How to configure ISDN Interface on a other router as backup interface

[ciscorajeev]

Hi,

We have two routers (Cisco2811) one has the E1 Terminated on it and the other has the ISDN Link Terminated on it, We would like to use he ISDN Link as a backup link to the Primary E1 Link.

I am aware of the Backup Interface concept and I would like to clarify whether we can configure floating static routes and make the second FastEthernet Interface as a backup interface to the Primary E1 Interface.

If so I would like to know whether this works or not.

Any reply on this is appreciated.

Regards,

Rajeev Ahobala

[desai.jaideep]

Hi

(1)You can enable RIP on all routers.It will take care of the back-up connection.

(2)You can add an interface as backup by

"contr e1 0

backup interface bri 0

backup delay 1 1"

and in default route, give the metric "50"

"ip route 0.0.0.0 0.0.0.0

ip route 0.0.0.0 0.0.0.0 50"

Hope it helps.

Regards

JD

[ciscorajeev]

Yes we are very much aware about this configuration , But in this scenario the backup interface is on the other router i.e on a different hardware.

Can we enable the second fastethernet interface on the router as backup interface

[AmandMimoza]

Hi,

I think that this solution :

1. Configure HSRP for the BLR2811-A & BLR2811-B with major priority router BLR2811-A

( hsrp group 1 priority 150 ) for router BLR2811-A

( hsrp group 1 priority 100 ) for router BLR2811-B

2. Configure HSRP with track serial 1

track 1 interface serialY/Y:Y.Y line-protocol -> BLR2811-A

That means: when s1 go down all the traffics will bee redirects to the router BLR2811-B and isdn go up.

3.Routing ( case without routing protocol )

Define a default route / statick route :

0.0.0.0 0.0.0.0 s1 BLR2811-A

0.0.0.0 0.0.0.0 dialerX BLR2811-B

------------------------------------------------------------------------------------------------------------------------

An other one is to add one default route / static route to fa0/0/0 with different weigh:

0.0.0.0 0.0.0.0 s1 BLR2811-A

0.0.0.0 0.0.0.0 f0/0/0 200  BLR2811-A

0.0.0.0 0.0.0.0 dialerX BLR2811-B

[devang_etcom]

hi rajeev...

here you are having some what complex thing...

as you are having primary link as E1 and secondary is ISDN and both are on different router...you have to deploy the HSRP... and along with that you have to think about the ISDN firering... it means you have to keep your ISDN line active and i think its costly to you... so better to go for the HSRP with load sharing fundamental so you can have the utilisation of your fired ISDN link...

or you can have like dont configure the standby x track on the router with isdn connection ... but it is not recomandad... so when your E1 link goes down then router with ISDN will become active router and your configure intresting traffic will fire the ISDN link...

let me know after implementaion... so i can also have idea

rate this post if it helps

regards

Devang

[devang_etcom]

one other way is to user recursive route lookup kind of thing...

let say your routerA with E1 link and routerB with ISDN link... router A and routerB both are connected using FE ports...

now configure the two default route with the different AD on router A one default route with lowest AD point to E1 link and other default route with the higer AD point to the FE port...

ip route 0.0.0.0 0.0.0.0 IPaddress of interface with E1 link

ip route 0.0.0.0 0.0.0.0 IP address of FE to routerB metric 13

here router A will select the first default route as primary... so when the E1 link goes down then other static default route with higher AD come into the picture...

now on route B configure the default route which is pointing to the dialerinterface of the ISDN...so when traffice of router A come to the routerB because of E1link down...it will travel to the internet using ISDN link...

ip route 0.0.0.0 0.0.0.0 dialerinterface

try to deploy it and reply me whether it works or not...

hope this configuration will work

rate this post if it helps

regards

Devang

[jackyoung]

I prefer to use HSRP too, it can provide one more protection on the primary router or LAN down. Please ensure what traffic should trigger the ISDN and the length of the idle timer to drop the ISDN call. You may also need to consider the return path if the primary E1 down, how the remote call traffic route back via ISDN. You may need to add a floating static route that point to the ISDN at remote end.

[Wilson Samuel]

Hi Rajeev,

We have a similar situation in place where in if the primary interface goes down the secondry link being on the other Router kicks in.

However looking at your diagram, may I say that the Cross Cable connections in the Routers actually are not neccessary as both the Routers could be terminating to different switches / same switches within the same VLAN.

Secondly, all you need to do is, to configure that a Dialer Interface with interesting traffic to opposite site and also create HSRP for both the Routers. Thats It!!

Hope it helps, please respond if you have sorted out the issue or still anything is required.

Kindly rate if it helpds.

Kind Regards,

Wilson Samuel

[ajaykumar2k1]

Dear Rajeev

The solution for this is

We will runn HSRP at both Chennai and Blr .Primary routers will be Router A at both end and we will track the serial link .When the serial link will go down the router B become active and pass traffic through ISDN .

ISDN we have to configure for Dial on demand.

Regards

Ajay Kumar

[jackyoung]

There is another issue of the return traffic : If Bir router A's WAN down, the HSRP will be triggered and change router B as GW. However, at Chennai, router A WAN may still up, so the HSRP will not be triggered and keep it as GW, so the traffic from Chennai to Bir will go through Chennai router A --> router B --> ISDN --> Bir router B --> user. You will require the inter-link between two local routers. But you require to maintain the routing protocol between router A & B at local site.

Or you can remove the inter-link and enable tracking between router A LAN - A LAN, router B LAN - B LAN. It tracks the LAN interface instead of the WAN interface status. If remote LAN can be reached, then it continue to use this router as GW, other change to secondary router as GW. It is the same at remote side, if remote router cannot reach local router's LAN then remote router will change GW to secondary router.

Check below for more info.:

http://www.cisco.com/en/US/products/ps6566/products_feature_guide09186a008063c9bf.html

Hope this helps.