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Design Question for Cisco Redundant Routers

Posted on 2008-10-29
Last Modified: 2012-06-21
We have purchased a second point to point T1 between our central offices and all outer offices from a different carrier coming into a different part of our building, etc for redundancy.  We want to also have a second router these T1's terminate into in our central office and need help with suggestiosn on design.

In our central office we'll now have two rotuers (Router A and Router B).  Our outer on the other side will be a single router (Router A).  For the sake of simplicity I'm going to list one office and not all our differnet variations with other outer offices.

We'll have 3 T1s from one carrier going from Router A in the central office to Router A in the outer office.  Then we'll have 1 more T1 (from a seperate carrier) going from Router B in the central office to Router A in the outer office.  The point is, 2 routers in central office terminate to 1 router in outer office.

The goal is to have all these links "hot" and load balanced plus failover if one link or carrier goes down.  

Other Details:
1.  These are all Point to Point links (currenlty we use a multilink setup), no MPLS
2.  Some of the links are fractional so they carry voice as well as data.

Please let me know what other info I can provide, we are just looking for advice from anyone who has implemented a similiar setup and what they needed to purchase along with what routing protocols they used.

Question by:microIT
  • 6
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LVL 50

Expert Comment

by:Don Johnston
ID: 22833010
All you need is a decent routing protocol. OSPF or EIGRP (if you've got Cisco equipment) will work fine for this purpose.

Author Comment

ID: 22835757
I'm not sure that is all we need for the load balancing.  I'm not sure if one of EIGRP metrics is congestion.  I think it picks the best route based on Bandwidth the route has so it would ALWAYS pick the 3 T1's from our primary carrier unless they were down.  In a perfect scenario it would balance the traffic across all 4 T1's (like a multilink does, except you can't use multilink setup between two routers).  Remember there is only dual routers on one end of the link too.

I have the EIGRP recommendation although I'm not sure it gets us true Load Balancing.  I also have been told to use GLBP (Gateway Load Balancing Protocol) on the central end with two routers and HSRP (Hot Standby Routing Protocol) on the outer end with one router.  I'm not sure if that solution works, haven't done enough reading on those two protocols.
LVL 50

Expert Comment

by:Don Johnston
ID: 22836158
By default, EIGRP uses bandwidth AND delay. It can also be configured to consider load and reliability.

GLBP and HSRP perform completely different functions than routing protocols. The purpose of HSRP is to provide fault tolerant default-gateway serivces. GLBP does the same thing as HSRP but add load balancing.

So the question is, do you want redundancy and load balancing of the router-to-router links, redundany and load balancing of the default-gateway or both?
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Author Comment

ID: 22837651
Thank you Don for your reply first of all.  I'll try to explain the best I can of what we are attempting to accomplish.

We want redundancy at our central location, so two routers.  We want the links to load balance accross these two routers so redundancy (failover) from the two routers and load balancing is the goal.

Now the outer office is different it will only have one router.  So at those locations we'll want load balancing and obviously if a link is down it should still be able to failover to the other three for instance.

Does that make sense?  Let me know.
LVL 50

Expert Comment

by:Don Johnston
ID: 22839486
At the location with two routers, you'll need a routing protocol (OSPF or EIGRP) and GLBP. At the location with one router you will only need a routing protocol.

Author Comment

ID: 22840873
Ok, that makes sense and I'll look into that more.  Do you have any sample config files you are willing to share using EIGRP and/or GLBP?  A visual would be nice.
LVL 50

Accepted Solution

Don Johnston earned 500 total points
ID: 22843655
Bear in mind that GLBP is not supported on all IOS versions. If your platform doesn't support it, you may have to use HSRP instead.

glbp 1
glbp 1 priority 105
glbp 1 preempt
router eigrp 1

Open in new window


Author Comment

ID: 22847332
Thank you Don.  To build on that I have another question related to EIGRP.  Our central location router has a static route, i can't find where is used anywhere and EIGRP is also configured on this router.  Does the static route take precedence, it doesn't appear so as EIGRP is still picking the proper route for that subnet but wanted to ask?  I took over on this config thus the confusion, I didn't apply it.  Is there a good command to see if I can remove this static route, it has to be old, can't find any neighboring interface using that 192 address.
LVL 50

Expert Comment

by:Don Johnston
ID: 22848780
If you have a valid static route and an EIGRP route to the same network, the static route will be preferred as it has a lower administrative distance. It sounds like the static route may be invalid as it has a bad next hop address. If that's the case then there shouldn't be any problem removing it.
LVL 50

Expert Comment

by:Don Johnston
ID: 22866255
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