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Configuring point to point T1 interface

Hi All,

I recently took CCND1 and 2.  I understand that for a router serial interface configuration I need to use the "interface serial X/X" command, along with the chosen IP address and associated mask, and so on.  In fact, I had done so in a similar configuration on a 2811 once before with success.

I recently was tasked with configuring a similar interface for another 2811; the new serial interface will be using slot 1, as slot 0 is in use with a dual T1 card.  The new card is a dual port T1 as well.

My problem is that, upon looking at the running config of the router, the person who configured it used the "controller T1" command as well.  Back in ICND, we didn't touch on the "controller" command, so I am not sure why or if is needed, and why.

Can anyone shed some light into this?

Thanks in advance,


Hall of Fame Super Silver

Re: Configuring point to point T1 interface

Hello Jose,

the controller T1 object is used to define physical layer properties.

This is typical of modules that can be used to interface with ISDN network, so in controller T1 context you define how the 23 B channels are used.

For data applications the controller T1 can create a logical serial interface putting all B channels in a single channel-group or using channel-group 0 unframed

a serial interface 0/1/0:x  where x is the channel-group is created as a result  of this.

on the interface you can apply the encapsulation and other commands to give an IP address and so on.

Some modern modules for ISR routers do not use an external controller T1 object but have service-module t1 commands inside the serial interface.

so it is possible in the same routers that T1 ports of different modules look like configured differently as you have noted

Hope to help


Hall of Fame Super Silver

Re: Configuring point to point T1 interface


As Giuseppe points out, whether you need the controller T1 command or not depends on the type of card used for the new T1 in the router. Many of the older cards did not use the controller T1 command. Many of the newer cards (especially cards that allow you to use them for either T1 or E1 circuits) do require the controller command.

ICND does not focus on some things like the controller T1 command because ICND is more focused on what are the fundamentals required to make an interface work (things like IP address, subnet mask, and for serial interfaces things like encapsulation). ICND assumes that some things such as controller T1 are things that you will encounter and will figure out as you perform network configuration tasks that are more sophisticated than what is the focus of ICND.



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