Internet Load Balancing and Failover

Unanswered Question
Jul 21st, 2009

Dear All,

I have to implement a senerio in my office. the points below explain the requirment.

1. We have two ISPs, each link is 3Mbps

2. We have one Internet router with four Fastethernet Ports

3. We have to connect links from both the ISPs and use both the links for load balancing and failover.

4. attached is the ppt, which could explain in more detail.

Please help with the concept and configuration.

I have this problem too.
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vishwancc Tue, 07/21/2009 - 06:27


Will you be running a routing protocol with the ISP or using static routes.

static load balancing, you can configure traffic load balancing on a per-packet basis without using a dynamic routing protocol.

Most routers will perform load balancing automatically if several equal cost paths to a destination exist on multiple interfaces.

Cisco routers perform load balancing on a per-destination, per-source-destination and per-packet basis. Load can be balanced across up to six equal cost paths.

ip route x.x.x.x y.y.y.y e0

If you are using a routing protocol please let me know which protocol are you using.



engineer_msu Tue, 07/21/2009 - 08:13

Dear Chao,

I will use static routing.

Please let me know the configuration for this.

Rick Morris Tue, 07/21/2009 - 10:54

for what you are saying your routes will look like this:

ip route FastEthernet0/0

ip route FastEthernet0/1

chinkevi_2 Tue, 07/21/2009 - 20:41

right, even though outgoing traffic is load balanced there is no way to guarantee return traffic is doing the same.

vishwancc Wed, 07/22/2009 - 06:27

Hi Chink,

Good point raised here ,but this is what i think will happen.

If the packet will go to internet using ISP 1 public ip it will not come back through ISP 2 path but only ISP 1 path and viceversa,since different ISP.

So packet transferred through ISP1 will come back through the same link.

The only difference will be the delay provided the ISP to access internet.

This is what my understanding is.



k.hariharan1 Tue, 07/21/2009 - 20:51


let me know what type of link you are getting from service provider.

1.copper link (serial termination)


2. Fiber link (Ethernet delivery)

if its fiber Ethernet delivery, you need to add few more command in order to achieve automatic failover

bcoz ethernet interface will never put down its carrier signal.


Hariharan k

engineer_msu Tue, 07/21/2009 - 22:14


One is wireless link and the otherone is fiber link, both the links will be connected to the ethernet ports of the router.

k.hariharan1 Tue, 07/21/2009 - 22:27


here is the sample configuration for you.

Hope this will help you

IP sla monitor 1

type echo protocol ipIcmpEcho your_first_test_ip source-ipaddr your_source_ip

timeout 2000

threshold 2000

frequency 3

IP sla monitor schedule 1 life forever start-time now

track 100 rtr 1 reachability

delay down 10 up 20

IP sla monitor 2

type echo protocol ipIcmpEcho your_second_test_ip source-ipaddr your_source_ip

timeout 2000

threshold 2000

frequency 3

IP sla monitor schedule 2 life forever start-time now

track 200 rtr 1 reachability

delay down 10 up 20

IP route x.x.x.x track 100

IP route x.x.x.x track 200

if you are using Nating

ip nat inside source route-map ISPA interface FastEthernet0/1 overload

ip nat inside source route-map ISPB interface FastEthernet0/0 overload

access-list 110 permit ip any

route-map ISPA permit 10

match ip address 110

match interface FastEthernet0/1


route-map ISPB permit 10

match ip address 110

match interface FastEthernet0/0


Hariharan k


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