Multiple ADSL Links in Active Mode

Unanswered Question
May 18th, 2009


We have 2 Internet Routers with 2 ADSL Ports on individual routers.

Attached n/w diagram will give you an idea of the setup.

The requirement is: all the time 4 ADSL to be used for Internet accessing purpose.

ASA is in single-context mode. On Core switch OSPF is running.

Can someone suggest the necesary changes to be done at gateway level??

I have this problem too.
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Giuseppe Larosa Mon, 05/18/2009 - 12:57

Hello Partha,

routing is not difficult:

ASA can use two default static routes pointing to two HSRP VIPs

R1 will be HSRP Active for VIP1

R2 will be HSRP Active for VIP2

Each R1,2 has two default routes using the two DSL lines.

core switches have static default route pointing to ASA

or also :

you can use OSPF on ASA and on R1 and R2 and you can have R1,2 to generate default routes propagated via ASA to core switches.

use on R1,2

router ospf 10

default-information originate type 1 metric 50

network .. area 0

The most difficult part is NAT:

if you don't get a public address block that can be routed via all 4 DSL links there is no chance to use all of them in a real load balancing schema.

By the way, 4 DSL lines for a site that have two C6500 core switches with FWSM looks like a little undersized.

How many users are on the site ?

Hope to help


acharyr123 Mon, 05/18/2009 - 19:40

Each ASDL is of 26 MB capacity & the no of users will be nearly 600..


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