
MTU 1500 bytes, BW 64 Kbit, DLY 20000 usee, rely 255/255, load 1/255 Encapsulation PPP, loopback not set See the second part of Example 11-5 for the output of the show isdn status that you would see if you entered the command immediately after the show interfaces bri 0 command, whose output is shown on the top portion of Example 11-5.Įxample 11-5 Checking ISDN Layer 2's StatusīRI0 is up, line protocol is up (spoofing) Hardware is BRI The real status of Layer 2 is reported by the show isdn status command. I suggest that you use the show interfaces bri number command to make sure that the interface is not shutdown and more importantly, to read the throughput, error statistics and carrier transitions accounting information that it provides. For instance, if you disconnect the cable from the BRI0 interface of your router and enter the show interfaces bri 0 command, you will find out that even though the BRI0 interface is not connected to anything, it is still reported as up, line protocol up (spoofing) (see Example 11-5). Even though the BRI interface being reported as up and the line protocol being reported as up (spoofing) is necessary, it is not a sufficient condition for you to assume Layer 1 to be intact and operational. If the BRI interface under investigation (say, BRI0) is not shut down, the first line of the output should say: BRI0 is up, line protocol is up (spoofing). As stated earlier, Layer 1 will not come up if the physical connectivity is not in place, any of the relevant physical components are faulty, or if the BRI interface is shutdown (or not up for any reason, including faulty interface hardware).Įxample 11-4 Sample Output of the show isdn status Command B_BackR#show isdn statusĪnother command that is useful at this stage is the show interface BRI number command. If ISDN Layer 1 is not active, you should naturally focus on bringing Layer 1 up first. If ISDN Layer 2 is reported as NOT Activated, you must first find out if ISDN Layer 1 is ACTIVE or DEACTIVATED (see Example 11-4). The show isdn status command can be used to discover the status of ISDN Layer 2.

The LAPD protocol is formally specified in ITU-T Q.920 and ITU-T Q.921. LAPD delivers control and signaling information between the TE (the router, for instance) and the ISDN switch. The LAPD protocol is used for this purpose.

ISDN Layer 2 is concerned with the communication between the TE and the ISDN switch over the D channel.
