Jon,

Thanks for the reply. At the moment, I'm looking at the best implementation for switching core and one of the options is STP, while another is some of the link-state routing protocols (all switches are L3 capable).

Can tou advise on pros/cons for both of these?

Thanks,

Marko

Marko,

One of the design i did recently, i used 2 6500's as core switches connected via L3 and L2 (trunks) to the access layer switches Cat 3750. The Design was based on Core/Access layer no distribution. On the access layer, No VLAN's spanning across multiple access layer switches so no need for STP between the access/core layer and no STP between the cores since i used layer 3. Traffic between the vlans is routed via the core switches. With my design, i have no concern for STP convergence. The recommended design for hierarchical layer is if you can do without STP, then don't use it if you don't have any requirements for it. I have worked in environments where they are routing on the access layer using EIGRP instead of using STP.

see this doc for better explanation including pros/cons when using STP or Dynamic routing.

http://www.cisco.com/application/pdf/en/us/guest/netsol/ns431/c649/ccmigration_09186a008093b876.pdf

Francisco

One major difference is, STP blocks all but one path, routing leaves them open, and depending on protocol and topology, might use multiple paths. Another difference is speed of convergence, which could be epecially slow with the original STP, but later variants are usually much faster.

Modern designs tend to recommend L3, since modern L3 switches are usually nearly as fast as L2 switches.

Thank you all for replies, much appreciated.

Since L3 is recommended in the core, would you recommend MPLS as layer 2.5 with OSPF as the best choice?

Regards,

Marko

I haven't worked with LAN MPLS. However, seems a big jump from from either a typical LAN's L2 or L3 unless you really need multiple VRFs within your LAN. Perhaps other posters might comment on using MPLS within a LAN.

Marko

I agree with Joseph. MPLS in a LAN environment is not necessarily wrong but it really does depend on your requirements. If you have a need to completely separate different end user traffic with separate routing tables etc. or perhaps you have overlapping addressing problems then just maybe MPLS could be used but in an ethernet LAN for an Enterprise it would be a difficult one to justify.

Jon

I'm with Jon and Joseph. I really believe in KISS (Keep it Simple...)

MPLS is almost certainly OTT for a lan environment, unless the LAN environment is a multi client shared infrastructure datacentre!

Keep it simple, ad when it breaks at 3AM on sunday morning, and whoever is on shift can sort it. Make a complex solution and what is gonna happen? Yup - you get the call.

As for L2 Vs L3 - with L3 switching being commonplace there is no performance benefit in an L2 solution. L2 will only allow a single path to be active, where L3 can permit multiple paths to be active, and is less prone to things like undrectional link errors. If you were to use something like OSPF with BFD, you could probably knock spots of the STP convergence time as well.