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ADSL redundancy design

We have a remote site with 2 different departments located at it.

At the moment, they are connected to our head office via an ADSL link, with an IPSEC tunnel built between the Cisco 837 router at the remote site and our Head Office PIX515E firewall.

(Traffic for head office is routed over the IPSEC tunnel, they break out locally for internet access)

What we would like to do is install a 2nd ADSL connection to a different ISP.

And then have one department connected to Head Office via the ADSL connection to ISP A and the other department connected to Head Office via the ADSL connection to ISP B.

However, for resilience, if either of the ADSL connections fail, we would like the traffic for that department to automatically fail over to the other ADSL link.

Is this possible? If so, what would be the best way of achieving this?

New Member

Re: ADSL redundancy design

U need to use policy based routing or BGP proctol. I don't think so that ur router will support for BGP.

Re: ADSL redundancy design

hi mitchen,

i would like to say that its all depends on your existing network design and infrastructure... now you didnt specify that your both the connection are terminated at the same router or one connection from ISP-A is terminated at one router-A and other conncetion form ISP-B is terminated to the other router-B... you can have different type of feature as per the connectivity or you can say your existing network infrastructure...

i think you are talking about the two different department so i assume your both the ISP connection terminated at the different router then you can have GLBP and HSRP kind of thing... now you want to let your one department traffic should follow ISP-A path and other department traffic should follow ISP-B path then try for the HSRP with the two different standby group...but here you should consider the network topology also...means your both the router should be reachable to each other... now your IP addressing will also come in to the picture both the department should have different subnet... so you can use the different subnet virtual ip let one router be a active router for the one subnet and other router is the active router for the other subnet... and also check for that your router and IOS support the HSRP or not...

if you want more help on HSRP then let me know, you can have more information on this link:

now if your both the connection terminate with the same router then... if your network design is simple then use static route with variable AD...

letsay your one department is having ip addresses of 192.168.1.x and other is having 192.168.2.x... ISP A connection terminate at the interface A and ISP B connection terminate at the interface B then you can have two static route for one ip addresses range(configure static route for 192.168.1.x with default AD which point to the interface A and also with the AD of 100 which point to interface B and two static route for the other ip address range(configure statiroute for 192.168.2.x with default AD which pointing to the interface B and also with the AD of 100 which point to the interface A), so here you will have the redundancy also...

let me know if you want other help...

hope this will clear your idea...

rate this post if it helps



New Member

Re: ADSL redundancy design

Hi Devang,

thanks that is very helpful.

Just to clarify - at the moment we only have ONE ADSL connection with traffic from both departments going through the single connection.

We want to install a 2nd ADSL line and separate the traffic from each department so that they each have their own ADSL link (but can use the other department's ADSL connection if there was a failure)

So - what I want to try to decide is whether it would be best to either:

1) Keep existing Cisco 837 and buy similar router for the 2nd ADSL connection. Then, as you have described, it sounds like I could use HSRP or GBLP (not too familiar with GBLP but I assume its similar to HSRP but allows some form of load balancing?) to achieve resilience between the connections.


2) Replace the existing Cisco 837 router with another router altogether and have both ADSL connections terminate on the same router. Then, again as you have described, I could use static routes with variable adminstrative distances.

Any suggestions on which of the above would provide the best solution?

Re: ADSL redundancy design

hi Mitchen,

thanks for complement as well as rate the post...

you can have more information about the GLBP on this link:

but first of all check it out that your router provide the GLBP future or not...

i prefer to have two router... and different connection terminate to the different router... so it will have good redundancy... if you have one router and you terminate both ISP link to same router and if your whole router goes down then you will not have communication with the internet... so prefer to have the two different router with HSRP configuration (use two different standby group so you can have good redundancy)

i think following IOS suppor GLBP and may be your router support the following IOS:12.4(9)T 12.3(11)YS1 12.3(11)YK2 12.3(11)T9 12.3(8)YG4 12.3(8)YA1 12.3(8)T9

12.3(7)XR6 12.3(7)T9 12.3(4)XG1 12.3(4)TPC11a 12.3(4)T9 12.3(2)XE4 12.3(2)XC2 12.3(2)XA5

hope this will help you

rate this post if it helps



New Member

Re: ADSL redundancy design

hi Devang,

thanks again for the further advice.

Having 2 routers probably works best for us too - as it should be cheaper to simply buy an additional Cisco 837 rather than a router which would support 2 WIC1-ADSL cards!

I've checked on the router we have currently and the GLBP commands are there so it all looks good!

Hopefully it will all be as straightforward as it sounds!

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