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WAN Failover Design

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Apr 2nd, 2009
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We are streching vlans on our WAN Layer between 2 of our datacenters terminating on 6509 via DWDM. The reason why so we can have firewalls in HA pair, one per datacenter connected via the layer vlan streched between datacenters also loadbalancers and BGP Routers. The BGP routers are IGBP peers connected to streached vlans on the same subnet.

My big concern is spanning-tree loops can affect live services.

Is cisco LAM (LOCAL AREA MOBILITY) recommended instead of streaching vlans between datacenters WAN?


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c.captari Thu, 04/02/2009 - 19:44
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I'm having a very similar issue to yours, where we don't have load balancers and some servers in 2 datacenters require to be in the same subnet, and i don't like stretching layer 2 infrastructure as this is introducing a complicated layer 2 spanning tree structure.

LAM seems an idea, but i'd be interested as well if anyone else has different oppinions

c.captari Thu, 04/02/2009 - 21:32
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By the way. There are some solutions which could work for your situation. The only problem with my situation is that the company doesn't agree with added complexity on the network. Even so , maybe it helps you:

1. If you have MPLS deployed in the backbone you can successfully use VPLS which basically extents layer 2 on top of layer 3 by using pseudo wires.

2. If you don't have MPLS , have a look into L2TPv3 which does the same thing but on top of an IP network

Giuseppe Larosa Fri, 04/03/2009 - 00:25
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Hello Francisco, Claudiu

both EoMPLS and L2TPV3 can be selective and can do their job on a per vlan basis providing flexibility.

another possible option can be that of using 802.1Q tunneling to carry all vlans inside an external 802.1Q tag between the two sites.

In this case the trunk port connected to the 802.1Q tunnel has to be configured only with the list of vlans to be extended because 802.1Q tunnel port cannot be selective

Hope to help



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