"Routed" port vs SVI - differences?

[darren.g]

Learned ones! :-)

I have a multi-site network which is shortly, thankfully, to become much faster with the implementation of some dark fibre running at a minimum of 1 gig (10 if I can convince the pwoers-that-be to splash out for the requesit optics and interfaces).

Currently, the network is based around a provider MPLS network and all links are routed - interfaces, even on switches, have an IP address when associated with a link (no switchport, ip address <blah> etc), which I want to change.

(Apologies for the crappy drawing)

What I want to do is use the dark fibre links as trunks, and assign SVI's at the end points (rather than a routed IP in the middle). So from the core to site 2 would be one VLAN, trunked through site 1, to site 3 another VLAN trunked through site 1 - this is applicable for more sites than listed, but you should get the general idea.

What I'm curious about is if there is any advantage to doing this over having the link from core to site 1 routed (no switchport at each end), then site 1 to site 2 routed, site 1 to site 3 routed and so on, and running routing on the switch (3750X with ipbase, core is 3750X with ipservices).

Is there a performance issue likely, or some gotcha I'm not aware of in running trunks/SVI's like this? To be honest, I never even considered there might be until the other day when I was discussing it with my boss and he asked which one was more advantageous from a performance/reliability point of view.

Interested in any comments either for or against.

Cheers

[Joseph W. Doherty · Accepted solution]

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Posting

L2, per hop forwarding, generally isn't much faster then L3, per hop forwarding, on L3 switches.

The adage "switch when you can, route when you must", doesn't really apply when using L3 switches.

Considering the other advantages of routing, I would suggest continuing the more usual practice of "routing in the middle".

[Richard Burts · Accepted solution]

The suggestion by the original poster to run VLANs and configure SVIs will result in running Spanning Tree everywhere. So now a BPDU from the core will transit site 1 to get to site 2. I see that as a disadvantage

Also when something is not working with access to site 3 you now will have to consider the possibilities that there might be a problem with the VLAN on the core, or there might be a problem with the VLAN at site 1 or there might be a problem with the VLAN at site 3. It seems to me that troubleshooting is much easier if you can localize the problem by routing on the links between sites.

HTH

Rick

[sansarav720e · Accepted solution]

Dear Darren ,

               I assume all your SITE A , B , C is running with layer 3 3750 switch , if you want to have multiple network segment on each site in future like 192.168.1.0/24 & 192.168.2.0/24 you need to go for routed port .

     If you have got layer 2 switch on your site 2 & site 3 u can have either access port or trunk port based on VLAN avilable on each site

            If want to have same network range on your both site 2 & site 3 then u need to configured Single SVI on your site 1 switch and you need to pass through same vlan on switch port connecting to site 2 & site 3 .

      L3 switching is more faster than L2 trunk port , where  L2 has got BPDU packet passing through interface for every 2 seconds & VTP packets (when u configured as trunk port) ..

HTH

Thanks

Santhosh Sarav

[darren.g]

Thanks for your input gents - more to think about. I might have to redesign my new design already. :-)

Cheers.