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New Member

backup isdn line

How would I configure my router so that if the first isdn line is busy it uses a different number ?


Re: backup isdn line


Are u using a single bri port for u r isdn. if yes u can configure it by using this command in bri interface mode

router(config-if)#dialer load-threshold inbound or outbound or either

load value can be from 1-255

depending upon u r criteria of specifying the traffic flow the second channel is going to get activated.

VIP Purple

Re: backup isdn line


there is a command available that specifies the order in which multiple dialer strings are used:

dialer order

Basically, there are three options: sequential, round-robin, and last-successful.

Sequential - Always starts dialing the first dial string configured in a list of multiple strings, and continues to the next dial string when a call fails. This keyword allows dial string order to be prioritized, and is the default

round-robin - Always starts dialing using the dial string that follows the most recently used dial string. If no calls have previously been made, the dialer uses the first dial string. When a call fails, the dialer tries the next dial string until all dial strings have been tried. This keyword allows calls to be shared equally among the configured dial strings. However, if the dial strings are associated with multiple ISDN B channels on the same remote device, a call may be placed to bring up a second B channel without trying to call the number associated with the first B channel

last-successful - Always starts dialing using the most recently successful dial string, and continues to the next dial string in a list when a call fails. This keyword reduces the time needed to find a dial string that successfully completes a call when the dial strings are not likely to be equally successful

Check the comamnd reference for more info:

dialer order



New Member

Re: backup isdn line

yes im using a single bri port, can you please show me an example config, including the backup number, route etc ?, i thought the load threshold was to bring up another line incase the other one is at a certain load of traffic ?



Re: backup isdn line


As mentioned by GP in his post your best bet would be round robin option which you can pick up and configure under your dialer interface.

do check few config samples which shows on how to add up a secondary dialer string as well as a brief config sample taken from cco.

dialer string 12345678

dialer string 12345679

dialer order round-robin


interface Dialer0

ip address

encapsulation ppp

dialer pool 1

dialer string 1904

dialer string 1905

dialer string 1906

dialer string 1907

dialer-group 1

dialer order round-robin

As you have mentioned dialer load threshold option is to bring the second channel up when you want to make use of the other idle channel (based on your requirement) during load conditions which can add upto 128K(64+64).


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