mpls question

[waldekwaldek5888]

Hello guys,

I have the following questions. Our customer has the plain Cisco IP network (they are using ISRs 2800/2900/ASR1k series and Catalyst 3750x switches). Now they want to migrate to MPLS. All the routers have copper interfaces. The routers are connected to Cat3750x switches (by using copper interfaces on both ends). Cat3750x switches do terminate fiber dwdm links from other geo locations (sfp/sfp+ from mux/demux). The separation here is done by using vlans and L3 subinterfaces on the routers. As you can see WAN links are not terminated directly on the routers. Let's say that now I want to enable mpls in the network (ldp/mp-bgp on the routers etc). Cat3750x would act as plain transit ethernet nodes here. Will that work? Or I need to move WAN links back to the routers so that they would be terminated directly on the routers and not on the switches (and remove Cat3750x entirely)?

[filopeter]

Hello,

since the Cat3750x switches provide only Layer 2 connectivity and all Layer 3 connectivity is done by routers (subinterfaces), you can implement MPLS functionality without changing the existing topology.
Just check if the Cat3750x are capable to handle larger mtu (show system mtu), as MPLS adds 4 bytes per label to forwarded/labelled packet.

Best Regards,

P.

[loris.marcellini]

Hey, sure you can do that. Just keep the trunk (I suppose) between switch and router and just enable MPLS under vlan interfaces/subinterfaces. It's nothing different than terminating physical circuits on the router :)

PS.

Check MTU as you would  probably do regardless of where circuits are terminated.

Hope this helps.

L.

[waldekwaldek5888]

Thank you very much for the answers.