Re: L3 switches-> Efficient bandwidth utilization, for Campus network

On Apr 19, 8:45 am, "Scooby" <mmscoo...@xxxxxxxxxxxxx> wrote:
<qazmlp1...@xxxxxxxxxxxxxx> wrote in message

news:1176961801.841343.151310@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Cisco documents mention that the usage of L3 switches for the Campus
network designs result in more efficient bandwidth utilization
compared to using the L2 switches. Can anybody elaborate on why it is
so?

Well, I'm not exactly sure the reference that you are speaking of, but here
are my thoughts...

Many campus networks now have a need for a lot of different vlans and there
is a need to route between the vlans. You can develop an L2 scheme with
everything going back to the core to be routed. However, it would be much
more efficient to have distributed routing at the campus. Given that campus
networks now have high bandwidth usage, this could prove to be an extremely
expensive using routers. However, L3 switches can be much less expensive,
have many more ports and can forward the packets at a higher rate. So, it
only makes sense to deploy a handful of L3 switches instead of routing
everything back to the core or using multiple routers.

Hope that helps,

Jim

I agree with Jim. Distributed layer 3 can be very rewarding, and is
also the latest push from Cisco for campus datacenter networking.
That being said, things get complicated in that distributed layer 3
networks require some GREAT IP/Network planning, as you really need to
focus on summarization. In the core model, you can create large vlans
and trunk them out and slowly fill them up as servers are added. In
the case of distributed layer 3 (or at least true, fully distributed
layer 3), each subnet can only have as many IPs as there are ports.
Not only that, but I'm sure you are going to end up with requirements
for servers, or load balancing, etc, that will require segmentation.
So how do you decide what your model for VLANs are going to be on the
l3 switches?

Perhaps a good medium solution is to roll out Layer 3 to each
building, but still have a set of 'core' switches in each location
that hold your layer 3. This way each building will have layer 3 and
routing relationships, but you don't have to worry about potential
segmentation nightmares. In short, there are 100 ways this stuff can
be done, but it all comes down to your current requirements, your
knowledge/understanding of changing/future requirements, and your
budget. Pushing cores to each building may be costly, but then again
you can use cores as distribution and access layer switches if you
don't have ungodly requirements for bandwidth.

This is why it is hard to find any kind of bible for 'network design',
because there is no single right answer, and just about every business
has vastly different requirements.....there are always exceptions.

.

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