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
Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: