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In a huge campus network design, should be the Core layer operate on L3 if the Distribution is operating on L3?

Istvan kelemen
Level 1
Level 1

Or the routing overhead is less if the Core is operating on L2?

 

For example:

 

Wan routers and Dist L3 switches connect to Core switches (L2)

Access layer L2 switches connects to Dist.

 

So Access layer SW's do Diffserv marking, Dist layer switches do queuing, the inter vlan routing as well as routing and the core only forwards traffic based on L2.

 

Is it a valid design? Should the core also have QoS?

 

Thanks!

2 Accepted Solutions

Accepted Solutions

Richard Burts
Hall of Fame
Hall of Fame

Perhaps there is something in your perspective that I am not understanding. But from my perspective the core should ALWAYS operate at layer 3.

 

HTH

 

Rick

HTH

Rick

View solution in original post

I am glad that my response was helpful. Thank you for using the rating system to mark this question as answered.

 

I have a couple of comments about this:

- The CCNP materials have some materials that look back to how things used to be as well as some materials that look forward at how things should be currently and in the future. Sometimes it is difficult to differentiate which are the historic aspects and which are the current/future aspects.

- We should differentiate between learning that things COULD be in a certain way and things SHOULD be in a certain way. So I would suggest that the core COULD be layer 2 but that it SHOULD be layer 3.

 

HTH

 

Rick

HTH

Rick

View solution in original post

4 Replies 4

Richard Burts
Hall of Fame
Hall of Fame

Perhaps there is something in your perspective that I am not understanding. But from my perspective the core should ALWAYS operate at layer 3.

 

HTH

 

Rick

HTH

Rick

Hi,

 

I am learning CCNP SW. There is written, Core layer can operate both L2 and L3.

From my point of view L3 core is also better.

I am glad that my response was helpful. Thank you for using the rating system to mark this question as answered.

 

I have a couple of comments about this:

- The CCNP materials have some materials that look back to how things used to be as well as some materials that look forward at how things should be currently and in the future. Sometimes it is difficult to differentiate which are the historic aspects and which are the current/future aspects.

- We should differentiate between learning that things COULD be in a certain way and things SHOULD be in a certain way. So I would suggest that the core COULD be layer 2 but that it SHOULD be layer 3.

 

HTH

 

Rick

HTH

Rick

Joseph W. Doherty
Hall of Fame
Hall of Fame

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Yes, you can have a L2 core, but as Rick has noted, modern designs lean toward L3 cores.

There are, even today, pros and cons to each, but the biggest factor would be a modern L3 core would normally use L3 switches, rather than traditional routers.  Generally you want the core to move packets as quickly as possible, and L2 switches were generally better at that than "traditional" routers.  L3 switches, though, have nearly L2 switch performance, so the performance difference isn't much of issue any longer (especially with CEF L3 switches and/or MPLS).

BTW, not something you'll see in many current design documents, but modern L3 switches are so powerful and support so many ports, that you might have distribution and access just L2.

If you're doing QoS, yes I would recommend it also be enabled in the core too, L2 or L3.

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