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Redundancy link - Fiber & Microwave


We have an existing fiber link from 2 sites: Exchange 1 <---> Exchange 2

We would like to engage a contractor to supply us a secondary/redundant Microwave link; linking both sites.

If we have a single 2900 Series router at both sites.

Question is: what is the best method to provide redundancy OR load sharing for both fiber & microwave link?

Have not dealt with microwave link before; is there any special config that is needed on Cisco 2900 router side?

From my understanding; microwave vendor will be giving us a copper/RJ45 connection to our cisco 2900 router.

Please advise.

Collin Clark

No special config needed. I have a customer than runs microwave. We also get an RJ-45 handoff so the whole thing is pretty transparent to us. We set it up more in an active/passive scenario. We have to L3 connections between the sites and adjusted the AD of the IGP so the dark fiber was preferred.

Hope it helps.

Dear Concern,


We have two sites  A ------B both side has cisco l3 switch we make primary link with fiber

and backup with microwave would you please help me in this regard this is l2 link

Dear asadjawed


I'm curious to know what was your solution for that ?

i have the Same topology (microwave main and fiber backup) between two sites

Both sides have L2 switch


what's the best way to have redundancy ?


Best regards

You have used a very old post to ask your question. You might have more/better responses if you had started a new discussion. But you asked your question here and I have these responses:

- if you have 2 connections, one microwave and one fiber, why would microwave be main? I would think that fiber would be preferred over microwave?

= if this is limited to L2 then Spanning Tree would detect 2 paths between sites and put one into blocking mode. If the chosen path becomes unavailable then the alternate path would become active.

- I believe that redundancy would be easier if you treated the site to site links as L3.



Thanks richards for your answer , i appreciate it .


we privilege the Microwave cause we got a lot of cables cut issues in this kind of sites.

Have you encountered any problems with L2 link redundancy that made you believe that L3 is better for redundancy?



Thanks for the explanation. I can see that concern about cable cuts would be a reason to prefer microwave.

In general I prefer layer 3 redundancy because we have more and bette tools and more flexibility for managing the redundancy. L3 has routing protocols, administrative distance, HSRP, route tracking, ability to use different media for redundant paths, ability to prioritize certain types of traffic, where L2 depends of Spanning Tree.



how could i make primary fiber path and secondary microwaves between two l3 switches


The mikrowave link provides a Layer 2 ethernet connection. A simple way to do the failover is using the spanning tree protocol of the switches where the fiber and the microwave links are connected. The bandwidth settings on the switch ports would be used to calculate the best path. It is necessary to change the bandwidth setting on the switch port in order to obtain the desired result.

It is possible also to do load balance with the MST protocol or by changing the port priority of the switch port on a particular vlan.

Marwan ALshawi

i would recommend you to use L3 /30 p2p per link rather than L2 to avoid extending spanning tree and increasing the complexity unless L2 is required between the sites

using IGP or static routes with differnt administrative distance AD as Collin mentioned is the simplest way you can use

also you can use IP SLA to improve the static route and make it more network aware

hope this help

I guess it depends on the requierements. Agree on L3 is effective by using routing different routing protocols and IP SLA. But if a requirement is to transport VLANS on a redundand environmet the network design changes.

Another protocol worth to take a look is UDLD


Thanks for all the input.

If we would like to do Redundancy AND Load balance.

Scenario: where load balancing is in place; if one of the two link is down, it will proceed to route to the active link. & when the dead link comes up it will resume its load balancing task.

Will the below method work?

  1. If i proceed to use 2 static routes with same AD =load balance
  2. And also Use ip sla tracking=failover

Will this achieve my objective?

You have a couple of options. If both links are the same speed you could put them in a layer port channel. That would give you both LB and redundancy. Since it's doubtful that both links are the same speed you can create two L3 links and use IGP to determine LB and redundancy. You will have to tweak the AD on one of the links so they "look" like the same speed. If you're using EIGRP you can use variance.

I woild have done as collin said

"Everybody is genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is a stupid."

just to add to collin's post 5+

if you decide to go with static route i highly recommend you to use it with IP SLA to make sure smooth and quick failover and make it more topology aware routing