Basic Configuration of Integrated IS-IS The preparation for configuring any routing protocol requires a thorough understanding of the network topology and a coherent addressing scheme. When you have these, the basic configuration of Integrated IS-IS is as follows : - Step 1. Enable the routing process Integrated IS-IS with the router isis command.
- Step 2. Configure the Network Entity Title (NET) address, thus assigning the area with the net network-address router subcommand.
- Step 3. Enable Integrated IS-IS for IP on the relevant interfaces with the ip router isis interface subcommand.
Figure 12-1 illustrates a simple network to support the working configuration example. The figure shows the topology of the network and the addressing scheme that was used. Figure 12-1. Basic Integrated IS-IS Configuration  Example 12-1 shows the basic configuration required to run Integrated IS-IS. The relevant commands are highlighted for easy identification, and a brief explanation of the code is inserted after an exclamation mark to make the code easier to read. Note that the router process is started and the NET address is defined immediately beneath this router process. This is done because the IS-IS address is assigned to the router and, as such, is a part of the routing process. IS-IS is started on the interface after the IS-IS router process is defined with a NET address. Example 12-1. Basic Integrated IS-IS Configuration Working Example for Router A interface Ethernet0 ip address 140.100.96.1 255.255.255.0 !assign the IP address and mask ip router isis !start IS-IS on the interface ! interface Serial0 no ip address encapsulation frame-relay no fair-queue clockrate 56000 ! interface Serial0.1 point-to-point ip address 140.100.64.1 255.255.255.0 !assign the IP address and mask ip router isis !start IS-IS on the interface frame-relay interface-dlci 629 ! interface Serial0.2 point-to-point ip address 140.100.32.1 255.255.255.0 !assign the IP address and mask ip router isis !start IS-IS on the interface frame-relay interface-dlci 931 ! ! router isis net 49.0001.0000.0000.000a.00 !Start the IS-IS routing process and define the ISO address for the entire router. ! ip classless Remember that by default, Cisco routers are configured as Level 1-2 routers to avoid suboptimal routing. Also, the clns routing command, which turns on the routing process for the OSI protocol stack and allows it to route OSI traffic across the router, is not required for IP-only IS-IS. In some versions of the Cisco IOS software, clns routing is written into the configuration file automatically by Cisco, when the routing process for IS-IS is configured. Optional Integrated IS-IS Commands Though the commands in this section are considered optional, they might or might not be optional in your network. For instance, if you are running Frame Relay, you must carefully consider and implement a configuration of Integrated IS-IS over the nonbroadcast multiaccess (NBMA) cloud. One of many considerations is how to separate the network into areas and which routers are to take which level of responsibility. Changing the Router from Level 1-2 The reason you change the routing level in Integrated IS-IS is to overcome the problem of Integrated IS-IS consuming resources on both the routers and the media. Using the topology in Figure 12-2, it is possible to configure Routers D, E, and F as Level 1 routers because they are internal to their areas. The following syntax shows the command structure: Router(config)# ip router isis Router(config-router)# isis circuit-type level 1 Figure 12-2. Changing the Level of Routing Both for the Entire Router and at the Interface Level  It is also possible to change the level of routing to Level 1 at the interface level by issuing the isis circuit-type level-1 command under the interface. In Figure 12-2, this is done on the Routers A, B, and C. The Ethernet interface pointing to the stub Routers D, E, and F is configured to be running Level 1 routing, whereas the serial interface runs only Level 2 routing. Level 1-2 routers send LSPs with an attached (ATT) bit in their Level 1 LSPs, indicating that they are attached to another area. This creates a default route in the Level 1 router pointing to the nearest Level 2 router. This allows the nearest Level 2 router to be the transit router for all data destined for another area. As illustrated in Figure 12-2, Example 12-2 shows Router A configured as Level 1 on the Ethernet interface pointing to Router D. The other interfaces are configured as Level 2 only. The relevant commands are highlighted for easy identification. Example 12-2. Changing Router A Routing Level on an Interface Basis Working Example for Router A interface Ethernet0 ip address 140.100.96.1 255.255.255.0 ip router isis isis circuit-type level-1 !Configure Level 1 routing on the interface ! interface Serial0 no ip address encapsulation frame-relay no fair-queue ! interface Serial0.1 point-to-point ip address 140.100.64.1 255.255.255.0 ip router isis frame-relay interface-dlci 629 isis circuit-type level-2-only ! Configure Level 2 routing on the interface ! interface Serial0.2 point-to-point ip address 140.100.32.1 255.255.255.0 ip router isis frame-relay interface-dlci 931 isis circuit-type level-2-only !Configure Level 2 routing on the interface ! ! router isis net 49.0001.0000.0000.000a.00 ! ip classless Example 12-3 shows the configuration command to change the level of routing on Router D to be Level 1. Note that this command appears under the router isis command, changing the behavior of the entire process, rather than just the interface level. The relevant commands are highlighted for easy identification. Example 12-3. Changing the Level of Routing for the Entire Router Working Example for Router D interface Ethernet0 ip address 140.100.96.2 255.255.255.0 no ip directed-broadcast ip router isis ! interface Serial0 no ip address no ip directed-broadcast no ip mroute-cache Shutdown no fair-queue ! interface Serial0.1 no ip directed-broadcast ! interface Serial1 no ip address no ip directed-broadcast Shutdown ! ! router isis net 49.0001.0000.0000.000d.00 is-type level-1 !Define the router as a Level 1 router ! ip classless Configuring Summarization Configuring summarization is straightforward. The complexity is in the addressing scheme design. There are three rules to remember about summarizing IP routes for Integrated IS-IS: -
Routes cannot be summarized within an area; that is, the protocol does not allow intra-area summarization. -
Internal routes can be summarized between areas, from a Level 1 to a Level 2 router. Thus, summarization is configured on a Level 1-2 router, which turns the routes from Level 1 routes into Level 2 routes. -
If summarization is used, all the Level 1-2 routers in the area need to be summarizing routes out of the area in the same manner. If one router is advertising the routes that are more specific (unsummarized), all the traffic will be sent to this router in accordance to the longest-match rule. This will result in suboptimal routing and might overwhelm the receiving router. To configure summarization, enter the summary-address command followed by the summary address and mask under the router process. Figure 12-3 shows the topology used to support the working example shown in Example 12-4. Figure 12-3. Summarizing IP Addresses Between IS-IS Areas  In Figure 12-3, the IP routes from Router B are summarized into areas 0001 and 0003. Router B is capable of summarizing routes because the router is both a Level 1 and a Level 2 router, straddling more than one area and forming the connectivity between the areas. This functionality is similar to an ABR in OSPF. Example 12-4 shows Router B summarizing routes 140.100.104.0 through 140.100.107.0 with a mask summarized from /24 to /22. The relevant command is highlighted for easy identification. Example 12-4. Summarization of IP Routes from Router B Working Example for Router B interface Ethernet0 ip address 140.100.104.1 255.255.255.0 no ip directed-broadcast ip router isis isis circuit-type level-1 ! interface Serial0 no ip address no ip directed-broadcast encapsulation frame-relay no ip mroute-cache no fair-queue ! interface Serial0.2 point-to-point ip address 140.100.32.2 255.255.255.0 no ip directed-broadcast ip router isis isis circuit-type level-2-only frame-relay interface-dlci 931 ! interface Serial0.3 point-to-point ip address 140.100.16.2 255.255.255.0 no ip directed-broadcast ip router isis isis circuit-type level-2-only frame-relay interface-dlci 631 ! ! router isis summary-address 140.100.104.0 255.255.252.0 ! Routes 140.100.104.0-140.100.107.0 summarized with the /22 bit mask. net 49.0002.0000.0000.000b.00 ! ip classless Configuring NBMA IS-IS acknowledges only two types of network topologies: broadcast and point-to-point. If the network link is not a serial line connecting to a single router (a point-to-point network), IS-IS automatically defines the link to be broadcast. Because NBMA is neither a point-to-point nor a broadcast medium, the configuration for IS-IS over NBMA deserves a moment's consideration. For multiaccess WAN interfaces (such as ATM, Frame Relay, and X.25), it is highly recommended that you configure the NBMA cloud as multiple point-to-point subinterfaces. This is a simpler design that makes routing much more robust, particularly if one or more permanent virtual circuits (PVCs) in the NBMA cloud fail. An example of an NBMA technology is Frame Relay. It is a WAN technology that is widely used and has evolved beyond the point-to-point capabilities. When configured in a full mesh, the cloud is multiaccess, although each circuit is discrete and therefore not a true broadcast medium. The Broadcast Configuration over NBMA If the NBMA cloud is fully meshed, the IS-IS broadcast option is the configuration to choose. As far as IS-IS is concerned , the NBMA cloud is a broadcast medium, such as Ethernet, and so a DIS router is elected. Decisions about manually determining which router is elected should be made in reference to the topology of the network, data flow, and router capacity. Remember that hello and routing updates are used differently than the point-to-point configuration. Therefore, you need to ensure that all the interfaces connecting into the cloud are configured in the same way; otherwise , the hellos will be rejected and no adjacency will be formed . The configuration for IS-IS over the fully meshed Frame Relay cloud is illustrated in Figure 12-4. In Figure 12-4, the Frame Relay cloud has three fully meshed routers, which can operate as a LAN as far as IS-IS PDUs are concerned. Figure 12-4. NBMA Frame Relay Cloud Running Broadcast Integrated IS-IS  Example 12-5 shows a working example of the configuration. In the example, the frame-relay map ip command maps the IP destination address to the outgoing data-link connection identifier (DLCI) and defines the interface as a broadcast interface. Integrated IS-IS uses the links as if they were truly a broadcast link and elects a DIS. The frame-relay map clns command maps to the CLNS process on the destination router. Without the this command, no routes appear in the IP routing table because IS-IS does not receive IS-IS frames to populate the IP routing table. Remember that these are IP routes carried in the IS-IS routing protocol. IS-IS information does not travel in IP or CLNS packets. IS-IS is encapsulated at the network layer in a frame that is similar to CLNS and those frames must be carried over Frame Relay to build the routing table. Example 12-5. NBMA Frame Relay Cloud Running Broadcast Integrated IS-IS Working Example for Router A ! interface Ethernet0 ip address 140.100.96.1 255.255.255.0 ip router isis isis circuit-type level-1 ! interface Serial0 ip address 140.100.64.1 255.255.255.0 ip router isis encapsulation frame-relay clockrate 56000 frame-relay map clns 629 broadcast !Map the layer 2 DLCI address in Frame Relay to the clns process of Router C frame-relay map clns 931 broadcast !Map the layer 2 DLCI address in Frame Relay to the clns process of Router B frame-relay map ip 140.100.64.2 931 broadcast ! Map the layer 2 DLCI address in Frame Relay to the Destination IP address of Router B frame-relay map ip 140.100.64.3 629 broadcast !Map the layer 2 DLCI address in Frame Relay to the Destination IP address of Router C isis circuit-type level-2-only ! interface Serial1 No ip address Shutdown ! ! router isis net 49.0001.0000.0000.000a.00 ! ip classless The alternative solution to a broadcast configuration is to define subinterfaces and to configure each subinterface as point-to-point. The Point-to-Point Configuration over NBMA The point-to-point configuration over NBMA requires an IP subnet per link. This is the configuration suggested by Cisco for a hub and spoke topology. The configuration is simpler, because the link is point-to-point and there is no need to configure frame-relay map commands. The point-to-point link is just a pipe that goes to one destination, and map commands imply a choice of destination. As shown in the configuration in Example 12-6, it is only necessary to create subinterfaces, configure those interfaces as point-to-point, start Frame Relay, and define the DLCIs. Do not forget that in addition to configuring Frame Relay, you must start the IS-IS process for each interface. Figure 12-5 supports the working example for this configuration. It shows the DLCI addresses and the IP addresses for the point-to-point links in addition to the ISO addresses for Routers A, B, and C. Figure 12-5. NBMA Frame Relay Cloud Running Point-to-Point Integrated IS-IS  Example 12-6 shows the configuration for Router A to run Integrated IS-IS across the Frame Relay cloud as if it were a series of point-to-point networks. Example 12-6. NBMA Frame Relay Cloud Running Point-to-Point Integrated IS-IS Working Example for Router A ! interface Ethernet0 ip address 140.100.96.1 255.255.255.0 ip router isis ! interface Serial0 no ip address encapsulation frame-relay !Configure Frame Relay for the interface no fair-queue clockrate 56000 ! interface Serial0.1 point-to-point !Configure the subinterface to be point-to-point ip address 140.100.64.1 255.255.255.0 ip router isis frame-relay interface-dlci 629 !Configure Frame Relay and define the DLCI to the destination interface Serial0.2 point-to-point ! Configure the subinterface to be point-to-point ip address 140.100.32.1 255.255.255.0 ip router isis frame-relay interface-dlci 931 ! Configure Frame Relay and define the DLCI to the destination ! router isis net 49.0001.0000.0000.000a.00 ! ip classless Verifying the Integrated IS-IS Operation The ability to monitor the network enables you to optimize the network and detect problems early. Useful commands to verify the operation of Integrated IS-IS include the following show commands: The following sections explain each of these show commands in more detail. The commands explained in this section correspond to the topology illustrated in Figure 12-6 and the configuration shown in Example 12-7 for Router A. Figure 12-6. The Network Topology for the show Commands  Example 12-7. The Configuration for Router A in Figure 12-6 Working Example for Router A interface Ethernet0 ip address 140.100.96.1 255.255.255.0 ip router isis isis circuit-type level-1 ! interface Serial0 no ip address encapsulation frame-relay no fair-queue clockrate 56000 ! interface Serial0.1 point-to-point ip address 140.100.64.1 255.255.255.0 ip router isis isis circuit-type level-2-only frame-relay interface-dlci 629 ! interface Serial0.2 point-to-point ip address 140.100.32.1 255.255.255.0 ip router isis isis circuit-type level-2-only frame-relay interface-dlci 931 ! ! router isis net 49.0001.0000.0000.000a.00 ! ip classless The show clns neighbors Command The show clns neighbors command has some of the contents of the neighbor table and the state of the link. Note that the subnetwork point of attachment (SNPA) is the MAC address of the interface. The type of routing that is used is Level 1-2. The EXEC command has the following syntax: show clns area-tag neighbors [ type number ] [ area ] [ detail ] Table 12-2 explains the syntax of this command. Table 12-2. Explanation of the show clns neighbors Command | Field | Description | | area-tag | Used primarily in multiarea Integrated IS-IS configurations. This is a name for an Integrated IS-IS routing process on a router. Each name must be unique to the process on the router. If an area tag is specified, output is limited to the specified area. | | type number | (Optional) Type of interface (for example, Ethernet). (Optional) Interface number (for example, Ethernet 1). | | area | (Optional) Shows the CLNS multiarea adjacencies. | | detail | (Optional) Shows details of each adjacency rather than a summary display. | Example 12-8 shows output for the show clns neighbors command. Example 12-8. Output for the show clns neighbors Command Working Example for Router A RouterA# show clns neighbors System Id Interface SNPA State Holdtime Type Protocol 0000.0000.000B Se0.2 DLCI 931 Up 22 L2 IS-IS 0000.0000.000C Se0.1 DLCI 629 Up 23 L2 IS-IS 0000.0000.000D Et0 00e0.1e3d.d56f Up 8 L1 IS-IS The output of the show clns neighbors command shows that Router A has three neighbors. The system ID shows that the serial subinterface S0.1 has heard an LSP from 0000.0000.000C S0.1, which has the data-link DLCI Frame Relay address of 629. The protocol is IS-IS, and it is running Level 2 routing. The link is up and has 23 seconds before another Hello needs to be received. Because the Hello timer is set by default to send Hellos every 10 seconds, it should receive another Hello in 7 seconds, which will reset the holdtime. The Ethernet segment is running Level 1 routing and has a MAC address for the SNPA address. The show clns neighbors command is good for quickly checking connectivity. This output shows all the neighborscomplete with the DLCI addresses and OSI system IDsindicating that Frame Relay is correctly configured and working, as is IS-IS. Adding the parameter detail to the show clns neighbors command gives information about each neighbor and the connection to that neighbor. Example 12-9 shows output for the show clns neighbors detail command. Here the area address for the neighbor, the IP address of the transmitting interface, and the length of time that the interface has been up are shown. This command gives information that enables you to verify the addressing scheme of the network. Example 12-9. Output for the show clns neighbors detail Command Working Example for Router A RouterA# show clns neighbor detail System Id Interface SNPA State Holdtime Type Protocol 0000.0000.000B Se0.2 DLCI 931 Up 27 L2 IS-IS Area Address(es): 49.0002 IP Address(es): 140.100.32.2* Uptime: 00:05:17 0000.0000.000C Se0.1 DLCI 629 Up 28 L2 IS-IS Area Address(es): 49.0003 IP Address(es): 140.100.64.3* Uptime: 00:05:22 0000.0000.000D Et0 00e0.1e3d.d56f Up 7 L1 IS-IS Area Address(es): 49.0001 IP Address(es): 140.100.96.2* Uptime: 00:15:01 Table 12-3 explains the meaning of the fields in the output. The command explained is with the detail parameter to cover all the fields shown in both output examples. Table 12-3. Explanation of the show clns neighbors detail Command Output | Field | Description | | System Id | The system address. It identifies a system in an area. Cisco defines this to be a 6-octet identifier. | | SNPA | Subnetwork point of attachment. This is the data-link address. | | Interface | Interface through which the neighbor was learned. | | State | State of the ES or IS. The states are as follows: -
Init The status of the adjacency is initializing. The router is waiting for an Integrated IS-IS Hello message. Until the Hello is received, the neighbor is not adjacent. -
Up Considers the other system reachable . -
Down Considers the other system unreachable. | | Holdtime | Number of seconds before this adjacency entry times out. | | Type | The types of adjacency are as follows: | | L1 | (Optional) Displays the router adjacencies for Level 1. | | L1L2 | (Optional) Displays the router adjacencies for Level 1 and 2. | | L2 | (Optional) Displays the router adjacencies for Level 2. | | Protocol | The routing protocol used to learn the adjacency. The protocol might be ES-IS, IS-IS, ISO IGRP, Static, or DECnet. | The show clns interface Command The misconfiguration of the interface for Integrated IS-IS results in the inability to create adjacencies. Typically, the error is a simple mismatch of parameters, which can be seen by using the show clns interface command. The neighbor database tells you of one neighbor, and the interface indicates one adjacency. Because this is a LAN interface, it is possible to identify the DIS. The circuit ID shows the pseudonode ID, which has a value greater than 0x00 in the octet after the system ID. Note that a DIS is elected for both Level 1 and Level 2 routing. Because no priority has been manually configured, the tiebreaker used to elect the DIS is the highest SNPA on the segment. In this case, the SNPA is the MAC address. Note that the default metric is 10 and the priority is 64. The EXEC command has the following syntax: Router# show clns interface [ type number ] In this example, Frame Relay is configured with point-to-point links. Because there is only one other router on this link, there is no need for a DIS to be elected. Therefore, the circuit ID shows the system ID of a router, rather than a pseudonode. Remember, the octet following the system ID indicates whether this ID is a pseudonode representing the multiaccess link. If the ID is that of a pseudonode, the system ID is that of the DIS, with the next octet showing a nonzero value such as 0x01. This makes more sense when you look at the Ethernet interface. The Ethernet 0 interface has the Level 1 circuit ID as A.01. This indicates that the DIS for Level 1 is Router A. The octet following the circuit ID of 01 has a nonzero value, indicating the ID of a pseudonode. Because this is a Level 1-2 router, there is also a circuit ID for the Level 2 adjacency. This is relevant only on the Ethernet interface because it is the only multiaccess link. Note that the value for the Level 2 DIS is that of Router A. Router D has been configured as a Level 1 router and, as such, cannot communicate Level 2 updates. Example 12-10 shows output for the show clns interface command. Example 12-10. Output for the show clns interface Command Working Example for Router A RouterA# show clns interface Ethernet0 is up, line protocol is up Checksums enabled, MTU 1497, Encapsulation SAP ERPDUs enabled, min. interval 10 msec. CLNS fast switching enabled 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 0x1 Level-1 Metric: 10, Priority: 64, Circuit ID: A.01 Number of active level-1 adjacencies: 0 Level-2 Metric: 10, Priority: 64 , Circuit ID A.01 Number of active level-2 adjacencies: 1 Next IS-IS LAN Level-1 Hello in 1 seconds Next IS-IS LAN Level-2 Hello in 1 seconds Serial0 is up, line protocol is up CLNS protocol processing disabled Serial0.1 is up, line protocol is up Checksums enabled, MTU 1500, Encapsulation FRAME-RELAY ERPDUs enabled, min. interval 10 msec. CLNS fast switching disabled CLNS SSE switching disabled DEC compatibility mode OFF for this interface Next ESH/ISH in 58 seconds Routing Protocol: IS-IS Circuit Type: level-1-2 Interface number 0x1, local circuit ID 0x100 Level-1 Metric: 10, Priority: 64 , Circuit ID: A.00 Number of active level-1 adjacencies: 0 Level-2 Metric: 10, Priority: 64 , Circuit ID: A.00 Number of active level-2 adjacencies: 1 Next IS-IS Hello in 2 seconds Serial0.2 is up, line protocol is up Checksums enabled, MTU 1500, Encapsulation FRAME-RELAY ERPDUs enabled, min. interval 10 msec. CLNS fast switching disabled CLNS SSE switching disabled DEC compatibility mode OFF for this interface Next ESH/ISH in 24 seconds Routing Protocol: IS-IS Circuit Type: level-1-2 Interface number 0x2, local circuit ID 0x101 Level-1 Metric: 10, Priority: 64 , Circuit ID: A.00 Number of active level-1 adjacencies: 0 Level-2 Metric: 10, Priority: 64 , Circuit ID: A.00 Number of active level-2 adjacencies: 1 Next IS-IS Hello in 886 milliseconds Table 12-4 explains the meaning of the fields in the output screen. Table 12-4. Explanation of the show clns interface Command Output | Field | Description | | Checksum | This may be either enabled or disabled. | | MTU | The number following MTU is the maximum transmission size for a packet on this interface. Note that the MTU is not 1500 because 3 bytes are taken by the OSI header. | | Encapsulation | The encapsulation is always SAP (ISO1). | | Routing Protocol | This indicates whether ES-IS or IS-IS is running. This determines the type of Hellos sent. | | Circuit Type | This indicates whether the link is enabled for L1, L2, or L1-2 routing. This determines the Hellos that are sent. | | Level-1 Metric | The metric value for the outbound interface for Level 1 routing. Note that the default setting is 10. | | Priority | The priority setting for DIS election. Note that the default of 64 is used. | | Circuit ID | This identifies the DIS for L1 if there is one on the link. | | Number of Active Level-1 Adjacencies | The number of L1 adjacencies formed on this link. | | Level-2 Metric | The metric value for the outbound interface for Level 2 routing. Note that the default setting is 10. | | Priority | The priority setting for DIS election. Note that the default of 64 is used. | | Circuit ID | This identifies the DIS for L2 if there is one on the link. | | Number of Active Level-2 Adjacencies | The number of L2 adjacencies formed on this link. | | Next IS-IS LAN Level-1 Hello | The number of seconds before the next Hello is expected. This is a good troubleshooting tool, because you can repeat the command to see whether the Hellos are received. | | Next IS-IS LAN Level-2 Hello | The number of seconds before the next Hello is expected. This is a good troubleshooting tool, because you can repeat the command to see whether the Hellos are received. | The show isis database Command The show isis database command shows the LSPs held in the local database. The LSP ID shows the system ID of the generating router and whether this LSP is from a router or a pseudonode. The last octet shows whether the LSP was too large to fit into one PDU; a nonzero value in this field indicates that this is a fragment of an LSP. The number states the fragment number. Because IS-IS is a link-state protocol, the database should be identical on every router of the same level within the area. The EXEC command has the following syntax: show isis area-tag database [ level-1 ] [ level-2 ] [ l1 ] [ l2 ] [ detail ] [ lspid ] Table 12-5 explains the syntax of this command. Table 12-5. Explanation of the show isis database Command | Field | Description | | area-tag | Used primarily in multiarea Integrated IS-IS configurations. This is a name for an Integrated IS-IS routing process on a router. Each name must be unique to the process on the router. If an area tag is specified, output is limited to the specified area. Required for multiarea Integrated IS-IS configuration. Optional for conventional Integrated IS-IS configuration. | | level-1 | (Optional) Displays the Integrated IS-IS link-state database for Level 1. | | level-2 | (Optional) Displays the Integrated IS-IS link-state database for Level 2. | | l1 | (Optional) Abbreviation for level-1 . | | l2 | (Optional) Abbreviation for level-2 . | | detail | (Optional) Shows the contents of each LSP rather than a summary display. | | lspid | (Optional) Identifier for the link-state PDU. Shows the contents of the specified individual LSP. | Example 12-11 shows output for the show isis database command. Example 12-11. Output for the show isis database Command RouterA# show isis database IS-IS Level-1 Link State Database: LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL A.00-00 * 0x00000017 0x76D5 876 1/0/0 IS-IS Level-2 Link State Database: LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL A.00-00 * 0x00000018 0xB74F 881 0/0/0 0000.0000.000B.00-00 0x0000001A 0xB561 872 0/0/0 0000.0000.000B.01-00 0x00000016 0x6045 1095 0/0/0 C.00-00 0x0000001E 0x6267 869 0/0/0 C.01-00 0x00000002 0xF25F 958 0/0/0 0000.0000.000E.00-00 0x00000018 0x010A 858 0/0/0 0000.0000.000D.00-00 0x0000001A 0x413C 985 0/0/0 0000.0000.000D.04-00 0x00000017 0xFCA0 1006 0/0/0 Table 12-6 explains the meaning of the fields in the output. Note that both Level 1 and Level 2 databases are shown because the router is running the default configuration of Level 1-2 routing. All the LSP information is contained in these databases, including the LSPs generated by the router itself. An asterisk marks these entries in the output. Table 12-6. Explanation of the show isis database Command | Field | Description | | LSPID | The LSPID indicates the transmitting router. The system ID is followed by two octets. If the first octet has a value greater than 0x00, this indicates that the ID is that of the pseudonode and the system ID is that of the DIS. The last octet is the Fragment bit. If the value is 0x00, the entire LSP was carried in one LSP. If the value is greater than 0x00, it indicates that this PDU is the n th fragment of the LSP. | | LSP Seq Num | Sequence number for the LSP. This allows routers to determine whether they have received the latest information from the source and ensures the integrity of the link-state database. | | LSP Checksum | Checksum of the entire LSP packet. | | LSP Holdtime | Amount of time the LSP remains valid (in seconds). An LSP holdtime of 0 indicates that this LSP was purged and is being removed from the link-state database. | | ATT | The LSP indicates that this router is a Level 2 router with a path out of the area. Level 1 routers use the presence of this bit to identify the closest Level 1-2 router to send their out-of-area data. | | P | Partition repair capability. Not supported by Cisco. | | OL | The Overload bit indicates that the router has an incomplete database because of memory overload and is therefore not used for transit data. | The show isis database detail Command The show isis database detail command shows the complete LSP and the values for the individual fields. The EXEC command has the same syntax structure as shown in the show isis database command in the preceding section. Example 12-12 shows output for the show isis database detail command. The highlighted lines show that there are two databases: one for the Level 1 routing and the other for the Level 2 routing. The example shows, for each LSP, the area and the IP address of the transmitting interface and the metric cost to the IP routes it knows . The default metric is a cost of 10; therefore, a metric of 20 indicates a route that is two hops away. Example 12-12. Output for the show isis database detail Command RouterA# show isis database detail IS-IS Level-1 Link State Database: LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL A.00-00 * 0x00000017 0x76D5 873 1/0/0 Area Address: 49.0001 NLPID: 0xCC Hostname:A IP Address: 140.100.32.1 Metric: 10 IP 140.100.96.0 255.255.255.0 Metric: 10 IP 140.100.64.0 255.255.255.0 Metric: 10 IP 140.100.32.0 255.255.255.0 Metric: 10 IS A.01 IS-IS Level-2 Link State Database: LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL A.00-00 * 0x00000018 0xB74F 877 0/0/0 Area Address: 49.0001 NLPID: 0xCC Hostname: A IP Address: 140.100.32.1 Metric: 10 IS 0000.0000.000B.00 Metric: 10 IS C.00 Metric: 10 IS 0000.0000.000D.04 Metric: 10 IP 140.100.96.0 255.255.255.0 Metric: 10 IP 140.100.64.0 255.255.255.0 Metric: 10 IP 140.100.32.0 255.255.255.0 0000.0000.000B.00-00 0x0000001A 0xB561 868 0/0/0 Area Address: 49.0002 NLPID: 0xCC IP Address: 140.100.16.2 Metric: 10 IS 0000.0000.000B.01 Metric: 10 IS A.00 Metric: 10 IS C.00 Metric: 10 IP 140.100.104.0 255.255.255.0 Metric: 20 IP 140.100.105.0 255.255.255.0 Metric: 20 IP 140.100.106.0 255.255.255.0 Metric: 20 IP 140.100.107.0 255.255.255.0 Metric: 10 IP 140.100.32.0 255.255.255.0 Metric: 10 IP 140.100.16.0 255.255.255.0 0000.0000.000B.01-00 0x00000016 0x6045 1089 0/0/0 Metric: 0 IS 0000.0000.000B.00 Metric: 0 IS 0000.0000.000E.00 C.00-00 0x0000001E 0x6267 863 0/0/0 Area Address: 49.0003 NLPID: 0xCC Hostname: C IP Address: 140.100.100.1 Metric: 10 IS C.02 Metric: 10 IS A.00 Metric: 10 IS 0000.0000.000B.00 Metric: 10 IP 140.100.100.0 255.255.255.0 Metric: 10 IP 140.100.64.0 255.255.255.0 Metric: 10 IP 140.100.16.0 255.255.255.0 C.01-00 0x00000002 0xF25F 951 0/0/0 Metric: 0 IS C.00 0x00000018 0x010A 850 0/0/0 Area Address: 49.0002 0000.0000.000E.00-00 NLPID: 0xCC IP Address: 140.100.105.1 Metric: 10 IS 0000.0000.000B.01 Metric: 10 IP 140.100.104.0 255.255.255.0 Metric: 10 IP 140.100.105.0 255.255.255.0 Metric: 10 IP 140.100.106.0 255.255.255.0 Metric: 10 IP 140.100.107.0 255.255.255.0 Metric: 20 IP 140.100.32.0 255.255.255.0 Metric: 20 IP 140.100.16.0 255.255.255.0 0000.0000.000D.00-00 0x0000001A 0x413C 976 0/0/0 Area Address: 49.0003 NLPID: 0xCC IP Address: 140.100.97.1 Metric: 10 IS 0000.0000.000D.04 Metric: 10 IP 140.100.96.0 255.255.255.0 Metric: 10 IP 140.100.97.0 255.255.255.0 Metric: 10 IP 140.100.98.0 255.255.255.0 Metric: 10 IP 140.100.99.0 255.255.255.0 0000.0000.000D.04-00 0x00000017 0xFCA0 996 0/0/0 Metric: 0 IS 0000.0000.000D.00 Metric: 0 IS A.00 Table 12-7 explains the meaning of the fields in the output. Table 12-7. Explanation of the show isis database detail Command | Field | Description | | Area Address | Area addresses that may be reached from this router. L1 LSPs describe the area addresses configured manually on the originating router. L2 LSPs describe the area addresses for the area to which this route belongs. | | Metric | The cost of the outbound interface between the originating router and the advertised neighbor, or the metric of the compound cost between the advertising router and the advertised destination. | Troubleshooting the Integrated IS-IS Operation Unfortunately, even after the most careful planning, configurations can fail to work, and the most scrutinized networks can break. The show commands are essential for hunting down problems. Careful documentation of the troubleshooting steps taken enable the administrator to build a solid understanding of the problem and systematically eliminate possible problem sources. Having this log is invaluable when, if all else fails, you have to elicit the help of the Technical Assistance Center (TAC) engineers at Cisco. The following commands are useful for troubleshooting Integrated IS-IS: -
show isis spf-log -
debug commands The following sections describe these commands in greater detail. The show isis spf-log Command The show isis spf-log command explains a great deal about the SPF calculations on the router. It gives the events that triggered SPF for the last 20 occurrences. To display how often and why the router has run a full SPF calculation, use the show isis spf-log EXEC command. Example 12-13 shows output for the show isis spf-log command. The highlighted lines show the normal periodic SPF calculations. The example also shows that Router A sent an LSP because it had set the ATT bit, and later it generated a new LSP when new adjacencies came online. This output shows the healthy workings of an IS-IS network, but the command is very useful if the network appears unstable, with routes appearing and disappearing . Example 12-13. Output for the show isis spf-log Command RouterA# show isis spf-log Level 1 SPF log When Duration Nodes Count Last trigger LSP Triggers 04:23:24 0 1 1 A.00-00 TLVCODE 04:08:46 0 1 1 PERIODIC 03:53:46 0 1 1 PERIODIC 03:38:46 0 1 1 PERIODIC 03:23:46 0 1 1 PERIODIC 03:08:46 0 1 1 PERIODIC 02:53:46 0 1 1 PERIODIC 02:38:46 0 1 1 PERIODIC 02:23:46 0 1 1 PERIODIC 02:08:46 0 1 1 PERIODIC 01:53:46 0 1 1 PERIODIC 01:38:46 0 1 1 PERIODIC 01:23:46 0 1 1 PERIODIC 01:08:46 0 1 1 PERIODIC 00:53:46 0 1 1 PERIODIC 00:38:47 0 1 1 PERIODIC 00:23:47 0 1 1 PERIODIC 00:15:14 0 1 2 A.00-00 ATTACHFLAG LSPHEADER 00:08:46 0 1 1 PERIODIC Level 2 SPF log When Duration Nodes Count First trigger LSP Triggers 03:53:48 0 1 1 PERIODIC 03:38:48 0 1 1 PERIODIC 03:23:48 0 1 1 PERIODIC 03:08:48 0 1 1 PERIODIC 02:53:48 0 1 1 PERIODIC 02:38:48 0 1 1 PERIODIC 02:23:48 0 1 1 PERIODIC 02:08:48 0 1 1 PERIODIC 01:53:48 0 1 1 PERIODIC 01:38:48 0 1 1 PERIODIC 01:23:48 0 1 1 PERIODIC 01:08:48 0 1 1 PERIODIC 00:53:48 0 1 1 PERIODIC 00:38:48 0 1 1 PERIODIC 00:23:48 0 1 1 PERIODIC 00:15:22 0 3 5 A.00-00 NEWADJ LSPHEADER TLVCONTENT 00:08:48 0 3 1 PERIODIC 00:05:44 4 4 4 A.00-00 NEWADJ TLVCONTENT 00:05:38 4 7 5 0000.0000.000B.00-00 LSPHEADER TLVCONTENT Table 12-8 explains the meaning of the fields in the output screen. Table 12-8. Explanation of the show isis spf-log Command | Field | Description | | When | The amount of time since a full SPF calculation occurred (hh:mm:ss). The last 19 occurrences are shown. | | Duration | Number of milliseconds it took to complete this SPF run. This is elapsed time as opposed to CPU time. | | Nodes | Number of routers and pseudonodes (LANs) calculated in the SPF run. | | Count | This count shows the number of events (such as receiving new LSPs) that occurred while the router was waiting before running full SPF. The router waits five seconds after the first triggered LSP to ensure that all the information is received. | | Last Trigger LSP | Whenever a full SPF calculation is triggered by the arrival of a new LSP, the ID of the LSP is stored. The LSPID can indicate where to start troubleshooting for any routing instability in an area. If multiple LSPs are causing an SPF run, only the LSPID of the last received LSP is remembered . | | Trigger | A list of all events that triggered a full SPF calculation. | The debug Commands The debug command is a helpful troubleshooting tool, but it does have certain disadvantages of which you must be aware. The debug command has the highest process priority and forces the router into process switching. It is capable of consuming all the resources on the router, thus becoming the problem instead of helping to solve the problem. It is important to turn on debug just for the specific task to be monitored and to turn it off as soon as the data has been gathered. The no form of this command disables debugging output. You should direct the output to a log file, because each character sent to the console forces processor interrupt; in this way, the data can be perused with care. The debug commands are EXEC commands. Table 12-9 lists the options available for monitoring Integrated IS-IS. Table 12-9. The debug Command Options for Integrated IS-IS | Command Option | Description | | debug isis adjacencies-packets | Displays information on all adjacency- related activity. This includes the following: | | debug isis spf-statistics | Displays statistical information about building routes between routers. Using the statistical information provided, one can determine how long it takes to place a Level 1 IS or Level 2 IS on the shortest path tree (SPT) using the IS-IS protocol. | | debug isis update-packets | Displays SNPs (CSNPs and PSNPs) and LSPs that are detected by the router. | | 