Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

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

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
Hall of Fame Super Silver

Perhaps there is something in

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

Hall of Fame Super Silver

I am glad that my response

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

4 REPLIES
Hall of Fame Super Silver

Perhaps there is something in

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

New Member

Hi, I am learning CCNP SW.

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.

Hall of Fame Super Silver

I am glad that my response

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

Super Bronze

DisclaimerThe Author of this

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of   the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

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.

89
Views
5
Helpful
4
Replies