Case Study: ISDN Configuration Problem

This case study explores a problem that involves setting up IS-IS routing over an ISDN link. The objective is to put the troubleshooting knowledge acquired in this chapter to immediate use by trying to figure out any potential problems in the setup.

RTA and RTB are connected over an ISDN link, as shown in Figure 11-12. Standard configuration is employed, as demonstrated in Example 11-39.

Figure 11-12. Network Topology for ISDN Configuration Problem

Example 11-39 Configurations for RTA and RTB in Figure 11-12

 RTA#  interface BRI1/0   ip address 192.168.31.1 255.255.255.0    ip router isis    encapsulation ppp   bandwidth 56000   isdn spid1 91947209980101 4720998   isdn spid2 91947209990101 4720999   dialer idle-timeout 1200    dialer map clns 49.0040.0000.0000.3200.00 name RTB broadcast 4723074     dialer map ip 192.168.31.3 name RTB broadcast 4723074    dialer hold-queue 10   dialer load-threshold 100   dialer-group 1   ppp authentication chap    clns router isis    !    router isis    passive-interface Loopback0   net 49.0040.0000.0000.3100.00   is-type level-1   !    clns route 49.0040.0000.0000.3200.00 BRI1/0     dialer-list 1 protocol ip permit     dialer-list 1 protocol clns permit   _____________________________________________________________________________________ RTB#  interface BRI1/0   ip address 192.168.31.3 255.255.255.0    ip router isis    encapsulation ppp   bandwidth 56000   isdn spid1 91947230740101 4723074   isdn spid2 91947230750101 4723075   dialer idle-timeout 1200    dialer map clns 49.0040.0000.0000.3100.00 name RTA broadcast 4720998     dialer map ip 192.168.31.1 name RTA broadcast 4720998    dialer hold-queue 20   dialer load-threshold 200   dialer-group 1   ppp authentication chap    clns router isis     router isis    passive-interface Loopback0   net 49.0040.0000.0000.3200.00   is-type level-1   !    clns route 49.0040.0000.0000.3100.00 BRI1/0     dialer-list 1 protocol ip permit    dialer-list 1 protocol clns permit  

In the configurations in Example 11-39, the dialer-list command is used to specify "interesting" packets, which could force a connection setup and bring up the ISDN link. Both ip and clns keywords are specified on either side of the link; however, as shown in Example 11-40 and the corresponding debugs in Example 11-41, using CLNS ping from RTB cannot bring up the circuit.

Example 11-40 Attempting to Bring Up the ISDN Connection with CLNS ping from RTB

 RTB#  ping clns 49.0040.0000.0000.3100.00  Type escape sequence to abort. Sending 5, 100-byte CLNS Echos with timeout 2 seconds CLNS: cannot send ECHO. CLNS: cannot send ECHO. CLNS: cannot send ECHO. CLNS: cannot send ECHO. CLNS: cannot send ECHO. Success rate is 0 percent (0/5) 

Example 11-41 shows how debugging of CLNs packets determines the root cause of the problem. The highlighted text indicates encapsulation failure because the BRI interface is an unknown data link type.

Example 11-41 Using debugs clns packets to Troubleshoot the Problem

 RTB#  debug clns packets  CLNS packets debugging is on Aug  9 09:35:17: CLNS: Originating packet, size 100 Aug 9 09:35:17:  from 49.0040.0000.0000.3200.00   to 49.0040.0000.0000.3100.00  via 49.0040.0000.0000.3100.00  (BRI1/0 **Unknown SNPA type**)  Aug  9 09:35:17:  CLNS encaps failed on BRI1/0 for dst= 49.0040.0000.0000.3100.00  Aug  9 09:35:17: CLNS: Originating packet, size 100 Aug  9 09:35:17:       from 49.0040.0000.0000.3200.00       to 49.0040.0000.0000.3100.00       via 49.0040.0000.0000.3100.00 (BRI1/0 **Unknown SNPA type**) Aug  9 09:35:17: CLNS encaps failed on BRI1/0 for dst= 49.0040.0000.0000.3100.00 Aug  9 09:35:17: CLNS: Originating packet, size 100 Aug  9 09:35:17:       from 49.0040.0000.0000.3200.00       to 49.0040.0000.0000.3100.00       via 49.0040.0000.0000.3100.00 (BRI1/0 **Unknown SNPA type**) Aug  9 09:35:17: CLNS encaps failed on BRI1/0 for dst= 49.0040.0000.0000.3100.00 Aug  9 09:35:17: CLNS: Originating packet, size 100 Aug  9 09:35:17:       from 49.0040.0000.0000.3200.00       to 49.0040.0000.0000.3100.00       via 49.0040.0000.0000.3100.00 (BRI1/0 **Unknown SNPA type**) Aug  9 09:35:17: CLNS encaps failed on BRI1/0 for dst= 49.0040.0000.0000.3100.00 Aug  9 09:35:17: CLNS: Originating packet, size 100 Aug  9 09:35:17:       from 49.0040.0000.0000.3200.00       to 49.0040.0000.0000.3100.00       via 49.0040.0000.0000.3100.00 (BRI1/0 **Unknown SNPA type**) Aug  9 09:35:17: CLNS encaps failed on BRI1/0 for dst= 49.0040.0000.0000.3100.00 

Experimentation with the various options in the dialer-list command, however, confirms that the appropriate keyword required is clns_is instead of clns, as demonstrated in Example 11-42.

Example 11-42 CLNS Related Keyword Options for the dialer-list Command

 RTB(config)#  dialer-list 1 protocol?  clns              OSI Connectionless Network Service   clns_es           CLNS End System   clns_is           CLNS Intermediate System RTB(config)#dialer-list 1 protocol clns_is permit 

Example 11-43 shows that the ping clns can now bring up the links after appropriate change is made in the dialer list configuration.

This case study elaborates how the ping clns command is combined with CLNP packet debugging to troubleshoot a basic connectivity problem.

Example 11-43 Retesting the Connection with the clns is option in the dialer-list statement

 RTB#  ping clns 49.0040.0000.0000.3100.00  Type escape sequence to abort. Sending 5, 100-byte CLNS Echos with timeout 2 seconds !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 40/42/44 ms