Subinterfaces
You apparently apperceive by now that you can accept assorted basic circuits on a distinct serial
interface and yet amusement anniversary as a abstracted interface—I mentioned this earlier. You can accomplish this
happen by creating subinterfaces (see Table 11.11). Think of a subinterface as a analytic interface
defined by the IOS software. Several subinterfaces will allotment a distinct accouterments interface,
yet for agreement purposes they accomplish as if they were abstracted concrete interfaces, something
known as multiplexing.
To configure a router in a Anatomy Relay arrangement so it will abstain breach border issues by not
permitting acquisition updates, aloof configure a abstracted subinterface for anniversary PVC with a unique
DLCI and subnet assigned to the subinterface.
TABLE 11.11 Subinterface Commands
Command Meaning
interface interface Chooses the interface you are
connecting Anatomy Relay to
encapsulation frame-relay Sets the Anatomy Relay
encapsulation to Cisco
encapsulation frame-relay ietf Sets the Anatomy Relay
encapsulation to IETF
interface interface.subinterface_number point-topoint
Creates a point-to-point subinterface
interface interface.subinteface_number multipoint Creates a multipoint subinterface
You ascertain subinterfaces application a command like int s0.subinterface number. First, you
have to set the encapsulation on the concrete consecutive interface, and again you can ascertain the subinterfaces—
generally one subinterface per PVC. Here’s an example:
RouterA(config)#int s0
RouterA(config-if)#encapsulation frame-relay
RouterA(config-if)#int s0.?
<0-4294967295> Consecutive interface number
RouterA(config-if)#int s0.16 ?
multipoint Amusement as a multipoint link
point-to-point Amusement as a point-to-point link
RouterA(config-if)#int s0.16 point-to-point
You can ascertain a austere bulk of subinterfaces on any accustomed concrete interface, but keep
in apperception that there are alone about 1,000 accessible DLCIs. In the above-mentioned example, I chose to
use subinterface 16 because that represents the DLCI cardinal assigned to that PVC by the carrier.
There are two types of subinterfaces:
Point-to-point Used back a distinct basic ambit connects one router to another. Anniversary pointto-
point subinterface requires its own subnet.
Multipoint This is back the router is the centermost of a brilliant of basic circuits that are application a
single subnet for all routers’ consecutive interfaces affiliated to the anatomy switch. You’ll usually find
this implemented with the hub router in this approach and the batten routers in concrete interface
(always point-to-point) or point-to-point subinterface mode.