Cisco Support Community
Community Member

ISDN Dialer routing Problem


We have simple network of three routers rtrA, rtrB and rtrC. rtrA is connected to rtrB via leased line and rtrB is connected to rtrC by another leasedline.

rtrA has network A, rtrB has networkB and rtrC has networkC connected to them on ethernet respectively. All routers have static routes for these networks configured in them. And also has default route to next hop address of link. So far so good. We are getting connectivity from all networks to all other networks.

ISDN BRI is configured as a backup to these links using dialers. And routerB calls to routerA or also to router C or to both router A and also to router C similtaneously. There are two dialers configured on router B one to call router A and another to call router C.

Corresponding incoming dialers are configured on router A and router C which accept the calls from router B.

In short simple configuration for dialers is as below

router A

dialer 0 ( to accept incomig call from router B)

Router B

dialer 10 ( to call router A )

Dialer 20 ( to call router B )

Router C

Dialer 30 ( to accept call from router C)

In router B both dialer have same IP address. Do we need ip address of these dialers also in the same subnet or we need to use two separate subnets for two links.

How do I give static routes using dialer ?

Thanks in advance



Re: ISDN Dialer routing Problem


You must be using 'ip unnumbered' config on RouterB as you stated the dialer interfaces are using the same IP address. As long as you can provide a unique IP address to Router A and Router C from the same subnet as Router B's dialer interfaces then you can use the same subnet for both dialer interfaces on Router B.

PPP, by default, populates a host route, i.e a route with a /32 bit mask, and thus you can configure floating static routes on all the routers to point to the far end DDR interface IP address.

You need a config like the one below.

Router B:

int lo0

ip add

int dialer 10

ip unnumbered lo0

int dialer 20

ip unnumbered lo0

ip route (NET_A) 250

ip route (NET_B) 250

Router A:

int dialer 10

ip add

ip route 250

Router C:

int dialer 30

ip add

ip route 250

Hope that helps!



CreatePlease to create content