Mailbag: When to use Layer 3 in wiring closets

Last time, we heard from many readers who refuse to buy into the notion that using Layer 3 technology in the wiring closet is a good idea. Today, we hear from some believers.

One reader says that several years ago he went from the flattest of flat networks to one with routing in the wiring closets:

“Reflecting back at the problems with the bridge network, I decided to [embark] on an IP scheme that allowed around 500 nodes in a broadcast domain and pushed routing to the wiring closet. Our equipment can easily handle the number of routes in the routing table without any summarization. We can easily identify the exact location of a node from its IP address. We have more flexibility using [quality of service] and [access control lists] with L3 at the edge. L3 at the edge has helped in troubleshooting and has contained misconfigured hosts. If VoIP became a reality in my company, we would add QoS to the routers for those packet types to address latency and jitter.”

Another says his university system is planning a big network upgrade by 2006, with lots of Layer 3:

“I believe Layer 3 hardware and good knowledge of how to design, implement and manage in a Layer 3 environment will be necessary if you are going to mix applications that require QoS and a lot of bandwidth…. Network-based videoconferencing and telephony, along with movement of massive data files developed in the basic science research will be supported by these networks – LANs, [campus area networks] and WANs. Layer 3 will play a big role at the edge of these networks in the [intermediate distribution facilities] as well as in the core.”

Another big move is planned by a school in the U.K., which currently has separate networks – one for curriculum and one for administration:

“The main reason they are completely separate at the moment is security, although that causes an administrative nightmare and limits the operations available. So we are looking for Layer 3 switching using the HP Procurve 4100gl series. In theory we are going to maintain the security and be easier to manage. But as you said in your article it takes lots of preparation, design and money. Let’s hope everything will be OK.”

It seems that whether you use Layer 3 in the wiring closet depends both on the kinds of applications you are running and on what Layer 2 alternatives are available to you. Big thanks to everyone who wrote in.