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Layer 2 with OSPF area

Posted on 2014-11-05
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Last Modified: 2014-11-07
Hi there,

In my topology I have 3 separate building connected via fiber uplinks. Each building has a Layer 3 distribution switch that is part of an OSPF area 0. The ospf is configured with Layer 3 interfaces and not vlan-interfaces.

OSPF comes up fine and properly shares routing tables, but the issue i am having is with spanning a common vlan across all the buildings.

If i ping a computer in another building which is on a separate VLAN, it is no problem because of the inter-vlan routing. But if i have a computer in Building 1 on vlan 30 and a computer in building 3 on vlan 30, they do not ping.

The vlan-interface (or gateway) for vlan 30, 40, and 50 resides on one of the Layer 3 switches in the OSPF areas. Each one is basically a gateway for one of the 3 vlans.

The problem that i see is that if i try to ping a PC on vlan 30 in another building from Building 1, it shows that network as attached to building 1 and can't route out on layer 3 and there is no layer 2 trunk between the OSPF switches.

This issue will also exist when trying to get all switches on the same management vlan (200 in this case)

Any advice on how to route this or design this. we will have services that span the 3 buildings and would prefer them to be on the same vlan but it looks like i would need to setup a trunk between the OSPF switches.

thx, i have attached the topology
Routing-Example.pdf
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Question by:Graycon
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Don Johnston earned 1000 total points
ID: 40424868
You can't have the same network in two separate locations (separated by a different layer 3 network).

Well, you can, it just won't work.
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by:Akinsd
Akinsd earned 1000 total points
ID: 40425645
Don Johnson is 100% correct for the simple reason that they are no longer in a single broadcast domain

Alternatives
1. direct cabling
2. Contact your ISP and ask them for Ethernet Hand-off between the buildings.
3. Route maps in conjunction with Distribution lists if you want some adventure.
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Author Closing Comment

by:Graycon
ID: 40428882
thx guys
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