.
The show ppp multi, show isdn status, and show interface bri commands on RouterB will display similar output with respect to what we just examined on RouterA.
After the idle timeout period (90 seconds without interesting traffic), the call will disconnect. The following screen print shows the call being brought down and both B channels on the BRI (bri 0/0:1 and bri 0/0:2) being changed to a down state.
%LINEPROTO−5−UPDOWN: Line protocol on Interface Virtual−Access1, changed state to down
%LINK−3−UPDOWN: Interface Virtual−Access 1, changed state to down
%ISDN−6−DISCONNECT: Interface BRI0/0:1 disconnected from 8995201 RouterB, call lasted 99 seconds
%ISDN−6−DISCONNECT: Interface BRI0/0:2 disconnected from 8995201 RouterB, call lasted 96 seconds
%LINK−3−UPDOWN: Interface BRI0/0:1, changed state to down
%LINK−3−UPDOWN: Interface BRI0/0:2, changed state to down
%LINEPROTO−5−UPDOWN: Line protocol on Interface BRI0/0:1, changed state to down
%LINEPROTO−5−UPDOWN: Line protocol on Interface BRI0/0:2, changed state to down
Lab #3: Backup Interfaces
Equipment Needed
The following equipment is needed to perform this lab exercise:
Two Cisco routers, each of which must have a single ISDN BRI interface, a single serial interface, and an Ethernet interface
•
Two ISDN BRI circuits
•
Cisco IOS 11.2 or higher
•
A Cisco DCE/DTE V.35 crossover cable. If a crossover cable is not available, you can use a Cisco DCE cable connected to a Cisco DTE cable.
•
A PC running a terminal emulation program for console port connection on the routers
•
Configuration Overview
This configuration demonstrates how to use a backup interface for ISDN dial backup. A backup interface is a designated interface that remains in standby mode until the primary interface goes down. A backup interface
can be either an ISDN interface or a serial interface such as a V.35 port. When a V.35 port acts as a backup interface, the V.35 port is usually connected to an external ISDN terminal adapter or analog modem.
The two routers are connected as shown in Figure 3−14. RouterA and RouterB are connected to an Adtran Atlas 800 ISDN switch. When the serial connection between RouterA and RouterB is broken, RouterA will dial RouterB over the BRI circuit.
Figure 3−14: Backup interfaces
A PC running a terminal emulation program should be connected to the console port of one of the routers using a Cisco rolled cable.
Note An item to keep in mind during this lab exercise is that a drawback of backup interfaces is their testability. The only way to initiate a call from a backup interface is to bring down the primary circuit, thus affecting the customer's traffic. We will see in the next chapter, on floating static routes, that floating statics allow the ISDN interface to be tested while customer traffic continues to flow.
Note The s0/0 interface on RouterA is configured as a DCE interface and supplies clocking to the s0/0 interface of RouterB.
ISDN Switch Setup
If you do not have access to actual ISDN circuits, you can use an ISDN desktop switch. Information on configuring an ISDN desktop switch can be found in the ISDN switch configuration section earlier in this chapter.
Router Configuration
The configurations for the two routers in this example are as follows. ISDN commands are highlighted in bold.
RouterA
RouterA#show run
Building configuration...
Current configuration:
!
version 11.2
no service udp−small−servers no service tcp−small−servers
!
hostname RouterA
!
enable password cisco
!
username RouterB password 7 070C285F4D06
isdn switch−type basic−ni1 ← Set D channel call control
!
interface Ethernet0/0
ip address 195.1.1.1 255.255.255.0
no keepalive
!
interface Serial0/0
backup delay 5 20 ← Go to backup 5 seconds after loss, return 20 seconds after primary returns
backup interface BRI0/0 ← The BRI interface is the backup interface ip address 193.1.1.1 255.255.255.0
isdn spid1 5101 8995101 ← Set SPIDs for both B channels isdn spid2 5102 8995102
dialer idle−timeout 90 ← Disconnect 90 seconds after no interesting packets dialer map ip 196.1.1.2 name RouterB broadcast 8995201 ← Define next hop address and dial string
dialer load−threshold 1 ← Set threshold for adding additional B channels dialer−group 1 ← Associate interface with dialer−list 1
no fair−queue
ppp authentication chap
ppp multilink ← Type to negotiate a multilink PPP session
!
dialer−list 1 protocol ip permit ← Define interesting traffic
!
isdn switch−type basic−ni1 ← Set D channel call control
!
ip address 193.1.1.2 255.255.255.0
isdn spid1 5201 8995201 ← Set the SPID value for both B channels isdn spid2 5202 8995202
dialer idle−timeout 90 ← Set the interesting traffic timeout
dialer map ip 196.1.1.1 name RouterA broadcast ← Define a next hop address dialer−group 1 ← Associate this interface with dialer−list 1
no fair−queue
dialer−list 1 protocol ip permit ← Define interesting traffic
!
Let's start by connecting to RouterA. Verify that interface s 0/0 is in an up/up state. Notice that interface bri 0/0 is designated as the backup interface for s 0/0.
RouterA#show interface s 0/0
Serial0/0 is up, line protocol is up Hardware is QUICC Serial
Internet address is 193.1.1.1/24
Backup interface BRI0/0, kickin load not set, kickout load not set failure delay 5 sec, secondary disable delay 20 sec
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255 Encapsulation PPP, loopback not set, keepalive set (10 sec)
LCP Open
Open: IPCP, CDP
Last input 00:00:08, output 00:00:08, output hang never Last clearing of "show interface" counters never
Input queue: 0/75/0 (size/max/drops); Total output drops: 0 Queueing strategy: weighted fair
Output queue: 0/64/0 (size/threshold/drops) Conversations 0/1 (active/max active)
Reserved Conversations 0/0 (allocated/max allocated) 5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec 489 packets input, 63338 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 1 giants, 0 throttles
4 input errors, 1 CRC, 2 frame, 0 overrun, 0 ignored, 1 abort 518 packets output, 51626 bytes, 0 underruns
0 output errors, 0 collisions, 40 interface resets 0 output buffer failures, 0 output buffers swapped out 8 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up
We see that routes to RouterB are being learned from RIP via s 0/0 on RouterA.
RouterA#show ip route
Codes: C − connected, S − static, I − IGRP, R − RIP, M − mobile, B − BGP D − EIGRP, EX − EIGRP external, O − OSPF, IA − OSPF inter area N1 − OSPF NSSA external type 1, N2 − OSPF NSSA external type 2 E1 − OSPF external type 1, E2 − OSPF external type 2, E − EGP
i − IS−IS, L1 − IS−IS level−1, L2 − IS−IS level−2, * − candidate default U − per−user static route, o − ODR
Gateway of last resort is not set
193.1.1.0/24 is variably subnetted, 2 subnets, 2 masks C 193.1.1.0/24 is directly connected, Serial0/0 C 193.1.1.2/32 is directly connected, Serial0/0 C 195.1.1.0/24 is directly connected, Ethernet0/0
R 196.1.1.0/24 [120/1] via 193.1.1.2, 00:00:05, Serial0/0 R 197.1.1.0/24 [120/1] via 193.1.1.2, 00:00:05, Serial0/0
Type show interface bri 0/0 to display the BRI interface status. Notice that the interface is in a standby mode.
The BRI interface in our previous labs was in an up/up (spoofing) condition. A backup interface is treated differently and stays in standby mode until a call is made.
RouterA#show interface bri 0/0
BRI0/0 is standby mode, line protocol is down Hardware is QUICC BRI with U interface Internet address is 196.1.1.1/24
MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec, rely 255/255, load 1/255 Encapsulation PPP, loopback not set
. .
Make sure that you can ping the far−end router (RouterB) at IP address 193.1.1.2 by using the ping 193.1.1.2 command.
RouterA#ping 193.1.1.2
Type escape sequence to abort.
Sending 5, 100−byte ICMP Echos to 193.1.1.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round−trip min/avg/max = 28/30/32 ms
Now let's connect to RouterB. We see that RouterB has learned a route to the 195.1.1.0 network (RouterA) via interface S0/0.
RouterB#show ip route
Codes: C − connected, S − static, I − IGRP, R − RIP, M − mobile, B − BGP D − EIGRP, EX − EIGRP external, O − OSPF, IA − OSPF inter area N1 − OSPF NSSA external type 1, N2 − OSPF NSSA external type 2 E1 − OSPF external type 1, E2 − OSPF external type 2, E − EGP
i − IS−IS, L1 − IS−IS level−1, L2 − IS−IS level−2, * − candidate default U − per−user static route, o − ODR
Gateway of last resort is not set
193.1.1.0/24 is variably subnetted, 2 subnets, 2 masks C 193.1.1.1/32 is directly connected, Serial0/0 C 193.1.1.0/24 is directly connected, Serial0/0
R 195.1.1.0/24 [120/1] via 193.1.1.1, 00:00:02, Serial0/0 C 196.1.1.0/24 is directly connected, BRI0/0
C 197.1.1.0/24 is directly connected, Ethernet0/0
Make sure that S 0/0 is in an up/up state by entering the show interface s 0/0 command.
RouterB#show interface s 0/0
Serial0/0 is up, line protocol is up
Hardware is QUICC Serial
Internet address is 193.1.1.2/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255 Encapsulation PPP, loopback not set, keepalive set (10 sec)
LCP Open
Open: IPCP, CDP .
.
We see that the BRI interface on RouterB is in an up/up (spoofing) state. Recall that the BRI interface on RouterA is in a standby mode because RouterA is using a backup interface.
RouterB#show interface bri 0/0
BRI0/0 is up, line protocol is up (spoofing) ← D channel is active Hardware is QUICC BRI with U interface
Internet address is 196.1.1.2/24
MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec, rely 255/255, load 1/255 Encapsulation PPP, loopback not set
. .
Now let's reconnect to RouterA. Turn on ISDN call control debugging with the debug isdn q931 command.
RouterA#debug isdn q931
ISDN Q931 packets debugging is on
Turn on PPP authentication tracing with the debug ppp authen command.
RouterA#debug ppp authen
PPP authentication debugging is on
You can check which debug commands are enabled with the show debug command.
RouterA#show debug PPP:
PPP authentication debugging is on ISDN:
ISDN Q931 packets debugging is on
Now we are going to start a ping between RouterA and RouterB. While the ping is running we will pull the serial cable out of interface S0/0 of RouterA. This will cause RouterA to activate the backup interface (bri0/0). Start an extended ping as shown below. The IP address that we will ping is 197.1.1.1, which is the Ethernet interface on RouterB. When the ping begins, the traffic will flow between RouterA and RouterB over the serial interface connecting the two routers. When the serial interface connection is broken, the traffic will start to flow over the ISDN interface.
RouterA#ping Protocol [ip]:
Target IP address: 197.1.1.1 Repeat count [5]: 100000 Datagram size [100]:
Timeout in seconds [2]:
Extended commands [n]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 100000, 100−byte ICMP Echos to 197.1.1.1, timeout is 2 seconds:
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!... ← Pull the cable
%LINEPROTO−5−UPDOWN: Line protocol on Interface Serial0/0, changed state to down ← The serial interface will be declared down
%LINK−3−UPDOWN: Interface Serial0/0, changed state to down
%LINK−3−UPDOWN: Interface BRI0/0:1, changed state to down
%LINK−3−UPDOWN: Interface BRI0/0:2, changed state to down
%LINK−3−UPDOWN: Interface BRI0/0, changed state to up ← The backup interface is activated
Following is the ISDN Q931 call control and CHAP authentication that takes place between RouterA and RouterB when a call is made.
%LINK−3−UPDOWN: Interface BRI0/0:1, changed state to up PPP BRI0/0:1: treating connection as a callout
ISDN BR0/0: TX −> CONNECT_ACK pd = 8 callref = 0x0E
PPP BRI0/0:1: Send CHAP Challenge id=7 ← CHAP Challenge B channel #1 PPP BRI0/0:1: CHAP Challenge id=7 received from RouterB
PPP BRI0/0:1: Send CHAP Response id=7
PPP BRI0/0:1: CHAP response received from RouterB PPP BRI0/0:1: CHAP Response id=7 received from RouterB
PPP BRI0/0:1: Send CHAP Success id=7 ← CHAP passed on B channel #1 PPP BRI0/0:1: remote passed CHAP authentication.
PPP BRI0/0 1: Passed CHAP authentication with remote
%LINK−3−UPDOWN: Interface Virtual−Access1, changed state to up PPP Virtual−Access1: treating connection as a callin
%LINEPROTO−5−UPDOWN: Line protocol on Interface BRI0/0:1, changed state to up
%LINEPROTO−5−UPDOWN: Line protocol on Interface Virtual−Access1, changed state to up
%ISDN−6−CONNECT: Interface BRI0/0:1 is now connected to 8995201 RouterB
ISDN BR0/0: Event: incoming ces value = 2
ISDN BR0/0: TX −> INFORMATION pd = 8 callref = (null)
ISDN BR0/0: Event: incoming ces value = 2
ISDN BR0/0: RX <− CONNECT pd = 8 callref = 0x8F Channel ID i = 0x8A
ISDN BR0/0: Event: incoming ces value = 2
%LINK−3−UPDOWN: Interface BRI0/0:2, changed state to up PPP BRI0/0:2: treating connection as a callout
ISDN BR0/0: TX −> CONNECT_ACK pd = 8 callref = 0x0F
PPP BRI0/0:2: Send CHAP Challenge id=7 ← CHAP Challenge for B channel #2 PPP BRI0/0:2: CHAP Challenge id=7 received from RouterB
PPP BRI0/0:2: Send CHAP Response id=7
PPP BRI0/0:2: CHAP response received from RouterB PPP BRI0/0:2: CHAP Response id=7 received from RouterB
PPP BRI0/0:2: Send CHAP Success id=7 ← CHAP passed on B channel #2 PPP BRI0/0:2: remote passed CHAP authentication
PPP BRI0/0:2: Passed CHAP authentication with remote
%LINEPROTO−5−UPDOWN: Line protocol on Interface BRI0/0:2, changed state to up
%ISDN−6−CONNECT: Interface BRI0/0:2 is now connected to 8995201 RouterB
Once the backup interface is active, the pings will start to work again.
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Success rate is 98 percent (1594/1619), round−trip min/avg/max = 20/24/40 ms
When the ping has completed, type the show isdn status command to display the call status for the router's BRI interface. Notice that there are two active layer 3 calls. This is the two B channels that are now
connected.
RouterA#show isdn status
The current ISDN Switchtype = basic−ni1 ISDN BRI0/0 interface
Layer 1 Status:
ACTIVE
Layer 2 Status:
TEI = 64, State = MULTIPLE_FRAME_ESTABLISHED TEI = 65, State = MULTIPLE_FRAME_ESTABLISHED Spid Status:
TEI 64, ces = 1, state = 5(init)
spid1 configured, spid1 sent, spid1 valid Endpoint ID Info: epsf = 0, usid = 70, tid = 1 TEI 65, ces = 2, state = 5(init)
spid2 configured, spid2 sent, spid2 valid Endpoint ID Info: epsf = 0, usid = 70, tid = 2 Layer 3 Status:
2 Active Layer 3 Call(s) Activated dsl 0 CCBs = 2
CCB:callid=8011, sapi=0, ces=1, B−chan=1 CCB:callid=8013, sapi=0, ces=2, B−chan=2 Total Allocated ISDN CCBs = 2
Type the show ppp multilink command to verify that the two connected B channels on the BRI have been bundled together into an MLPPP bundle. We see from the command's output that both channels bri 0/0:1 and bri 0/0:2 are connected in an MLPPP bundle.
RouterA#show ppp multi
Bundle RouterB, 2 members, Master link is Virtual−Access1 Dialer Interface is BRI0/0
0 lost fragments, 11 reordered, 0 unassigned, sequence 0x99F/0x9A1 rcvd/sent 0 discarded, 0 lost received, 29/255 load
Member Links: 2 BRI0/0:1
BRI0/0:2
Type the show dialer command to display statistics on the current ISDN call. Notice that the second B channel was brought up due to a multilink overload.
RouterA#show dialer
BRI0/0 − dialer type = ISDN
Dial String Successes Failures Last called Last status 8995201 14 5 00:00:37 successful 0 incoming call(s) have been screened.
BRI0/0=:1 − dialer type = ISDN
Idle timer (90 secs), Fast idle timer (20 secs) Wait for carrier (30 secs), Re−enable (15 secs) Dialer state is physical layer up
Idle timer (90 secs), Fast idle timer (20 secs) Wait for carrier (30 secs), Re−enable (15 secs) Dialer state is physical layer up
Dial reason: Multilink bundle overloaded ← Dialer load threshold
statement determines when another channel should be brought up Time until disconnect 50 secs
Current call connected 00:00:39 Connected to 8995201 (RouterB)
Both of the B channels on the BRI will now be in an up/up state. Display the B−channel status with the show interface bri 0/0:1 and show interface bri 0/0:2 commands.
RouterA#show interface bri 0/0:1
BRI0/0:1 is up, line protocol is up ← B channel #1 Hardware is QUICC BRI with U interface
MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec, rely 255/255, load 19/255 Encapsulation PPP, loopback not set, keepalive set (10 sec)
LCP Open, multilink Open .
.
RouterA#show interface bri 0/0:2
BRI0/0:2 is up, line protocol is up ← B channel #2 Hardware is QUICC BRI with U interface
MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec, rely 255/255, load 15/255 Encapsulation PPP, loopback not set, keepalive set (10 sec)
LCP Open, multilink Open .
.
Interface s0/0 is now in a down/down state. It was this interface going down that caused the backup interface, bri0/0, to go into an active state and dial the far−end router.
RouterA#show interface s 0/0
Serial0/0 is down, line protocol is down Hardware is QUICC Serial
Internet address is 193.1.1.1/24
Backup interface BRI0/0, kickin load not set, kickout load not set failure delay 5 sec, secondary disable delay 20 sec
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255 Encapsulation PPP, loopback not set, keepalive set (10 sec)
LCP Closed
Closed: IPCP, CDP
Last input 00:02:20, output 00:02:20, output hang never Last clearing of "show interface" counters never
Input queue: 0/75 /0 (size/max/drops); Total output drops: 0 Queueing strategy: weighted fair
Output queue: 0/64 /0 (size/threshold/drops) Conversations 0/1 (active/max active)
Reserved Conversations 0/0 (allocated/max allocated) 5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec 1075 packets input, 120020 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 1 giants, 0 throttles
5 input errors, 1 CRC, 3 frame, 0 overrun, 0 ignored, 1 abort 1113 packets output, 100942 bytes, 0 underruns
0 output errors, 0 collisions, 45 interface resets
0 output buffer failures, 0 output buffers swapped out 11 carrier transitions
DCD=up DSR=up DTR=down RTS=down CTS=up
Let's examine the routing table with the show ip route command. Notice that we have now learned a RIP route to the 197.1.1.0 network via 196.1.1.2. 197.1.1.0 is the Ethernet network on RouterB. 196.1.1.2 is the IP address of the BRI interface on RouterB. Our routing table now reflects the fact that our primary serial interface, s0/0, is down and our backup interface, bri0/0, is now our only connection to RouterB. Routes learned via s0/0 will be deleted as soon as that interface goes down.
RouterA#show ip route
Codes: C − connected, S − static, I − IGRP, R − RIP, M − mobile, B − BGP D − EIGRP, EX − EIGRP external, O − OSPF, IA − OSPF inter area N1 − OSPF NSSA external type 1, N2 − OSPF NSSA external type 2 E1 − OSPF external type 1, E2 − OSPF external type 2, E − EGP
i − IS−IS, L1 − IS−IS level−1, L2 − IS−IS level−2, * − candidate default U − per−user static route, o − ODR
Gateway of last resort is not set
C 195.1.1.0/24 is directly connected, Ethernet0/0 196.1.1.0/24 is variably subnetted, 2 subnets, 2 masks C 196.1.1.0/24 is directly connected, BRI0/0
C 196.1.1.2/32 is directly connected, BRI0/0 R 197.1.1.0/24 [120/1] via 196.1.1.2, 00:00:05, BRI0/0
Now we are going to start a ping and reconnect our serial cable to RouterB. Recall from the configuration of RouterA that the backup interface will activate 5 seconds after S0/0 goes down and will go inactive 20 seconds after S0/0 becomes active again.