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Cisco Certification Exam Command Review:

ISDN and PPP

By Chris Bryant, CCIE #12933

backup load, backup delay, backup interface - All self-explanatory; make sure you know the meanings of each value shown below.

R1(config-if)#backup interface bri0

R1(config)#int s0
R1(config-if)#backup delay ?
<0-4294967294> Seconds
never Never activate the backup line

R1(config-if)#backup delay 20 ?
<0-4294967294> Seconds
never Never deactivate the backup line

R1(config-if)#backup delay 20 60

R1(config-if)#backup load ?
<0-100> Percentage
never Never activate the backup line

R1(config-if)#backup load 50 ?
<0-100> Percentage
never Never deactivate the backup line

R1(config-if)#backup load 50 25

compress, show compress -- The first command sets the compression method; the second verifies that method and shows compression statistics.

R2(config-if)#compress ?
mppc MPPC compression type
predictor predictor compression type
stac stac compression algorithm

R2#show compress

Serial0
Software compression enabled
uncompressed bytes xmt/rcv 0/0
compressed bytes xmt/rcv 0/0
1 min avg ratio xmt/rcv 0.000/0.000
5 min avg ratio xmt/rcv 0.000/0.000
10 min avg ratio xmt/rcv 0.000/0.000
no bufs xmt 0 no bufs rcv 0
resyncs 0
Additional Stacker Stats:
Transmit bytes: Uncompressed = 0 Compressed = 0
Received bytes: Compressed = 0 Uncompressed = 0

debug isdn q921 - Debugs the d-channel at the Data Link layer.

R1#debug isdn q921
ISDN Q921 packets debugging is on
R1#show debug
ISDN:
ISDN Q921 packets debugging is on

14:37:20: ISDN BR0: RX <- RRp sapi=0 tei=66 nr=12
14:37:20: ISDN BR0: TX -> RRf sapi=0 tei=66 nr=9

14:37:23: ISDN BR0: RX <- RRp sapi=0 tei=66 nr=12
14:37:23: ISDN BR0: TX -> RRf sapi=0 tei=66 nr=9

debug isdn q931 - Debugs the d-channel at the Network layer.

R1#debug isdn q931
ISDN Q931 packets debugging is on
R1#ping 172.12.12.2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.12.12.2, timeout is 2 seconds:

13:53:19: BR0 DDR: Dialing cause ip (s=172.12.12.1, d=172.12.12.2)
13:53:19: BR0 DDR: Attempting to dial 5554444
13:53:19: ISDN BR0: TX -> SETUP pd = 8 callref = 0x09
13:53:19: Bearer Capability i = 0x8890
13:53:19: Channel ID i = 0x83
13:53:19: Keypad Facility i = '5554444'
13:53:19: ISDN BR0: RX <- CALL_PROC pd = 8 callref = 0x89
13:53:19: Channel ID i = 0x89
13:53:19: ISDN BR0: RX <- CONNECT pd = 8 callref = 0x89
13:53:20: %LINK-3-UPDOWN: Interface BRI0:1, changed state to up
13:53:20: ISDN BR0: TX -> CONNECT_ACK pd = 8 callref = 0x09
13:53:20: %LINK-3-UPDOWN: Interface Virtual-Access1, changed state to up
13:53:20: Vi1 DDR: Dialer statechange to up
13:53:20: Vi1 DDR: Dialer call has been placed
13:53:20: Vi1 DDR: dialer protocol up.!!!!
Success rate is 80 percent (4/5), round-trip min/avg/max = 36/36/36 ms

debug ppp authentication - New version of PPP debug that allows you to see only the authentication process.

R1#debug ppp authentication
PPP authentication debugging is on
R1#ping 172.12.12.2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.12.12.2, timeout is 2 seconds:

01:16:11: %LINK-3-UPDOWN: Interface BRI0:1, changed state to up
01:16:11: BR0:1 PPP: Using dialer call direction
01:16:11: BR0:1 PPP: Treating connection as a callout
01:16:11: BR0:1 CHAP: O CHALLENGE id 6 len 23 from "R1"
01:16:11: BR0:1 CHAP: I CHALLENGE id 7 len 23 from "R2"
01:16:11: BR0:1 CHAP: O RESPONSE id 7 len 23 from "R1"
01:16:11: BR0:1 CHAP: I SUCCESS id 7 len 4
01:16:11: BR0:1 CHAP: I RESPONSE id 6 len 23 from "R2"
01:16:11: BR0:1 CHAP: O SUCCESS id 6 len 4
01:16:12: %LINK-3-UPDOWN: Interface Virtual-Access1, changed state to up.!!!!
Success rate is 80 percent (4/5), round-trip min/avg/max = 36/36/36 ms
R1#
01:16:12: Vi1 PPP: Using dialer call direction
01:16:12: Vi1 PPP: Treating connection as a callout
01:16:12: %LINEPROTO-5-UPDOWN: Line protocol on Interface BRI0:1, changed state
to up
01:16:13: %LINEPROTO-5-UPDOWN: Line protocol on Interface Virtual-Access1, chan
ed state to up

dialer fast-idle, dialer idle-timeout -- dialer fast-idle determines how long the link will stay up in the absence of interesting traffic when a call is waiting; dialer idle-timeout determines how long the link will stay in the absence of interesting traffic.

R2(config)#interface bri0
R2(config-if)#dialer idle-timeout 90
R2(config-if)#dialer fast-idle 45

dialer pool-member -- When multiple physical interfaces are in the same dialer pool, the interface with the highest priority will be selected first for outgoing calls. The priority can be changed with the dialer pool-member priority command. In the following example, interface bri0/1 would be selected to place outgoing calls before bri0/0. The default priority is one.

R5(config)#int bri0/0
R5(config-if)#dialer pool-member 1 priority 100

R5(config)#int bri0/1
R5(config-if)#dialer pool-member 1 priority 200

dialer hold-queue - Creates a queue in which packets are held while the ISDN link is built.

R2(config-if)#dialer hold-queue ?
<0-100> Specify size of output hold queue
<cr>

R2(config-if)#dialer hold-queue 100 ?
timeout Specify length of time data is held while interface is connecting
<cr>

R2(config-if)#dialer hold-queue 100 timeout ?
<1-2147483> Holdq timeout in seconds is this value + enable time

R2(config-if)#dialer hold-queue 100 timeout 5

dialer rotary-group, interface dialer - Used to create rotary groups. The first command goes on the physical interface.

R1(config)#int dialer0
R1(config-if)#ip address 20.1.1.1 255.255.255.0
R1(config-if)#encapsulation ppp
R1(config-if)#ppp authentication chap
R1(config-if)#dialer map ip 20.1.1.2 name R2 5551111 broadcast
R1(config-if)#dialer map ip 20.1.1.3 name R3 5552222 broadcast

R1(config)#int bri0
R1(config-if)#dialer rotary-group 0

R1(config)#int bri1
R1(config-if)#dialer rotary-group 0

dialer map, dialer-list, dialer-group - Used to create dial maps and define interesting traffic.

R1(config)#dialer-list 1 protocol ip permit
R1(config)#interface bri0
R1(config-if)#dialer-group 1
R1(config-if)#dialer map ip 172.12.12.2 name R2 broadcast 8358662

dialer watch-list, dialer watch-group, access-list, dialer map - Used to define routes being watched and configure the router for dialer watch.

R2(config)#dialer watch-list 5 ip 10.1.1.0 255.255.255.0
R2(config)#dialer watch-list 5 ip 1.1.1.1 255.255.255.255

R2(config)#interface bri0
R2(config-if)#dialer watch-group 5

R2(config-if)# dialer map ip 1.1.1.1 255.255.255.255. name R1 5557777 broadcast
R2(config-if)# dialer map ip 10.1.1.0 255.255.255.0 name R1 5557777 broadcast

ip tcp header-compression < passive > -- Compresses the TCP header; using the option passive means that headers will be compressed only if compressed headers have already been received from that destination.

R2(config-if)#ip tcp header-compression ?
passive Compress only for destinations which send compressed headers
<cr>

isdn call interface, isdn disconnect interface -- Allows test calls of ISDN without IP addresses or intereresting traffic. Never close a physical interface to end a call.

R1#isdn call interface bri0 8358662
R1#
03:54:43: BR0 DDR: Attempting to dial 8358662
03:54:43: %LINK-3-UPDOWN: Interface BRI0:1, changed state to up
03:54:44: BR0:1 DDR: dialer protocol up
03:54:45: %LINEPROTO-5-UPDOWN: Line protocol on Interface BRI0:1, changed state
to up
03:54:49: %ISDN-6-CONNECT: Interface BRI0:1 is now connected to 8358662 R2

R1#isdn disconnect interface bri 0 ?
all Disconnect the data call(s) on all b channels
b1 Disconnect the data call on b1 channel
b2 Disconnect the data call on b2 channel

R1#isdn disconnect interface bri 0 all
03:58:36: BR0:1 DDR: disconnecting call
03:58:36: BR0:2 DDR: disconnecting call
03:58:36: %ISDN-6-DISCONNECT: Interface BRI0:1 disconnected from 8358662 R2, c
ll lasted 20 seconds
03:58:36: %LINK-3-UPDOWN: Interface BRI0:1, changed state to down
03:58:36: BR0:1 DDR: disconnecting call
03:58:37: %LINEPROTO-5-UPDOWN: Line protocol on Interface BRI0:1, changed state
to down

ppp authentication pap, ppp pap sent-username, ppp authentication chap -- PPP authentication commands. PAP requires the pap sent-username command.

R2(config-if)#ppp authentication pap

R2(config-if)#ppp pap sent-username R2 password CCIE

More options:

R1(config-if)#ppp authentication pap ?
callback Authenticate remote on callback only
callin Authenticate remote on incoming call only
callout Authenticate remote on outgoing call only
chap Challenge Handshake Authentication Protocol (CHAP)
ms-chap Microsoft Challenge Handshake Authentication Protocol (MS-CHAP)
optional Allow peer to refuse to authenticate
<cr>

Another option:

R1(config-if)#ppp authentication pap chap

R1(config-if)#ppp authentication chap pap

When both PAP and CHAP are named in the ppp authentication command, the first method is suggested by the calling router. Should the peer then refuses the first method or suggests an alternate method, the second method will then be used.

ppp callback request, ppp callback accept, class, dialer map class, dialer callback-secure -- All used as part of PPP callback. These commands are in bold in the following configuration.

Client:

username R1 password CCIE

interface BRI0
ip address 172.12.12.2 255.255.255.0
encapsulation ppp
dialer map ip 172.12.12.1 name R1 broadcast 5557777
dialer-group 1
isdn switch-type basic-ni
ppp callback request
ppp authentication chap

Server:

username R2 password CCIE

interface BRI0
ip address 172.12.12.1 255.255.255.0
encapsulation ppp
dialer callback-secure
dialer map ip 172.12.12.2 name R2 class CALL_R2_BACK broadcast 5558888
dialer-group 1
isdn switch-type basic-ni
ppp callback accept
ppp authentication chap

map-class dialer CALL_R2_BACK
dialer callback-server username

ppp multilink, dialer load-threshold -- Used to configure PPP multilink. Both commands are required.

R1(config)#int bri0
R1(config-if)#ppp multilink
R1(config-if)#dialer load-threshold ?
<1-255> Load threshold to place another call

R1(config-if)#dialer load-threshold 191 ?
either Threshold decision based on max of inbound and outbound traffic
inbound Threshold decision based on inbound traffic only
outbound Threshold decision based on outbound traffic only
<cr>

To your success,

Chris Bryant

CCIE #12933

chris@thebryantadvantage.com

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