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Reduntant lan with load balancing

How to set up reduntant LAN Ring topolog with load balancing for a cisco catalyst 3560 platform.

Tohid Naslpak


You have two easy way for both layer2 & 3 implementation.

you can use spanning tree (rapid-pvst or mst) for layer2. for layer3 you can use any dynamic routing protocol to achieve your goal. certainly there are some other ways but it depends on your purpose and goal.


Dear Mirtoid,

If we implement layer -2 STP. how can we make it as load balancing as it block the alternate route.

STP provides for that.  If you build multiple connections, STP blocks all but one, but keeps the others as alternate paths.

If you use plain old STP, you'll see some lag when a link goes down while spanning-tree converges.

With Rapid STP, the lag is reduced significantly to the point you don't notice it.


Ven Taylor
Ven Taylor

Can you provide more detail on what you need to do?

I believe you may need HSRP, VRRP, or GLBP to provide the "redundancy", but I'd like more info from you.


Ven Taylor

Dear Ven,

There are  8 building which are  interconnect via 1G fiber optic ring. here we need to connect  around 500 IP cams to  a centralised locations by using  Cisco catalyst 3560-X and 4503  switches. As we have 1G back bone ring, what I thing is not sufficient. So I just wanted look at setting up of load balancing in ring topology which leads to connect 1G uplink from bi-direction so enhance possibility of 2G throughput to centralised location. if we implement STP there is only one active connection to its root so there may be chance to choke my Bandwidth. So please suggest me some of good protocol with topology for efficient implementation of this network.

Thanks for your time

Abdul Fathah MK

Aah.. Now I think I understand what you're talking about.

It sounds like you've got a vendor provided optical ring with 1 Gig handoffs.

If you're just using Layer 2 switching, you'll only have a single path.

If you're using Layer 3 routing at each building, you can use EIGRP or any decent routing protocol (EIGRP is easiest to configure and tune).  This is assuming you are using a Layer 3 switch at each handoff.

A Layer 3 routing protocol will provide you with use of both rings simultaneously, assuming you have them in separate subnets.

One more thing.

If you "think" its insufficient, I wouldn't spend the money on a second gig handoff.  You should be able to PROVE it.

What is your load at the gig handoffs?  (A show interface will tell you)


Ven Taylor

Dear Ven,

nice ...Could you please elaborate with an example how can we set up layer 3 routing protocol in switching enviornment here we are having 500 hosts from 8 buliding interconnected via Fiber optic ring to centralised location. and using Cisco catalyst 3560-X series with IP Base Image. whether layer3 protocol supported by IP base image or not ?. and what enhance we should make it to work.

we need to make all location  in a different subnet or not ?

Thanks for your time


Assuming your router, using ip base, can support eigrp (I didn't look that up, but you should), here's a drawing and configuration example:

If you have 8 buildings, this will work.  If you have 8 buildings plus a central data center, just give the data center the .1 address.

Here's the config I use for the same type of ring connectivity:

Interface Gig0/0/0

description Ring1

ip address

delay 7


Interface Gig0/0/1

description Ring2

ip address

delay 7


Interface vlan15

description Local Lan subnet

ip address (whatever)


router eigrp 90


##make sure you add your local lan subnet if it's something other than 10.x.x.x

no auto-summary

no passive-interface default


The delay 7 on the ring interfaces will keep your local lans from traversing the ring for local connectivity inside the building.

Hope this makes sense!


Ven Taylor
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How to set up reduntant LAN Ring topolog with load balancing for a cisco catalyst 3560 platform.

For L2, if you can split your hosts into at least two VLANs, PVST or MST would allow load balancing for the separate VLANs while still supporting redundancy.

I f you have the 3560 Ip Base image, i recommend to Implement EIGRP. For the core implement a full EIGRP As and for each building EIGRP Stub network.

For load balance, it is necessary to know wich switch and its way of connection are you using in the Central Building, with this number of end devices i strongly recommend you, at least, a single Catalyst 6500 Chasis with two  720 VSS Supervisor and redudancy components (Power supplies and line cards) or if there is economical contraints deploy a single chasis with redundancy elements.

Now if you have separate switches witch separate IP Addresses you wont be able to configure an etherchannel or load load balance betwen the building and the central one. At least you need a pair of Catalyst 3750x series stacked or any of the 2 situations that i suggest you previously.