Categories: Cisco

How to configure load balancing between two ISP connections using route-maps on Cisco routers.

Assuming you have a dual ISP connection to the internet, the best thing
may not be automatic fail-over. Instead of having one ISP connection lying
there, just waiting for the primary link to fail, you can configure load
balancing to have some of your traffics go through that link. This will help
speed up your connections and avoid congesting your primary link. To do this, I
am going to use route-maps and ACLs. It is very easy and straight forward.
Let’s do it.

For this test, I have a Cisco router with the following details:
f0/0 connects to ISP1 on IP
f0/1 connects to ISP2 on IP
f1/0 connects to the LAN on IP
We have two hosts on the LAN. Host A has IP while host B
has IP
Objective: my objective is to load balance across the two ISP links such
that host A internet-bound traffics will go through ISP1 while those of host B
will go through ISP2
On my router, I will do the followings:
>> Create an access-list to match host A’s IP address (to be
called ISP1-Users)
>> Create an access-list to match host B’s IP address (to be
called ISP2-Users)
>> Create a route-map to match host A’s traffics and set his
gateway to ISP1
>> Create a route-map to match host B’s traffics and set his
gateway to ISP2
I will use a named extended access-list. This will make it easy to add
more IP addresses depending on how many hosts you want to give internet access
through ISP1 or ISP2 as the case may be.
access-list extended ISP1-Users
ip host any
access-list extended ISP2-Users
ip host any
Next, we create a route-map
ip add ISP1-Users
ip next
ip next-hop
ip add ISP2-Users
ip next-hop
The two IP addresses referenced in the route-map statements are the two
ISP gateways. is the gateway to ISP1 while is the
gateway to ISP2. The disadvantage to this kind of setup is that hostA will remain down when ISP1 goes down even though ISP2 is up. The setup can be updated to allow hostA switch switch to ISP2 whenever ISP1 is observed down. I will be sharing this in a different setup. Thanks for reading and remain safe.

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