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Multi-router configuration

Posted on 2003-03-24
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Last Modified: 2010-04-17
Hi,

we are getting a new ISP whereby we get 2 E1 links in to our building. both these plug in to the same router and are load balanced (non-BGP). We were wondering if it is possible, without the use of BGP (or just using private BGP routes within our own network), to add a second router to the configuration... plug one line in to each router and have a floating ip address between the 2 on the internal interfaces... but still load balance the 2 lines. obviously this means if one router fails we will loose a link. also if one of the links dies, all traffic should be routed through the router that still has the active line.

please note the pair of routers should be in a spanning tree config with 2 cisco pix
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Question by:wizard2000
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15 Comments
 
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Expert Comment

by:RouterDude
ID: 8198495
I think this would cause more problems than it would resolve. Load balancing would be virtually impossible since one router would not know what the other one is doing as far as packets in/out. Using a Cisco network running CEF, it is possible to load balance without large routing protocols running. One scenario I thought of though would require 3 routers and would only be possible if both E1's are coming from the same ISP off the same router. One router to each E1 using an unnumbered serial interface pointing to the ethernet, then connect both ethernet ports to a single ethernet router to do the load balancing and routing. If you are going to peer off 2 different ISP's you will need to use one router running bgp.
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Expert Comment

by:epylko
ID: 8198527
You could do it, but you would really want to test out failure situations - that could cause problems with the network.

I would use HSRP between the 2 routers for the virtual IP address that the PIX points to and have HSRP track the E1 interface.

After that, on one router I would route all even IP addresses out your local E1 and route all odd IP packets to the other router.  I think this should probably be done via a private ethernet interface between the routers and also with a crossover cable.  That way, if the interface goes down the static route will go away and a floating static (to keep the odd IP packets local) would work.

-Eric
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Author Comment

by:wizard2000
ID: 8198953
routerdude... whats the point in 3 routers in that config? it brings you back to a single point of failure!

lets say we brought bgp in to play... is it possible to have the 2 router config then?
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Expert Comment

by:lrmoore
ID: 8200034
Been there, done that too many times. From experience- your best bet is to keep two lines on the same router and load  balance. With two routers, you cannot load-balance because HSRP is for failover/redundency and not loadbalancing. If you are concerned about the router itself failing, keep a 2nd "cold" spare router configured and ready to power up and manually move the T1 lines over.

Do you have your two PIX FW's in a failover pair? Pix does not do spanning tree, and neither do the routers unless you setup a bridge group, and that is not what you are trying to do.

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Expert Comment

by:pedrow
ID: 8200489
I think you should try and think what's more important. Redundancy or load balancing.

There are different ways to try and balance outbound traffic in hsrp environments.

One method is to have multiple vlans, each with hsrp configured. the hsrp primary router would alternate with each vlan. i.e. odd numbered vlans would have router1 designated as the hsrp primary, router2 pointing to the second. This might be difficult with the pixes(pixen?) as I don't think that they're yet flexible enough to deal with trunked vlans.

Another option which you might want to consider, is use hsrp groups. So, the idea is that you have two hsrp addresses on the same network. So, the ethernet interface of each router would look like this:

router1:
int fa0/0
 ip address 172.16.1.2 255.255.255.0
 standby priority 100 preempt
 standby ip 172.16.1.1
 standby track Serial0/0

 standby 1 priority 95 preempt
 standby 1 ip 172.16.1.4
 standby 1 track Serial0/0

router2:
int fa0/0
 ip address 172.16.1.3 255.255.255.0
 standby priority 95 preempt
 standby ip 172.16.1.1
 standby track Serial0/0

 standby 1 priority 100 preempt
 standby 1 ip 172.16.1.4
 standby 1 track Serial0/0

So, what you could do then is have two default gateways on the same lan, one sending traffic out of router1, the other  out of router2.

In the event of a link/router/interface failure, the second router will assume the burden of all the traffic.

Make sure that if you're not using a dynamic routing protocol(especially!) that you only have the spread of the hsrp priorities less than 10, as the interface command with the 'track' feature will only lower the hsrp priority by 10.

I'm not sure how gracefully pixen handle multiple default routes(lrmoore? can you shed some light on this subject?) and load balancing between them.

Also, don't be afraid of bgp. You don't have to get full tables from your provider...they shouldn't have a problem sending you route-map NULL out and default-originate (so all you get is a dynamic default route). But this would be more for fun in your case than functionality :)

hope this helps.
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Author Comment

by:wizard2000
ID: 8201943
the problem with bgp is the cost of the equipment... the ISP says we need at least a 7200... which we don't believe, but they won't budge
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Expert Comment

by:epylko
ID: 8202712
BGP can run on just about any platform... The question is what kind of BGP feed you are going to get.

If it can be done with just default routes, you could run BGP on a 2500.  But, if you want to get more granular you would need to take a partial or even a full feed.

If that's the case, something like a 3725/3745 might fit the bill or even a 2691.  Those models can take lots of memory and they have decent processors.

You probably don't need BGP though.  Look at my first post.

-Eric
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LVL 3

Expert Comment

by:RouterDude
ID: 8203320
If you look at the very beginning of my statement you will see I said it would cause more problems than it would solve. I have a customer who ran BGP on a 2500 with static routes. You will need a beefier router than a 2500 for peered BGP though, a 3600 would work and you can get them cheap, so getting spares would not be a problem. Just like lrmoore said, been there done that. In any case you will need both lines to meet at one single router in order to utilize the bandwidth evenly, hence the 3 router setup, and yes you will have a single point of failure in any case you try to do. I work for a rather large ISP and even we have a single point of failure where we peer, there really is no way around it, thankfully we have a nice 24x7x4 Cisco support contract that will minimize our down time in case that core router pukes.  
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Expert Comment

by:Dial
ID: 8206200
Bottom line - go with HSRP and deal with the loss in bandwidth.  Most people overestimate their need anyway.  It's simple, easy to manage, and the failover time is great.
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LVL 1

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by:wizard2000
ID: 8284422
I have found GLBP, a new cisco protocol giving exactly the functionality i want... here is the description from cisco:

GLBP protects data traffic from a failed router or circuit, like HSRP or VRRP, while allowing packet load sharing between a group of redundant routers.

I guess this is a very new one, or you guys would have known about it! Cheers for the help anyways.
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by:wizard2000
ID: 8284439
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by:Computer101
ID: 8287558
A request for deletion has been made.  If no response or you feel this is in error, comment.  If no objection, I will delete in three days.

Computer101
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LVL 79

Expert Comment

by:lrmoore
ID: 8288126
How about a PAQ w/refund?
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Expert Comment

by:Computer101
ID: 8296078
Agreed, will handle that

Computer101
E-E Admin
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