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Load Balance Internet Multiple ISPs

Hi Guys,

Just wondering what you're doing to load balanace internet traffic?  I'm interested in load balancing internet traffic (outbound -AND- INBOUND) using multiple (at least 2) ISPs.  Some of the methods I have used in the past have certain weaknesses.. basic DNS load balancer (relies on multiple IP addresses per host), OER/PFR (ability to control INbound is limited unless complex configuration and coopearation with ISPs)...  This is kind of a broad open ended question.. It seems like something that would be a common issue and am wondering what other are doing with the capabilities 2800, 2900, 3800, 3900 series routers...  Thanks!

Cisco Employee

Hi Bart,

I haven't set this up myself however I have the following document has information on load balancing between two ISPs.

Maybe someone who has set this up before can provide more information.




Thanks.  I was hoping to find others who are using this in the real world.  Your example does not cover the topic of load balancing INBOUND traffic.  Balancing the Outbound is less difficult..  Anyone else out there?


For load balancing if you have EBGP to your both upstreams , you can send  you can send prefixA  through ISP A and prefixB through ISP B .

Prefix ISP_A inbound will be through ISP_A and Prefix ISP_B thugh ISP_B

route-map ISP_A permit 10
match ip address prefix-list ISP_A

route-map ISP_A permit 20
match ip address prefix-list ISP_B
set as-path prepend 1234 1234 1234 1234

route-map ISP_B permit 10
match ip address prefix-list ISP_B

route-map ISP_B permit 20
match ip address prefix-list ISP_A

set as-path prepend 1234 1234 1234 1234

router bgp 1234
neighbor ISP_A route-map ISP_A out
neighbor ISP_B route-map ISP_B out

Like this you can balance your traffic based on your prefix




Hello Burt,

if you have at least two public blocks /24 you can use the configuration suggested by Haris by using selective AS path prepending.

But this requires ISPs to accept AS path prepended advertisements without attempting to summarize the routes.

So this may require some arrangements with ISPA and ISPB people.

Also you cannot expect a 50% ratio in traffic, getting some traffic back from both ISPs can be seen as a good result.

This is because one ISP can have a better connectivity to the internet towards destinations of interest. Those destinations may send traffic back to ISPA for example even if a prepended path is involved for multiple reasons like they are customers of ISPA, their ISPs have peering agreements with ISPA and not with ISPB and so on.

Hope to help




It is a typical case. You have multiple ways of achieving outbound load balancing like Dynamic routing protocols/Static default route tricks with traffic ratio/OER

But INBOUND is a challenge with default IOS capability. AFAIK, Either you can use BGP load sharing in aggrement with you ISP or you have to use Load Balancer appliance like Radware linkproof or F5 which uses Authorative DNS concept




I know this is an old post, I was looking for something like this a year ago and we ended up buying fat pipe which handles our 3 ISP providers inbound/outbound this is also our authorataitve DNS without the need on doing any extra work with your ISP providers. We have it for a year now and so far we are impress with its capabilities and very simple to setup.



I am doing this project at the moment and have similar issues.  Outbound is fine.  I am using HSRP with route maps.  Inbound though i dont know where to start.

I have two internet pipes with NAT ip address pools on both.  The issue is if a NAT an external dmz server coming in from ourside how can i get it to failover to the other internet pipe because i cant take the nat address with me

Have you any advice for me.  It would be really appreciated.

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