Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

Is it possible to configure serial interface with multiple IP addresses

I have a Cisco 2600 with four serial interfaces enabled and I have several external users that will connect via a PBX to the first available number or serial port. The users have cisco 1721 that are in their own subnet. Should I use ipunnumbered, because I don't know which user or subnet connects to my serial interfaces or is it possible to create subinterfaces for each of my serial interfaces to route. For example let's suppose the serial interfaces on the routers are in the 199.x.1.0/28 network and interfaces S0 /1 thru S0/3 on the 2600 are given addresses 199.x.1.1 -.4 and the serial 0 interface on the 1721s are given 199.x.1.5 thru 199.x.1.8. Can I assign a subinterface to each of the Serial 0/x interfaces to allow it route to any 1721 that might connect? If there is a better approach then please let me know.


Re: Is it possible to configure serial interface with multiple I

Hi Brian

Can you post a topological diagram representing the current connectivity and the requirement you have in place out there ?


Hall of Fame Super Silver

Re: Is it possible to configure serial interface with multiple I


I agree with Edwin that understanding your environment would help us to give you better advice. In a typical serial link it is a point to point connection and you know exactly what is connected on the other end of the line and it does not change. When you say that you do not know which interface the remote will connect on it sounds like you are describing a dial environment rather than a point to point serial.

There is one part of your question that is fairly easy to answer. When you ask about creating subinterfaces that is possible if your serial line is using frame relay encapsulation and not possible if your serial line is using HDLC or PPP.

If your serial lines are really ISDN connections then it might be that configuring dialer profiles would be the solution that you are looking for.