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Webcast-Catalyst9k
New Member

ADSL and dialer interface

Hi

I was wondering if you can use things such as dialer watch when you use a dialer interface on an ADSL connection. I have an ADSL connection I don't want used unless my main leased line goes down so I want to keep the interface down until needed. I'll get a chance to test this later this week but would be interested if anyone knows the answer beforehand.

Thanks, Stephen.

6 REPLIES

Re: ADSL and dialer interface

hi

You can try make use of 2 static default routes with and without some metric attached to them respecitively.

the one without metric pointing towards your serial which can act as your primary one and the other with metric towards the dialer which can act as your secondary link..

regds

New Member

Re: ADSL and dialer interface

Actually the issue I see is coming from the far end of the ADSL link. The traffic leaving my site goes via the leased line as I want but traffic coming into my site from another with only ADSL access uses my sites ADSL backup link. The issue is that both ADSL connections terminate on the same BAS and as such the are connected routes on the BAS. I want the BAS only to have a direct connection to sites using ADSL as a backup when the sites main connection goes down. So I want to only bring the backup adsl connection into use, and be seen as connected at the BAS, when I want it to. Like getting an ISDN link only to dial when you want it to.

Re: ADSL and dialer interface

Hello,

I am not really clear on the configuration of your BAS, are you saying that you have several ADSL connections terminating on the BAS, and you want to use the serial line to be used primarily (for outgoing traffic), and one of the ADSL connections as a backup for the outgoing traffic, while that same ADSL connection is being used by the remote site for incoming traffic ? In that case, you obviously cannot use the 'backup interface' command on the serial line.

You might want to have a look at object tracking, which basically allows you to make routing decisions based on criteria such as ICMP reachability, or line protocol status of an interface. Check the following link from the documentation CD for details:

Enhanced Object Tracking

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t15/fthsrptk.htm

HTH,

GNT

New Member

Re: ADSL and dialer interface

The configuration is;

A site has a leased line terminating on a router intended to take all traffic to and from a site under normal circumstances. There is another router on the site with an ADSL line intended as a backup to the leased line. So for traffic leaving that site I can easily choose that it goes via the leased line. The ADSL terminates on a particular BAS which receives a per-user static route from a radius server once ppp authentication occers.

Now, a second site only has an ADSL line. It terminates on the same BAS. So when traffic from that site hits the BAS going to the site with ADSL as backup it sees a static route with an AD of 1 via what is supposed to be the backup ADSL line and it sends traffic that way. If the backup ADSL line wasn't up there is another route that will go to a PE and over the leased line. The radius server is sending the per-user static route with an AD of 210 but the BAS seems to ignore this and installs it with AD of 1 hence beating the dynamic protocol AD.

My thought was since the ADSL line is configured as a dialer we could try to emply some of the ISDN type dialer configurations to keep the line from coming up and authenticating until it is needed and therefore keeping the per user static route out of the BAS routing table until the line is needed.

I have no idea why the BAS is not accepting the AD of 210 supplied by Radius but I am not in control of that part of the circuit. I am in control of the ADSL router used for backup and as such hoped there was something I could do there to influence the problem. I could run a routing protocol but wanted to try and see if I could keep the ADSL down somehow first.

S.

Re: ADSL and dialer interface

Hello,

thanks for the explanation. The only way I can see the traffic going through the serial line is by having the ADSL backup interface in a down or disabled state. How about putting both the serial and the ADSL backup interface in an HSRP group, and making sure that the serial interface is on the active router ? Would that be a feasible solution for you ?

Regards,

GNT

New Member

Re: ADSL and dialer interface

"is by having the ADSL backup interface in a down or disabled state"

I agree. Which is what I'd like to do but then dynamically bring the ADSL connection into use when needed. The hsrp will work for traffic leaving the site. The 2 routers will share a common LAN and the serial router is HSRP active. But coming in it won't work. The BAS and the PE that terminates the serial line don't necessarily share a common LAN to run hsrp on.

S.

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