L2 & L3 Link Configuration

[nabeelcse07]

I am working on a scenario where I have Cisco IE3400 Series Switch with Network Advantage License. Our client requirement is to have 2 x Uplinks one is directly connected over fiber with a remote switch (to be configured as L3 using EIGRP) and other uplink connected to L2 Switch (to be configured as L2 Link). My concern is regarding Traffic Flow in this scenario? Which Link will act as primary and which one will act as secondary.

Regards,

NA

[rasmus.elmholt]

This seems like a normal Spanning Tree issue, the link towards the Root bridge will be active and forwarding, and the link with a longer path(link speed included) will be designated and not forwarding traffic until the primary one goes down.

But if you are configuring one link as a L3 link with EIGPR and the other link as a L2 link, with EIGRP over the SVI, then we have the routing metric to select the active path, and the standby(or ECMP)

[nabeelcse07]

HI Rasmus,

Thank you for your response.

Actually first link from ICT Switch L3 Link will be over Fiber Optic Cable and Other Link is connected to a aggregate switch which is connected to a DMR device. requirement is to have FO link as primary and Microwave link as backup. I am more concerned about the Link between ICT Switch and Aggregate Link? DO I need to configure this as L3 also?

[rasmus.elmholt]

will this be a routed handoff? On a L3 link over FO, and a L2 link over the DMR device?

Let me ask in another way, is both links connected to the same L2 domain?

If you already have this configured, please share some configuration of the links and routing, and it is easier to visualize the setup.

[nabeelcse07]

Its not configured yet. Still in design phase. Customer Requirement is to L3 routing protocol to be used via FO and Microwave Link. I have attached here the Setup for your reference to have better understanding.  What are your recommendations does the link between Switch - 1 & Aggregate needs to be L2 or L3?

[rasmus.elmholt]

If possible always make L3 links, it will save you some STP headache. And then tune the active/active or active/backup using you routing protocol metrics.

That would be my suggestion, but there are many ways to accomplish the same task.

[pieterh]

the switch will use NO primary/ secondary relationship using a L2 and L3 link!

a host in the same L2 network may prefer the L2 link if the destination address in on the same network (L2 = based on MAC-address)

the same host may use the L3 link if the data needs to be routed to another subnet reachable from the L3 link (L3 = routed -> mostly using  tcp/ip address)