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New Member

Dial backup to central router

I am trying to provide dial-backup facility for 150 remote branches at the central router using NM-30DM modem module.

Since the modem module has 30 lines, I can have a pool of 30 IP addresses

at the central site for dial backup.

As the remote branches are devided in to 4 OSPF areas, I have to devide the central IP pool for dial backup also in to 4 groups and has to be dedicated one pool for each area. So a pool can have only 7 IP addresses to support 40 branches.

Is there any way that I can still have one single IP pool for dial backup and to support 4 OSPF areas ?

New Member

Re: Dial backup to central router

Two things you might want to try:

Allocate 4 subnets, one to each OSPF area. Each subnet will have enough host addresses to allocate one address per box in that area. This way you will not need to setup a pool at all. make one dialer interface per area.


Setup a few loopback interfaces, one per area and get your branches to connect using IP unnumbered. This method may break any summarising you may be doing only during dial-backup. Alternatively if you use loopbacks in Area 0, you won't have the above issue.

have fun...

New Member

Re: Dial backup to central router

Many thnaks for the reply.

I just need to clarify on the second method. ( I actually do not understand the

first method).

I believe that the config for the second method would look like this;


Interface group asynch 1

IP unnumbered loopback 0

no peer defalut IP address

group range 1 30


Here I have to assign entire range of lines ( 30 lines for 30 modems) in to a single asynch interface. Then I can only assign one loopback address for the interface. Therefor eI will not be able make use of more than one loopbacl addresses ?