Hi, I dont think you answered any of my concerns. But I appreciate your time.

Anyone else?

Edison:

Thats just my point: There are no L3 connections shown -- at all. And I cant read this guys mind and nor can the client, so we have no way of knowing what hes thinking. All we have to go on is the diagram that he has provided.

There should be routed connections between each of the distribution switches as well as between the core switches.

The distribution switches should also be dual-homed to the core switches with ROUTED connections, not L2 trunks. Why extend the switched environment all the way up to the core?? There should be no L2 connections linking the distribution and core switches. This would create a huge L2-loop/STP domain. There is no L3 isolation.

All this is basic but it is not shown. That is why I say it violates basic design principles.

No??

If this is the final draft (not a work in progress) then this drawing does not meet any design guideline.

Not only the Layer3 design is missing but the L2 allocation as well. Is he planning to run everything on Vlan1 ?

I want to give the benefit of the doubt, this person must have another drawing with more information.

Edison:

The purpose of this diagram was to show the general architecture and design, not specific configurations. So, the fact that there are no VLANs shown or what mode of STP is is going to be running is OK. We know they will be there in the future.

This diagram was to show switch hardware, modules, and the connections between them.

My problem is not just with what he does NOT show, but what he DOES show, like L2 trunks between the distribution and core layers. That is just so dead wrong. So, another drawing lurking somewhere does not solve the problem.

I don't understand how can it be dead wrong. If you had 6500s running in hybrid mode, that's how switches would interconnect (L2 trunks).

Many companies even when using Native IOS, still implement L2 inter-switch links, because that's the design they are used to. BTW, I'm referring to large companies, not just small shops.

Hi Victor

I agree with Edison on this. There is nothing inherently "wrong" with this design as such although without more informtion it is difficult to say exactly what is being proposed.

The L2 40Gbps channel between the distribution switches leads me to believe that the L3 vlan interfaces for the server vlans will be on the distribution switches. Now if you want to run HSRP between the 2 distro switches then you need a L2 channel between your distro switches unless you want HSRP to traverse the access-layer.

As for L2 to the core, well Cisco have changed design recommendations a few times on this. It did used to be switch in the core for speed although with the advent of L3 switches that does not hold as true. But to say it is "dead wrong" may be overstating it a bit :). It would be helpful to question his choice on L2 but there may be very good reasons why.

It's also not clear from the visio what the data centre core consists of and what else is attached into it. I would investigate the possbility of using L3 links to the core which would allow automatic load-balancing across the uplinks and would constrain STP to the distro/access layers.

Dominic also makes a valid point in that having the access-layer connected to the distro layer with L2 links allows for future use of service modules in the distro switches.

Jon

Thanks guys...

IMHO, I think that extending the switched environement up to the core is absolutely preposterous these days. Forgive me for being so uncompromising about this. A switched core was the recommendation years ago, before the advent of CEF and dCEF. Switching was faster than routing, but not anymore.

In fact, the trend now is to mitigate and minimize the switched environment even further by deploying EIGRP or OSPF at the access layer (L3 isolation) to create a routed access layer.

Therefore, linking the distribution layer with the core using L2 trunks to me is completely senseless and dangerous. An L2 loop can wipe out the entire data center, as opposed to just isolating the outage to the the access layer.

As for the L2 trunks between distro switch 1 and 2, of course that makes perfect sense. They must exist. My problem was not that they exist, it was that the routed connections between distro 1 and 2 do not exist. That is a basic requirement.

As for the L2 connections between core 1 and 2, they should not exist.

I think this is a good discussion...

Thanks

Victor,

When creating a network design, the number one goal is meeting customer's needs and requirement.

We don't know this customer's requirement so stating that is dead wrong, can be a bit dangerous.

I agree, I don't see how this violates the design principles. While, the drawing does not mention any L3 Vlans, it is very likely the distribution and core switches will have plenty of them.

I believe that another diagram should be provided with an explains how the routing is going to take place.

Give him the benefit to explain this design in more detail.

Hi, Sal:

Please read my last post (2 up from yours).