02-27-2006 01:39 PM - edited 03-03-2019 11:53 AM
Hi All,
A quick question on serial interfaces. Is it really necessary to have sub interfaces on point-to-point connections? I understand the need when running ATM or frame or something of the sort, but for a standard ppp config with one ip? why would you need to confuse things any farther? i keep seeing configs with sub interfaces and just wonder if i am doing something wrong or what.
Thanks
02-27-2006 01:50 PM
Hi,
Perhaps someone else may correct me, but to the best of my knowledge you can't configure subinterfaces on a ppp link. Can you post the config?
I agree with you, I am all for keeping things simple..-)
Rgds
E.
02-27-2006 01:56 PM
The following is from an ATT router config guide:
interface serial x/y:z
ip address
encapsulation ppp
no peer neighbor-route
no cdp enable
framing c-bit
dsu mode 0
dsu bandwidth
Now by no means am I saying that the guide is correct, but I just wanted to make sure as this is supposed to help me, not confuse things! ;)
02-27-2006 01:56 PM
Hi,
Sure, there's nothing wrong with configuring a PPP serial connection with an IP.
example:
interface Serial0
ip address 10.1.1.1 255.255.255.0
encapsulation ppp
HTH,
Bobby
02-27-2006 01:58 PM
So I suppose its really up to the person doing the configuring? lol
I just wanted to make sure I was not going against some age old cisco "best practice". the way i see it, i just want to keep things as simple as possible!
thanks
02-27-2006 01:57 PM
Hello,
For a basic "non-channelized" point-to-point ckt connection you do not need to have subinterfaces. If you have say a T1 controller or external CSU/DSU you can add an IP to the repsective Serial interface an add whatever encapsulation you like.
However, if you have a circuit that has channelized connections off of it you will need the subinterfaces (e.g you have a T3 that is channellized into 28 T1s (all point-to-point) you would need to have that many sub-interfaces).
HDLC is default encap type for Serial interfaces. If the enccap matches both ends you should be okay. You don't need a subinterface for PPP to work either.
Hope this helps.
Regards,
James
02-27-2006 02:20 PM
Hi James,
I thought those were classed as logical interfaces and not subinterfaces.
Rgds
E.
02-27-2006 07:06 PM
Hi,
I think your point of confusion with the config you supplied is that you are thinking that the 'z' refers to a sub-interface number. That is not the case. The 'z' refers to a channel-group neighbor.
interface serial x/y:z
ip address
encapsulation ppp ...
When you have interfaces such as a T1 or an E1, you can configure multiple channels on them, as follows:
controller e1 0/1
channel-group 1 timeslots 1-10
channel-group 2 timeslots 11-20
Each of the channel-groups will result in the creation of a serial interface. For example, for the above case, the serial interfaces would be:
serial0/1:1 ! for channel-group 1
serial0/1:2 ! for channel-group 2
Each of the above is a physical (main) interface, not a sub-interface.
Note that when using T1 cards with builtin CSU/DSUs you don't get the ability to configure the T1 controller - all the config appears under the serial interface.
Hope that helps - pls rate the post if it does.
Paresh
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