Distribution-to-Distribution Link Design Layer 2 or Layer 3?

[Meddane]

Sometimes network engineers underestimate the importance of the interconnection link between the distribution layer switches at the distribution block of the enterprise campus network. There are two options to design the Distribution-to-Distribution Link:

-Layer 2

-Layer 3

What are the benefits and the disadvantages of both?

[balaji.bandi]

In shorts depends on requirement and design.

-Layer 2

- If you like to extend the VLAN Across the network, so any Access can carry all the VLAN required.

- Also you need to consider how your Core integration? is this layer 2 or Layer3

- Spanning tree need to consider here. (big evil if you do not plan properly)

- You can not use both uplinks, one will be blocking state. ( if you deploying VSS or SWV is different case).

-Layer 3

- The benefit of running layer-3 between your distribution devices is that you do not have to worry about running spanning tree protocol since there is no loop in your network vs in a layer-2 design you would need to run STP.

- in this case, only the Access switch will be Layer 2

- this has more advantages you can do equal path load balance between Distribution

- easy to troubleshoot and fix the issue, since the Layer 2 broadcast domain is limited to access switch only

-  The disadvantage you can not extend Layer 2 here.

Trends are moved hee especially with DNAC and Cat 9K different  - Moving to a New World. everything will be Layer 3 with DNAC and VXLAN/LISP

[Leo Laohoo]

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@Meddane wrote:

There are two options to design the Distribution-to-Distribution Link:

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That is a trick question without understanding how realistic the underlying network is.  

If we are just playing paper "what-ifs" scenario then Layer 3 is my preference because it can scale and scale up quickly.  

The major pull-back for a Layer 3 distro/core are: 

1. Cost
2. Technical knowledge
3. Cost
4. Cost
5. Cost