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load balance


   I have a cisco 2801 router and I want to connect two ADSL links on it  and balance the load but not that kind of IOS that team would need or if  I would be useful?




load balance

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Posted by WebUser Chen Sheffer

Cisco Employee

load balance

Hi Marisol,

2801 can load balance between multiple links.

I don't know if your router has a direct DSL interface or not, but you'll be better of terminating the telephone line / DSL line on a regular DSL modem which your ISP provides and is willing to troubleshoot.

Then connect the Ethernet cables between the 2801 ports and the DSL modems.

Keep DSL in bridge mode, and terminate the PPPoE (if your provider has this, it mostly is this way), and use a Dialer Interface as the outside interface.

You will have two default routes , one pointing to each next hop.

You'll have to NAT your inside pool to both public blocks, with route-maps, with match interface.

Please note, load-balancing will not be per packet, but will be per flow (source ip , destination ip pair).

To know which flow will take which path, use:

Router#show ip cef exact-route

Also, load-balancing wouldn't be cummulative due to the above fact.

So , if you have one link with 7 Mbps, and the other with 5 Mbps, don't expect to open a speedtest site and hope to see 7+5=12 Mbps speed. If it takes the 7 Mbps link, thats the max you get, else 5Mbps.

However, will multiple sessions / PCs that will be sending flows, and if they are statistically balanced / random flows, you should see both links being almost equally utilized.

A similar , scenario is discussed here (mainly for the nat config part)

IP Addressing Services

IOS NAT Load-Balancing for Two ISP Connections

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