Question for the load balancing

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Apr 23rd, 2008
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I begin to work with router Cisco and I am a little lost.

In my compagny we have two WAN lines.

The first has a static IP. The second not.

the two lines are connected in a router cisco, which is connected to the LAN.

You can see it on the picture here :

I must implement a solution of load-balancing of theses two lines.

The traffic is active in the two lines but the charge must be equal between the 2 lines.

I have seen solutions : GLBP, OSPF, CEF, PLS, static routes. But i don't know if they are good for my requirements.

Can you help me, explain me, which solution could be the better one.

Excuse me for my english...

Thank you for your response.

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666Maverick Wed, 04/23/2008 - 23:22
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I can't use BGP, because I can configure only my router (2811). I don't know what is the router of the ISP... And they can't implement BGP (I phoned them). I must find an other solution.

I have thinked on the GLBP protocol, but I don't have two router for this solution.

Do you have an other solution?

Edison Ortiz Thu, 04/24/2008 - 03:49
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GLBP solution is when you have 2 routers at your location and their LAN interfaces are facing your subnet and you want to load-balance the incoming traffic toward their LAN interfaces.

Per your diagram, you only have one router so you can't use GLBP.

One way of 'load-sharing' not 'load-balancing' your internet connection is to break your network in half. One half can be directed to one ISP for internet and the other half to the other ISP.

However, with this approach you would have to use PBR (Policy Based Routing) to perform source-based routing and next-hop redirection as well as multiple NAT entries. It's not the cleanest solution out there.



Sushil Kumar Katre Thu, 04/24/2008 - 03:59
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A potential drawback of this approach is that when one of the link fails that particualr group will loose the connectivity and can not fallback to the active link.

666Maverick Thu, 04/24/2008 - 04:56
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My problem is I have traffic on the two connections. I must have load balancing (or load-sharing, I think it is the same ting). The traffic must be equal between the two connections and if i loose a line, the traffic is routed to the line, which is up).

I must use PBR for have this?

It's the only one solution?

At the moment, I don't know how I can do/implement this solution. I wiil search configuration examples, or search how it function.

Thank you for your help and for your response if I haven't very good understood. :)

Sushil Kumar Katre Thu, 04/24/2008 - 05:01
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Why don't you add another small router capable of doing NAT and terminate second internet link on that. This would resolve all your issues.

What kind of Internet connection do you have? Are you getting any DSL connectivity?

-> Sushil

Sushil Kumar Katre Thu, 04/24/2008 - 06:46
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Here's my suggestion.

You have ADSL connectivity. Ask one of the providers to give you the ADSL router and terminate it on the ethernet interface of 2811 router. Terminate the second link directly on the ADSL interface of the router.

Configure two default routes on the 2811 router with same AD. This will distribute the traffic on both the links. Configure NAT on 2811 router and ADSL router. Configure SAA probe to check the availability of the ADSL link terminated on ADSL router and associate it with the default route pointing to the ADSL router. If the SAA object goes down that specific route would be removed from the routing table, all the traffic would be forwarded to the ADSL link directly terminated on 2811 router. If the ADSL link directly terminated on 2811 router fails the route would be taken out automatically and all traffic would be forwarded to ADSL router.

You achieve load balancing and failover using this.

This is the only viable option I see apart from BGP.

-> Sushil

Sushil Kumar Katre Thu, 04/24/2008 - 03:06
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You either need to implement BGP or terminate one of the links on another router. Each router would have an internet connectivity and individual NAT table. Use PBR to redirect the traffic.

If you have got ADSL connectivity and using ADSL router you can implement NAT on that router.

-> Sushil

lamav Thu, 04/24/2008 - 07:56
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"In order to load-share an internet connection, you must use BGP and have the ISPs announce your /24 block out to the internet."

Edison, why would configuring 2 equal cost default routes, each pointing to one of the ISPs, not work?

ip route ISP A-next hop

ip route ISP B-next hop


Edison Ortiz Fri, 04/25/2008 - 19:08
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What IP subnet is being advertised to each ISP?

If you are planning to use the IP subnet assigned from each ISP, you must take NAT into account and as far as I know, you can't load-balance nor load-share with NAT, unless you break the source network into blocks with a ACL+route-map.

Now, if you are NAT'ng into your own public /24 subnet, you can advertised this block to both ISPs and load-share the connection.


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