Load Sharing When Multihomed to Two ISPs Through Multiple Local Routers

Unanswered Question
Jun 27th, 2008

I have 2*/23 real IP ranges configured on my multiple routers

rtr1 has IP address rtr2 has IP address the other /23 is logical and pointed towards the firewall IP I wish to achieve load sharing for outbound traffic. I am learning only default routes from the ISP. I want 1*/23 to travel via ISP1 and the second /23 to be on ISP2. Inbound would be achieved by As-prepend. I am not sure how to go abt outbound load sharing.

I have referred http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800945bf.shtml but according to it the preferred default path is always ISP-A

can i achieve source based outbound load sharing?


I have this problem too.
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Giuseppe Larosa Sun, 06/29/2008 - 10:53

Hello Sai,

>> can i achieve source based outbound load sharing?

you can achieve it if you use HSRP and make router1 HSRP active for subnet 1, router2 HSRP active for subnet 2. Note: you need to use two different HSRP groups one for each subnet (but this how HSRP works)

I would suggest to track the state of the wan interface on each router on both HSRP groups.

In the document that you have linked there is a case for two ISPs and multiple routers.

However, using default settings each router should prefer the default route received in the eBGP session.

If you are receving only default routes you can even skip the iBGP session between your two routers and use tracking of interface with HSRP as explained before.

hope to help


saimbt Sun, 06/29/2008 - 21:23

Hello Giuseppe,

Creating 2 HSRP groups would attract 2 ethernet ports on the routers and 2 ports on the firewall as well.

I will try this config and get back.


Jacob Samuel Mon, 06/30/2008 - 06:25

dear friend,

that is for traffic originating from LAN right? how can we acheive if we have a Web Portal inside our internal network and ppl have access over this.

And how can we dedicate a particular bandwidth for this source from our total line speed ? also redundnacy, only one isp?




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