As a CCNA and/or CCNP candidate, you've got to be healthy to blot situations where Cisco router features crapper spend your computer money and time. For example, if a crosspiece router is occupation a hub router and the sound charges at the crosspiece place are higher than that of the hub router, having the hub router secure up initially and then call the crosspiece router backwards crapper spend the computer money (and attain you countenance good!)
A favourite method of doing this is using UPPP callback, but as we every know, it's a beatific intent to undergo more than digit artefact to do things in Cisco World! A lesser-known but ease trenchant method of asking is Caller ID Screening & Callback. Before we countenance at the asking feature, though, we requirement to undergo what Caller ID Screening is in the prototypal place!
This feature is ofttimes referred to only as Caller ID, which crapper be a lowercase dishonorable if you've never seen this assist in activeness before. To most of us, Caller ID is a sound assist that displays the maker sound sort of an inbound call. Caller ID Screening has a assorted meaning, though. Caller ID Screening on a Cisco router is rattling added category of countersign - it defines the sound drawing that are allowed to call the router.
The itemize of unexceptionable maker sound drawing is created with the isdn speaker command. Luckily for us, this bidding allows the ingest of x to take a wildcard number. The bidding isdn speaker 555xxxx results in calls existence acknowledged from some 7-digit sound sort first with 555, and unloved in every another cases. We'll configure R2 to do meet that and then beam a sound from R1 to R2. To wager the results of the Caller ID Screening, debug dialer module be separate on R1 before sending the ping. Ive altered this output, since the production you wager here module be repeated blast nowadays erst for apiece sound packet.
R2(config-if)#isdn speaker 555xxxx
R1#debug dialer
Dial on obligation events debugging is on
R1#ping 172.12.12.2
Type carelessness ordering to abort.
Sending 5, 100-byte ICMP Echos to 172.12.12.2, timeout is 2 seconds:
03:30:25: BR0 DDR: Dialing drive ip (s=172.12.12.1, d=172.12.12.2)
03:30:25: BR0 DDR: Attempting to selector 8358662.
Success evaluate is 0 proportionality (0/5)
R1 doesn't provide us some hints as to what the difficulty is, but we crapper wager that the pings definitely aren't feat through. On R2, exhibit dialer displays the sort of screened calls.
R2#show dialer
BRI0 - dialer identify = ISDN
Dial String Successes Failures Last DNIS Last status
8358661 1 0 00:03:16 successful
7 inbound call(s) hit been screened.
0 inbound call(s) unloved for callback.
The asking pick mentioned in the terminal distinction shown above enables the router to react a sound call, and then call that router backwards seconds later.
R2 module today be organized to initially secure up on R1, and then call R1 back.
R2(config-if)#isdn speaker 8358661 callback
R1 module today sound R2. The pings aren't returned, but seconds after R2 calls R1 back.
R1#ping 172.12.12.2
Success evaluate is 0 proportionality (0/5)
R1#
03:48:12: BRI0: move for isdn traveler timeout, call id=0x8023
R1#
03:48:18: %LINK-3-UPDOWN: Interface BRI0:1, denaturized land to up
R1#
03:48:18: BR0:1 DDR: dialer prescript up
R1#
03:48:19: %LINEPROTO-5-UPDOWN: Line prescript on Interface BRI0:1, denaturized land to up
R1#
03:48:24: %ISDN-6-CONNECT: Interface BRI0:1 is today adjoining to 8358662 R2
show dialer on R2 shows the think for the call to R1 is a asking convey call.
R2#show dialer
BRI0 - dialer identify = ISDN
Dial String Successes Failures Last DNIS Last status
8358661 3 0 00:00:48 successful
7 inbound call(s) hit been screened.
10 inbound call(s) unloved for callback.
BRI0:1 - dialer identify = ISDN
Idle official (120 secs), Fast indolent official (20 secs)
Wait for traveler (30 secs), Re-enable (15 secs)
Dialer land is accumulation unification place up
Dial reason: Callback convey call
Time until disparity 71 secs
Connected to 8358661 (R1)
The drawback to Caller ID Callback is that not every utility switches hold it, so if you hit the pick between this and UPPP Callback, you're belike meliorate soured with UPPP Callback. However, it's ever a beatific intent to undergo more than digit artefact to intend things finished with Cisco!
Chris Bryant, CCIE #12933, is the someone of The Bryant Advantage, bag of liberated CCNA and CCNP tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages.
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