A common frame-relay misunderstanding

The encapsulation type on the physical interface must be set to frame-relay
before any sub-interfaces can be created. The default encapsulation type is
usually HDLC (High-level Data Link Control).

So, before starting to create our frame-relay sub-interfaces, we need to first
set the encapsulation type to frame-relay on the physical interface:

	router>enable
	router#configure terminal
	router(config)#interface serial0
	router(config-if)#encapsulation frame-relay

Now we can create our sub-interfaces:

	router(config-if)#interface serial0.1 point-to-point
	router(config-if)#description This is our first sub interface for serial1

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Setting the bandwidth on serial links

Setting the bandwidth on a serial interface has nothing to do with the actual
link speed. Rather, it provides the value that some routing protocols use in
calculating routing metrics. The default bandwidth is 1.544mps, which is the
speed of a T1 link.

However, if you aren't using a T1, setting your bandwidth on serial links is
always a good (and sometimes forgotten) idea.

	router>enable
	router#configure terminal
	router(config)#interface serial0
	router(config-if)#description This is a 56k link
	router(config-if)#bandwidth 56