Best Redundant Core design - Layer 2 or Layer 3 or workable combo

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Jun 25th, 2007
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Dual 6506 IOS switches in each of two buildings (A1,A2,B1,B2). Dual 3750 IOS switches in each of two other buildings (C1,C2, D1,D2). Each building pairs are will run HSRP to the LAN segments. Each pair is also tied to another building pair for MAN redundancy (ie. A1 ties to B1 and C1, A2 ties to B2 and C2, B1 also ties to D1, B2 also ties to D2; if A1B1 link goes down A2B2 will take over). Need to provide a VLAN or two that spans the 4 locations for layer 2 needs such as maintaining server cluster heartbeats between servers dispersed between buildings. Need to maintain MAN redundancy between buildings and route traffic from one building's LANs to another. What's the best way to handle this?

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Anonymous (not verified) Fri, 06/29/2007 - 10:13
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Try creating a dot1q tunnel in between which is a better way of implementation

royalblues Fri, 06/29/2007 - 10:21
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If you require the same VLANS to be present across the buildings, then the connection would be L2 (sort of collapsed core)


If the above requirement is not necessary, then you should use L3 links between the cores as this will reduce the broadcast domain and also improve convergence


HTH

Narayan

dhopkins2620 Fri, 06/29/2007 - 10:42
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We do require that the same VLANS be present across buildings. L2 (collapsed core) is what I was trying to avoid if possible. How then do I handle the redundancy with the cores between buildings that would have been handled with OSPF L3 links?

royalblues Fri, 06/29/2007 - 10:46
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If you require the same vlans to be present across the buildings, then you would have to create a collapsed core. you cnnot have a L3 seperation between the same VLANS over two buildings


HTH

Narayan

dhopkins2620 Fri, 06/29/2007 - 11:16
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I understand. I will try to clarify. One VLAN will be present across the buildings to maintain the heartbeats (L2). For example, one NIC on a server in Building A is on the same vlan as a NIC on a server in Building B. I have other VLANs (or subnets)that are only local to each building. For example, server in Building A has a second NIC attached to a LAN in Building A.


In this collapsed L2 core, the management/failover of the core switches between buildings will be on a seperate VLAN across the buildings. This VLAN would be different than the heartbeat vlan. How do I handle the failover functions in L2?

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