Problem Isolation in IS-IS
This section discusses the different commands available in the Cisco IOS to isolate and troubleshoot problems in IS-IS networks. Table 10.3 lists the various show command options for IS-IS networks.
| Command | Description |
|---|---|
| router#show isis | Shows if IS-IS routing protocol is enabled on a specified router. This command also displays the system level information about the IS-IS execution. |
| router#show clns | Provides global CLNS information such as number of interfaces, NET, type of routing (L1, L2, or L1-L2), and routing area ID. |
| router#show clns neighbor | Shows System ID, Interface ID, SNPA, Hold time, IS type, and protocol used. |
| router#show clns interfaceinterface interface- name | Displays details about the CLNS interface where name represents the name of the interface whose details are displayed. |
| router#show clns protocol | Displays details of the CLNS protocol, including the areas involving redistribution details. |
| router#show clns traffic | Displays details about network traffic sequence in a router. |
| router#show isis database level-1 | Displays the Level 1 link-state database. |
| router#show isis database level-2 | Displays the Level 2 link-state database. |
| router#show isis spf-log | Displays time and reason for the shortest path algorithm execution. |
Consider the example depicted in Figure 10.1. The output of commands from Table 10.1 will be discussed with respect to this scenario.
Figure 10.1: A network configured with an IS-IS routing protocol.
Figure 10.1 shows part of an IS-IS network with four routers R1, R2, R3, and R4. R1 and R2 belong to Area 49.0001. R3 and R4 belong to Area 49.0002. R2 connects Area 49.0001 to Area 49.0002. R1 and R4 function as L1 routers, and R2 and R4 are L1-L2 routers.
In Figure 10.1, consider that the show commands are issued at R2. The configuration of R1 is shown in Listing 10.1.
Listing 10.1 Configuration of R1
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Router#enable Router#conf terminal Router(conf)#hostname R1 R1(conf)#Interface Loopback0 R1(conf)#ip address 172.148.1.3 255.255.255.255 ! ! R1(conf)#interface FastEthernet0/0 R1(conf)#ip address 172.148.120.5 255.255.255.0 R1(conf)#ip router isis ! ! R1(conf)#router isis R1(conf)#is-type level-1 R1(conf)#passive-interface Loopback0 R1(conf)#net 49.0001.1721.4800.1003.00
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The configuration of R2 is shown in Listing 10.2.
Listing 10.2 Configuration of R2
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Router#enable Router#conf terminal Router(conf)#hostname R2 R2(conf)#Interface Loopback0 R2(conf)#ip address 172.148.1.4 255.255.255.255 ! ! R2(conf)#Interface Pos2/0/0 R2(conf)#ip address 172.148.222.1 255.255.255.0 R2(conf)#ip router isis R2(conf)#isis circuit-type level-2 ! ! R2(conf)#FastEthernet4/0/0 R2(conf)#ip address 172.148.120.10 255.255.255.0 R2(conf)#ip router isis R2(conf)#isis circuit-type level-1 ! ! R2(conf)#router isis R2(conf)#passive-interface Loopback0 R2(conf)#net 49.0001.1721.4800.1004.00
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The configuration of R3 is shown in Listing 10.3.
Listing 10.3 Configuration of R3
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Router#enable Router#conf terminal Router(conf)#hostname R3 R3(conf)#Interface Loopback0 R3(conf)#ip address 172.148.2.2 255.255.255.255 ! ! R3(conf)#Interface Pos1/0/0 R3(conf)#ip address 172.148.222.2 255.255.255.0 R3(conf)#ip router isis R3(conf)#isis circuit-type level-2 ! R3(conf)#interface Fddi3/0 R3(conf)#ip address 172.148.111.2 255.255.255.0 R3(conf)#ip router isis R3(conf)#isis circuit-type level-1 ! R3(conf)#router isis R3(conf)#passive-interface Loopback0 R3(conf)#net 49.0002.1721.4800.2002.00
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The configuration of R4 is shown in Listing 10.4.
Listing 10.4 Configuration of R4
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Router#enable Router#conf terminal Router(conf)#hostname R4 R4(conf)#Interface Loopback0 R4(conf)#ip address 172.148.2.6 255.255.255.255 ! R4(conf)#interface Fddi6/0 R4(conf)#ip address 172.148.111.4 255.255.255.0 R4(conf)#ip router isis ! R4(conf)#router isis R4(conf)#is-type level-1 R4(conf)#passive-interface Loopback0 R4(conf)#net 49.0002.1721.4800.2006.00
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The output of the show isis command in R2 is shown in Listing 10.5.
Listing 10.5 Output for show isis Command in R2
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R2#show isis Global ISIS information ISIS process tag: R2 System ID: 1721.4800.1004 NET: 49.0001.1721.4800.1004.00 Maximum number of areas: 2 There is 1 manual area address 49 There is 1 active area address 49 ISIS level-1 ISIS is enabled on 2 interfaces Distance : 120 Maximum of 1 path per route Number of SPF runs, L1: 14, L2: 5
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The output of the router#show clns command in R2 is shown in Listing 10.6.
Listing 10.6 Output of router#show clns Command in R2
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R2#show clns Global CLNS Information: 2 Interfaces Enabled for CLNS NET: 49.0001.1721.4800.1004.00 Configuration Timer: 60, Default Holding Timer: 300, Packet Lifetime 64 ERPDU's requested on locally generated packets Intermediate system operation enabled (forwarding allowed) IS-IS level-1-2 Router: Routing for Area: 49.0001
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The output of the router#show clns neighbor command in R2 is shown in Listing 10.7.
Listing 10.7 Output of router#show clns neighbor Command in R2
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R2#show clns neighbors System Id SNPA Interface State Holdtime Type Protocol 1721.4800.2002 *PPP* PO2/0/0 Up 19 L2 IS- IS 1721.4800.1003 00e0.1492.2c00 Fa4/0/0 Up 11 L1 IS- IS
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The output of router#show clns interface interface-name command in R2 is shown in Listing 10.8.
Listing 10.8 Output of router#show clns interface interface-name Command in R2
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R2#show clns interface POS2/0/0 POS2/0/0 is up, line protocol is up Checksums enabled, MTU 4470, Encapsulation PPP ERPDUs enabled, min. interval 10 msec. RDPDUs enabled, min. interval 100 msec. , Addr Mask enabled Congestion Experienced bit set at 4 packets CLNS fast switching disabled CLNS SSE switching disabled DEC compatibility mode OFF for this interface Next ESH/ISH in 47 seconds Routing Protocol: IS-IS Circuit Type: level-1-2 Interface number 0x0, local circuit ID 0x100 Level-1 Metric: 10, Priority: 64, Circuit ID: 1721.4800.2002.00 Number of active level-1 adjacencies: 0 Level-2 Metric: 10, Priority: 64, Circuit ID: 1721.4800.1004.00 Number of active level-2 adjacencies: 1 Next IS-IS Hello in 2 seconds
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The output of router#show clns protocol command in R2 is shown in Listing 10.9.
Listing 10.9 Output of router#show clns protocol Command in R2
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R2#show clns protocol IS-IS Router: <Null Tag> System Id: 1721.4800.1004.00 IS-Type: level-1-2 Manual area address(es): 49.0001 Routing for area address(es): 49.0001 Interfaces supported by IS-IS: FastEthernet4/0/0 - IP POS2/0/0 - IP Redistributing: static Distance: 120
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The output of router#show clns traffic command in R2 is shown in Listing 10.10.
Listing 10.10 Output of router#show clns traffic Command in R2
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R2#show clns traffic CLNS & ESIS Output: 14, Input: 436 CLNS Local: 0, Forward: 0 CLNS Discards: Hdr Syntax: 0, Checksum: 0, Lifetime: 0, Output cngstn: 0 No Route: 0, Dst Unreachable 0, Encaps. Failed: 0 NLP Unknown: 0, Not an IS: 0 CLNS Options: Packets 0, total 0, bad 0, GQOS 0, cngstn exprncd 0 CLNS Segments: Segmented: 0, Failed: 0 CLNS Broadcasts: sent: 0, rcvd: 0 Echos: Rcvd 0 requests, 0 replies Sent 0 requests, 0 replies ESIS(sent/rcvd): ESHs: 0/0, ISHs: 14/15, RDs: 0/0, QCF: 0/0 ISO-IGRP: Querys (sent/rcvd): 0/0 Updates (sent/rcvd): 0/0 ISO-IGRP: Router Hellos: (sent/rcvd): 0/0 ISO-IGRP Syntax Errors: 0 IS-IS: Level-1 Hellos (sent/rcvd): 84/244 IS-IS: Level-2 Hellos (sent/rcvd): 0/0 IS-IS: PTP Hellos (sent/rcvd): 84/82 IS-IS: Level-1 LSPs sourced (new/refresh): 7/1 IS-IS: Level-2 LSPs sourced (new/refresh): 5/0 IS-IS: Level-1 LSPs flooded (sent/rcvd): 5/5 IS-IS: Level-2 LSPs flooded (sent/rcvd): 1/6 IS-IS: LSP Retransmissions: 0 IS-IS: Level-1 CSNPs (sent/rcvd): 0/82 IS-IS: Level-2 CSNPs (sent/rcvd): 1/1 IS-IS: Level-1 PSNPs (sent/rcvd): 1/0 IS-IS: Level-2 PSNPs (sent/rcvd): 3/1 IS-IS: Level-1 DR Elections: 2 IS-IS: Level-2 DR Elections: 1 IS-IS: Level-1 SPF Calculations: 3 IS-IS: Level-2 SPF Calculations: 3 IS-IS: Level-1 Partial Route Calculations: 0 IS-IS: Level-2 Partial Route Calculations: 0 IS-IS: LSP checksum errors received: 0 IS-IS: Update process queue depth: 0/200 IS-IS: Update process packets dropped: 0
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The output of router#show isis database command in R2 is shown in Listing 10.11.
Listing 10.11 Output of router#show isis database Command in R2
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R2#show isis database IS-IS Level-1 Link State Database LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL 1721.4800.1004.00-00* 0x00000019 0x2783 1153 1/0/0 (11) 1721.4800.1003.00-00 0x0000000C 0x2179 905 0/0/0 (5) 1721.4800.1003.01-00 0x00000009 0x40EC 831 0/0/0 (4) IS-IS Level-2 Link State Database LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL 1721.4800.1004.00-00* 0x00000010 0xFC45 1153 0/0/0 (9) 1721.4800.1004.01-00* 0x00000001 0x4CB7 1137 0/0/0 (10) 1721.4800.2002.00-00 0x00000018 0x86A6 1141 0/0/0 (3) 1721.4800.2002.02-00 0x00000004 0x8558 881 0/0/0 (2) R2> sh isis database 1721.4800.1004.00-00 detail IS-IS Level-1 LSP 1721.4800.1004.00-00 LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL 1721.4800.1004.00-00* 0x00000006 0x4D70 991 1/0/0 (1) Area Address: 49.0001 NLPID: 0xCC IP Address: 172.148.120.10 Metric: 10 IP 172.148.222.0 255.255.255.0 Metric: 10 IP 172.148.120.0 255.255.255.0 Metric: 0 IP 172.148.1.4 255.255.255.255 Metric: 10 IS 1721.4800.1003.01 Metric: 0 ES 1721.4800.1004 IS-IS Level-2 LSP 1721.4800.1004.00-00 LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL 1721.4800.1004.00-00* 0x00000004 0x1539 980 0/0/0 (2) Area Address: 49.0001 NLPID: 0xCC IP Address: 172.148.222.1 Metric: 10 IS 1721.4800.1004.01 Metric: 10 IS 1721.4800.2002.00 Metric: 10 IP 172.148.120.0 255.255.255.0 Metric: 0 IP 172.148.1.4 255.255.255.255 Metric: 10 IP 172.148.1.3 255.255.255.255 Metric: 10 IP 172.148.222.0 255.255.255.0
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The output of router#show isis spf-log command in R2 is shown in Listing 10.12.
Listing 10.12 Output of router#show isis spf-log Command in R2
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R2#show isis spf-log Level 1 SPF log When Duration Nodes Count Last trigger LSP Triggers 00:05:30 0 1 6 1721.4800.1004.00-00 NEWAREA RTCLEARED NEWADJ NEWLSP TLVCONTENT 00:05:20 0 3 3 1721.4800.1003.01-00 NEWADJ TLVCONTENT 00:05:05 0 3 2 1721.4800.1004.00-00 ATTACHFLAG LSPHEADER Level 2 SPF log When Duration Nodes Count Last trigger LSP Triggers 00:05:31 0 1 2 1721.4800.1004.00-00 RTCLEARED NEWLSP 00:05:21 0 1 3 1721.4800.1004.00-00 NEWADJ TLVCODE TLVCONTENT 00:05:11 0 2 1 1721.4800.2002.00-00 LSPHEADER
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Table 10.4 shows the different debug commands that can be used for the thorough troubleshooting of problems in IS-IS networks.
| Command | Description |
|---|---|
| debug isis adj-packets | Enables IS-IS adjacency packets and displays IS-IS packet information. |
| debug isis spf-events | Enables debugging in the Shortest Path Function (SPF) events. |
| debug isis snp-packets | Enables and displays CSNP/PSNP packets information. |
| Debug isis spf-update | Shows SPF updated information. |
Consider the example depicted in Figure 10.1. The output of commands from Table 10.4 will be discussed with respect to this scenario.
The output of debug isis adj-packets command in R2 is shown in Listing 10.13.
Listing 10.13 Output of debug isis adj-packets Command in R2
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R2#debug isis adj-packets ISIS-Adj: Rec L1 IIH from 00e0.1492.2c00 (FastEthernet4/0/0), cir type 1, cir id 1721.4800.1003.01 ISIS-Adj: Sending L1 IIH on FastEthernet4/0/0 ISIS-Adj: Rec L1 IIH from 00e0.1492.2c00 (FastEthernet4/0/0), cir type 1, cir id 1721.4800.1003.01 ISIS-Adj: Sending serial IIH on POS2/0/0 ISIS-Adj: Rec serial IIH from *PPP* on POS2/0/0, cir type 3, cir id 00
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The output of the debug isis spf-events command in R2 is shown in Listing 10.14.
Listing 10.14 Output of debug isis spf-events Command in R2
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R2#debug isis spf-events ISIS-SPF: Compute L1 SPT ISIS-SPF: Move 1721.4800.1004.00-00 to PATHS, metric 0 ISIS-SPF: thru 2147483647/2147483647/2147483647, delay 0/0/0, mtu 2147483647/2147483647/2147483647, hops 0/0/0, ticks 0/0/0 ISIS-SPF: Add 1721.4800.1003.01-00 to TENT, metric 10 ISIS-SPF: Next hop local ISIS-SPF: Move 1721.4800.1003.01-00 to PATHS, metric 10 ISIS-SPF: thru 2147483647/2147483647/2147483647, delay 0/0/0, mtu 2147483647/2147483647/2147483647, hops 0/0/0, ticks 0/0/0 ISIS-SPF: considering adj to 1721.4800.1003 (FastEthernet4/0/0) metric 10 ISIS-SPF: (accepted) ISIS-SPF: Add 1721.4800.1003.00-00 to TENT, metric 10 ISIS-SPF: Next hop 1721.4800.1003 (FastEthernet4/0/0) ISIS-SPF: Move 1721.4800.1003.00-00 to PATHS, metric 10 ISIS-SPF: Add 172.148.120.0/255.255.255.0 to IP route table, metric 20 ISIS-SPF: Next hop 1721.4800.1003/172.148.120.5 (FastEthernet4/0/0) (rejected) ISIS-SPF: Add 172.148.1.3/255.255.255.255 to IP route table, metric 10 ISIS-SPF: Next hop 1721.4800.1003/172.148.120.5 (FastEthernet4/0/0) (accepted) ISIS-SPF: Add 144.254.0.0/255.255.0.0 to IP route table, metric 60 ISIS-SPF: Next hop 1721.4800.1003/172.148.120.5 (FastEthernet4/0/0) (rejected)
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The output of the debug isis snp-packets command in R2 is shown in Listing 10.15.
Listing 10.15 Output of debug isis snp-packets Command in R2
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R2#debug isis snp-packets ISIS-SNP: Rec L1 CSNP from 1721.4800.1003 (FastEthernet4/0/0) ISIS-SNP: CSNP range 0000.0000.0000.00-00 to FFFF.FFFF.FFFF.FF-FF ISIS-SNP: Same entry 1721.4800.1004.00-00, seq 92 ISIS-SNP: Same entry 1721.4800.1003.00-00, seq 79 ISIS-SNP: Same entry 1721.4800.1003.01-00, seq 77 Area 49.0001 Area 49.0002
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The output of debug isis spf-update command in R2 is shown in Listing 10.16.
Listing 10.16 Output of debug isis spf-update Command in R2
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R2( config )# int fa4/0/0 R2( config -if)#isis metric 13 R2( config -if)#^Z R2# ISIS-SPF-TRIG: L1, new metric ISIS-Update: Building L1 LSP ISIS-Update: TLV contents different, code 80 ISIS-Update: TLV contents different, code 2 ISIS-SPF-TRIG: L1, 1721.4800.1004.00-00 TLV contents changed, code 2 ISIS-Update: Full SPF required ISIS-Update: Sending L1 LSP 1721.4800.1004.00-00, seq 96, ht 1199 on FastEthernet4/0/0 ISIS-SNP: Rec L1 CSNP from 1721.4800.1003 (FastEthernet4/0/0) ISIS-Stats : Compute L1 SPT ISIS-Stats : Complete L1 SPT, Compute time 0.000, 3 nodes, 2 links on SPT, 0 suspends ISIS-Update: Building L2 LSP ISIS-Update: TLV contents different, code 80 ISIS-Update: TLV contents different, code 80 ISIS-Update: Leaf routes changed ISIS-Update: Sending L2 LSP 1721.4800.1004.00-00, seq 96, ht 1199 on POS2/0/0 ISIS-Update: Building L2 LSP ISIS-Update: Rate limiting L2 LSP 1721.4800.1004.00-00, seq 97 ISIS-Update: TLV contents different, code 80 ISIS-Update: TLV contents different, code 80 ISIS-Update: Leaf routes changed ISIS-Update: Sending L2 LSP 1721.4800.1004.00-00, seq 97, ht 1196 on POS2/0/0
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