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New Member

Setting up leased line using 2 1721's...

Hi there,

I have no experience of Cisco devices at all, but in the new year I will have to setup a leased line between 2 Cisco 1721 routers both with a WIC-1T.

Here is the setup. At our head office we have about 20 pc's running Windows 2k, 1 server running SBS 2k3 and a 512 ADSL connection to the 'Net. At the branch office we have 5 pc's working in a workgroup again with a 512 ADSL connection. At the moment the 2 networks are connection using a VPN using 2 Draytek Vigor 2600's.

The VPN is not fast enough so British Telecom are laying a 1 meg each way leased line. The cabling will be X.21 inside the building

Does anyone know how difficult it will be to setup the 2 1721's to use the leased line? Is there a standard config? Do Telecom companies usually provide settings?

Any help, advice, or pitfalls would be appreciated.

Thank you,


VIP Purple

Re: Setting up leased line using 2 1721's...

Hi James,

setting up the leased line connection with two Cisco 1721 routers is pretty sraightforward, there are no real pitfalls. What you need to configure on your WICs is the following (I have used the names 1721_HEAD for the head office router and 1721_BRANCH for the branch office router. It is customary to use a /30 subnet, in order to save address space. The address space I have used in this example is You might be using different router names and IP addresses):

1721_HEAD#conf t

1721_HEAD(config)#interface serial0

1721_HEAD(config-if)#encapsulation ppp

1721_HEAD(config-if)#ip address

1721_HEAD(config-if)#no shut


1721_BRANCH#conf t

1721_BRANCH(config)#interface serial0

1721_BRANCH(config-if)#encapsulation ppp

1721_BRANCH(config-if)#ip address

1721_BRANCH(config-if)#no shut




New Member

Re: Setting up leased line using 2 1721's...

Hi, and thanks for your reply.

I'm relived to hear that it is a fairly straightforward setup.

I'm planning on using the ADSL connections each end to still provide Internet access to both sites. After configuring the routers would I be right in saying that I would simply have to setup a static route on each of the ADSL modems to point to the other network the oppsosite side of the leased line.

I hope this makes sense to you, and thanks again for your reply.


VIP Purple

Re: Setting up leased line using 2 1721's...


I am not sure I understand 100% what you are saying: if you have the two sites connected with the WICs, and the ADSL connections will still be used to give Internet access to the users, you will need a static route on each router pointing to the network in the other site, but for Internet access you need just a default route of on each router, pointing towards your ADSL. I assume that you are using private space addresses on your network, so just add a specific route for your networks on each site and then a default route towards the Internet.



New Member

Re: Setting up leased line using 2 1721's...

Hi again,

I think I've got it now. So on both ADSL routers I set the default route to

Then on both ADSL routers set a static route to point to the other network.

Thanks, James.

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