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Network hierarchical design doubts


I currently work in an SP with an IP/Tag-Switching network. I am in charge of presenting the pros and cons of introducing a new Distribution Layer. Our main driver for this new layer is to have more ports in order to aggregate new access routers but this single reason might not justify by itself the new layer.

I can clearly see some advatages of a distribution layer such as removing Internet/BGP from the core thus reducing some processing latency but would like to get some suggestions/advice in this matter.

Some URLs and whitepapers would be great as well.

Best Regards,



Re: Network hierarchical design doubts

Hi Nataniel,

The following doc has some basic info on hierarchical network design:

Also, I have found the following book to be an excellent resource for network design:

'Advanced IP Network Design' - by Russ White, Alvara Retana and Don Slice (ISBN: 1-57870-097-3). You can pick up a copy of this really cheaply second-hand on Amazon. Here's a link:

Hope that helps,



Re: Network hierarchical design doubts

"Advanced IP Network Design" has a new edition/replacement, called "Optimal Routing Design." It covers two layer hierarchies a little more thouroughly, and has some other additions/etc.

In general, hierarchy is required to design a network that scales, whether it's two, or three, layers. There are some more complex designs that can "flatten" highly layered designs, but you still have to have layers to hide information. Whether you should use a two or three layer design is based on how much information hiding you really need/want to scale the network, along with how the layering fits into the applications the network supports, etc. It's almost always better, though, to "over layer," and then to "punch holes in the layers," than to "under layer."

Without a lot of specific information on the particular design, it's hard to get into details of the "best design fit."