Basic T1 Configuration Question

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Apr 30th, 2007
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I have an old router that is in production, and has been working fine to the best of my knowledge, for a while. It was sent to me from corporate, and I am trying to document it as best I can. I went in and discovered some oddities with it, and was wondering what they meant. This is what the config is, in part:


controller T1 0/1/0

framing esf

linecode b8zs

channel-group 0 timeslots 1-24

!

interface Multilink1

no ip address

ppp multilink

ppp multilink group 1

!

interface Serial0/1/0:0

ip address 5.6.7.9 255.255.255.252

ip load-sharing per-packet

!


My confusion comes from several things; the lack of any ppp commands on the serial interface; the :0 at the end of the serial interface number; and the use of the channel group time slots (does that mean its a channelized T1(PRI)?

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mohammedmahmoud Mon, 04/30/2007 - 10:14
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Hi,


First of all, the whole T1 time slots (1-24) were grouped in one channel "channel-group 0 timeslots 1-24" and thus it is not channelized.


Second the multilink configuration is irrelevant, since it is not linked to the serial interface.


Third the :0 serial interface is the interface that was created automatically after entering the "channel-group 0 timeslots 1-24" command, in order to be configured.



HTH, please rate if it does help,

Mohammed Mahmoud.

ron.carney Mon, 04/30/2007 - 10:44
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Thank you so much! So, the channel-group - timeslots 1-24 bundles all of the channels into 1 group, addressable by adding the :) to the end of the interface number, correct?


And, the multilink interface and its subcommands have NO effect, because the serial interfaces have no encap ppp/ppp multilink/multilink group 1/ commands, is that correct? If i wanted to enable multilink on the three T1's, would this be all that is necassary?


interface Serial0/1/0:0

encap ppp

ppp multilink

ppp multilink group 1




mohammedmahmoud Mon, 04/30/2007 - 10:52
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Hi Ron,


Perfect Ron, yes you've got it all correct.


Please don't hesitate for any further questions.


HTH,

Mohammed Mahmoud

Richard Burts Mon, 04/30/2007 - 10:20
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Ron


It is interesting and inconsistent (based on what you have posted) to have the multilink configured on the router. It is odd (and makes me think that it is inactive) that the multilink has no ip address configured. From what you have posted I believe that the serial interface is using HDLC encapsulation and not ppp. If you post the output of show interface and show ppp multilink it could confirm this.


The :0 at the end of the serial interface number is an indicator that you are configuring the control channel of the T1 which is defined in controller T1 0/1/0. It uses the channel-group timeslots to indicate that this is a full T1 (not partial).


HTH


Rick

ron.carney Mon, 04/30/2007 - 10:42
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Rick,

A show int confirms encap is default of HDLC, which also confirms the ppp multilink is no active.


What you say regarding the :0 has me slightly confused, I understood from Mohammed that because the channels were put in a group (group 0) that the :0 addressed that group? From what you are saying regarding it addressing the control channel, it should be :23, isn't that the D channel?


Thanks for your help, Rick.


Ron

mohammedmahmoud Mon, 04/30/2007 - 10:50
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Hi Ron


When Rick said that it is addressing the control channel he didn't mean the D channel (D channel is only said when the T1 is configured as a PRI, which is not the case).


HTH,

Mohammed Mahmoud.


ron.carney Mon, 04/30/2007 - 10:52
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Ok thank you, then I understood you (both.) Mohammed, what would it take to correctly configure multilink on the interface(s)? See above where I posted what I thought it would take...

mohammedmahmoud Mon, 04/30/2007 - 10:57
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Hi Ron,


Perfect Ron, yes you've got it all correct, under the 3 serials:


no ip address

encap ppp

ppp multilink

ppp multilink group 1


Please don't hesitate for any further questions.


HTH, please rate if it does help,

Mohammed Mahmoud


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