Leased line, 1 ISDN lines Backup configuration

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Jan 27th, 2009
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Hi all,

I have a router with one leased line, one isdn line, where LL is the primary connection to HO, and isdn line is the backup.

now i have a DR site where in case both LL and ISDN fails to head office, it should diasl out to DR site.

How can i configure second option in the same ISDN on the same router.

Thank you all for in advance for the help.

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Overall Rating: 5 (2 ratings)
Danilo Dy Tue, 01/27/2009 - 22:06
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ISDN-PRI or ISDN-BRI? Destination IP/Port the same?

Try this;

interface Dialer0

ip address w.x.y.1 << Note: HO should be w.x.y.2/29 and DR should be w.x.y.3/29

encapsulation ppp

dialer pool 1

dialer idle-timeout 600

dialer string HO_Dialer_String

dialer string DR_Dialer_String

dialer-group 1

ppp authentication chap

ppp multilink


dialer-list 1 protocol ip list 100


access-list 100 permit ip source_ip source_mask destination_ip destination_mask

When LL to HO fails, it will trigger ISDN to dial the first Dialer_String (HO ISDN Number), if it fails it will trigger the second Dialer_String (DR ISDN Number). You decide on the routing (use floating static route).

pradeepadias Tue, 01/27/2009 - 23:00
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Hi Medan,

I use different IP range in DR site ISDN, even the is it possible.?


Danilo Dy Wed, 01/28/2009 - 02:03
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It is possible (it works for both) that configuration actually I use for ISDN-BRI with HO and DR IP range differs. The remote site of course will/should try to connect to DR site IP Address range when they could not connect to HO IP Address range. Take note that the ISDN Interface of 3 routers should use an IP Addresses in the same broadcast /29. You also have to put the destination IP Address range in the same ACL.

If its ISDN-PRI, the configuration differs a little bit.

binoyjosephstanly Tue, 01/27/2009 - 22:19
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hi pradeep,

please look into this config,i think this matches your scenario.

pls rate if it helps



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