ve got the host route of the migrated IP address in your IGP?

Regards

Actions

This Discussion