Configuring IS-IS for IP Routing
| ‚ < ‚ Free Open Study ‚ > ‚ |
| This section reviews the basic tasks involved in enabling IS-IS on Cisco routers. In addition to the basic configuration, numerous Cisco IOS Software commands exist for enabling various optimization and management capabilities, such as modifying hello timers, logging IS-IS adjacency changes, performing authentication, and so on. Chapter 11 covers some of these options in greater detail. For completeness, however, you should consult the "IOS Network Protocols Configuration Guide," available at www.cisco.com. 8 Enabling IS-IS on point-to-point and LAN broadcast ‚ type links is simple and similar in both cases. Additionally, on LAN type links, you can use the interface-level command isis priority value to select a preferred router to be DIS. The default interface priority is 64. A higher value is preferred. The following sections provide examples that elaborate on configuring IS-IS specifically :
Configuring IS-IS on Point-to-Point Serial LinksFigure 10-14 shows two routers, RT1 and RT2, connected back to back by a serial link. Both routers are placed in the same IS-IS area. Figure 10-15 shows a similar setup but with RT1 and RT2 in different areas. The AreaIDs of RT1 and RT2 are mismatched to put them in different areas. Figure 10-14. IS-IS Configuration: Network Diagram for Example 10-2 Figure 10-15. IS-IS Configuration: Network Diagram for Example 10-3 The following two steps are required to enable basic IS-IS routing on Cisco routers:
The configuration command, router isis [ tag ], enables the IS-IS routing process. The tag is an optional keyword for labeling the routing process, and it is of significance only in the local router where it is used. Some service providers maintain the same tag on all routers in the domain, even though it is not required. It should be noted, however, that some old Cisco IOS Software releases require the tags to match between neighbor routers. By default, Cisco routers behave as Level 1 ‚ 2 when IS-IS first is enabled on them. The com-mand clns routing also is entered automatically into the configuration when the routing process is activated. An NSAP address must be configured on the router even if it is to be used to route only IP. The router-level command net { nsap } is used for this. A NET is an NSAP with a 0-value NSEL. The next step after configuring the routing process is to enable IS-IS routing on the interfaces where IS-IS routing is desired. The command ip router isis [ tag ] is sufficient for IP-only routing. The tag must be the same as the one used for the routing process. If ISO CLNP routing and packet forwarding are required, they can be enabled with the interface command clns router isis [ tag ]. Exclusive Level 1 or Level 2 routing can be enabled for individual interfaces with the interface-level command isis circuit type { level-1 level-2 level-1-2 }. The level-1-2 option restores the default behavior. The router-level command is-type { level-1 level-2-only level-1-2 } applies the preferred mode of operation to all interfaces simultaneously . In Figure 10-14, both routers are in the same area and share a common area prefix (49.0001). Therefore, according to the default Cisco IOS Software behavior, they establish Level 1 and Level 2 adjacencies. Example 10-2 shows the configuration for RT1 and RT2, which are depicted in Figure 10-14. Example 10-2 Configuring Point-to-Point IS-IS Neighbors in Same Areahostname RT1 clns routing ! interface Loopback0 ip address 10.1.1.1 255.255.255.255 ip router isis ! interface Serial0/0 ip address 192.168.1.1 255.255.255.252 ip router isis ! router isis net 49.0001.0000.0000.0001.00 _____________________________________________________________________________________ hostname RT2 clns routing ! interface Loopback0 ip address 10.1.1.2 255.255.255.255 ip router isis ! interface Serial0/0 ip address 192.168.1.2 255.255.255.252 ip router isis ! router isis net 49.0001.0000.0000.0002.00 In contrast to Figure 10-14, the routers in Figure 10-15 are in different areas, so they will form only a Level 2 adjacency. Example 10-3 shows the configuration for RT1 and RT2 depicted in Figure 10-15. Example 10-3 Configuring Point-to-Point IS-IS Neighbors in Different Areashostname RT1 ! interface Loopback0 ip address 10.1.1.1 255.255.255.255 ip router isis ! interface Serial2/0 ip address 192.168.1.1 255.255.255.252 ip router isis ! router isis net 49.0001.0000.0000.0001.00 _____________________________________________________________________________________ hostname RT2 ! interface Loopback0 ip address 10.1.1.2 255.255.255.255 ip router isis ! interface Serial2/0 ip address 192.168.1.2 255.255.255.252 ip router isis ! router isis net 49.0002.0000.0000.0002.00 The following commands are useful for verifying proper configuration and operation of IS-IS on Cisco routers:
The sections that follow provide example outputs from these show commands based on the router setup in Figure 10-15. Each example features output from each router (RT1 and RT2) to show the state of either side of the connection. Because the setup is basic, most of the output is self-explanatory. The "Integrated IS-IS Configuration Guide," at Cisco.com, 9 provides a detailed explanation of the fields in the show command output presented in these sections. show clns protocol CommandThe show clns protocol command lists the protocol-specific information for each IS-IS or ISO IGRP routing process in a router. Example 10-4 displays the show clns protocol command output for both routers depicted in Figure 10-15. Example 10-4 show clns protocol Command OutputRT1# show clns protocol IS-IS Router: <Null Tag> System Id: 0000.0000.0001.00 IS-Type: level-1-2 Manual area address(es): 49.0001 Routing for area address(es): 49.0001 Interfaces supported by IS-IS: Loopback0 - IP Serial0/0 - IP Redistributing: static Distance: 110 RRR level: none Generate narrow metrics: level-1-2 Accept narrow metrics: level-1-2 Generate wide metrics: none Accept wide metrics: none _____________________________________________________________________________________ RT2# show clns protocol IS-IS Router: <Null Tag> System Id: 0000.0000.0002.00 IS-Type: level-1-2 Manual area address(es): 49.0002 Routing for area address(es): 49.0002 Interfaces supported by IS-IS: Loopback0 - IP Serial0/0 - IP Redistributing: static Distance: 110 RRR level: none Generate narrow metrics: level-1-2 Accept narrow metrics: level-1-2 Generate wide metrics: none Accept wide metrics: none show clns neighbors detail CommandThe show clns neighbors detail command displays both end-system (ES) and intermediate-system (IS) neighbors. Example 10-5 displays the show clns neighbors detail command output for both routers depicted in Figure 10-15. Example 10-5 show clns neighbors detail Command OutputRT1# show clns neighbors detail System Id Interface SNPA State Holdtime Type Protocol RT2 Se0/0 *HDLC* Up 27 L2 IS-IS Area Address(es): 49.0002 IP Address(es): 192.168.1.2* Uptime: 00:48:46 _____________________________________________________________________________________ RT2# show clns neighbors detail System Id Interface SNPA State Holdtime Type Protocol RT1 Se0/0 *HDLC* Up 26 L2 IS-IS Area Address(es): 49.0001 IP Address(es): 192.168.1.1* Uptime: 00:52:14 show clns interface CommandThe show clns interface command lists the CLNS-specific or ES-IS information about each interface. Example 10-6 displays the show clns interface command output for both routers depicted in Figure 10-15. Example 10-6 show clns interface Command OutputRT1# show clns interface ser 0/0 Serial0/0 is up, line protocol is up Checksums enabled, MTU 1500, Encapsulation HDLC 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 enabled CLNS SSE switching disabled DEC compatibility mode OFF for this interface Next ESH/ISH in 3 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: RT1.00 Number of active level-1 adjacencies: 0 Level-2 Metric: 10, Priority: 64, Circuit ID: RT1.00 Number of active level-2 adjacencies: 1 Next IS-IS Hello in 8 seconds _____________________________________________________________________________________ RT2# show clns interface serial0/0 Serial0/0 is up, line protocol is up Checksums enabled, MTU 1500, Encapsulation HDLC 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 enabled CLNS SSE switching disabled DEC compatibility mode OFF for this interface Next ESH/ISH in 8 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: RT2.00 Number of active level-1 adjacencies: 0 Level-2 Metric: 10, Priority: 64, Circuit ID: RT2.00 Number of active level-2 adjacencies: 1 Next IS-IS Hello in 2 seconds show isis topology CommandThe show isis topology command displays a list of all connected routers in all areas. Example 10-7 displays the show isis topology command output for both routers depicted in Figure 10-15. Example 10-7 show isis topology Command OutputRT1# show isis top IS-IS paths to level-1 routers System Id Metric Next-Hop Interface SNPA RT1 -- IS-IS paths to level-2 routers System Id Metric Next-Hop Interface SNPA RT1 -- RT2 10 RT2 Se0/0 *HDLC* _____________________________________________________________________________________ RT2# show isis topology IS-IS paths to level-1 routers System Id Metric Next-Hop Interface SNPA RT2 -- IS-IS paths to level-2 routers System Id Metric Next-Hop Interface SNPA RT1 10 RT1 Se0/0 *HDLC* RT2 -- show isis database CommandThe show isis database command displays the IS-IS link-state database. Example 10-8 displays the show isis database command output for both routers depicted in Figure 10-15. Example 10-8 show isis database Command OutputRT1# show isis database IS-IS Level-1 Link State Database LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL RT1.00-00 * 0x00000008 0x8B75 1126 1/0/0 RT1.01-00 * 0x00000001 0x459B 1131 0/0/0 IS-IS Level-2 Link State Database LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL RT1.00-00 * 0x0000008A 0x8FED 1126 0/0/0 RT2.00-00 0x0000001E 0xB82C 998 0/0/0 _____________________________________________________________________________________ RT2# show isis database IS-IS Level-1 Link State Database LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL RT2.00-00 * 0x00000019 0x3DAB 883 1/0/0 RT2.01-00 * 0x0000000D 0x339F 980 0/0/0 IS-IS Level-2 Link State Database LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL RT1.00-00 0x0000008A 0x8FED 931 0/0/0 RT2.00-00 * 0x0000001E 0xB82C 808 0/0/0 Table 10-7 lists and explains the key fields in this command's output. Table 10-7. Explanation of show isis database Command Output
ATM Configuration ExamplesAs an NBMA medium, ATM connectivity can be configured as multipoint on a router's main interface or subinterfaces. Another configuration option is to use point-to-point connectivity on subinterfaces. Enabling IS-IS on ATM interfaces follows the same two steps for configuring IS-IS on point-to-point serial links:
The multipoint configuration works in the same way as the simple broadcast LAN described previously. Similarly, operation of the point-to-point configuration is just like the serial point-to-point setup. The IS-IS configuration for Frame Relay is analogous to the ATM setup options shown in this section. The large numbers of virtual circuits in NMBA clouds result in highly meshed point-to-point connections. Large meshes pose resource- related (memory and CPU) challenges to connected routers because of the high numbers of LSP required to be flooded and processed between the large number of connected neighbors (in the order of N 3 , where N is the number of nodes). It is strongly recommended that you use the IS-IS mesh group feature in highly meshed environ-ments to cut down on redundant flooding. Figure 10-16 shows a network diagram illustrating a simple ATM configuration using point-to-point subinterfaces. Figure 10-16. ATM Network: Point-to-Point Setup Example 10-9 shows the configuration for RT5 and RT6 depicted in Figure 10-16. Example 10-9 ATM Point-to-Point Configurationshostname RT5 ! clns routing ! interface ATM6/0.2 point-to-point ip address 10.1.1.5 255.255.255.252 no ip directed-broadcast ip router isis atm pvc 2 0 10 aal5snap ! router isis net 49.0001.0000.0000.0005.00 is-type level-2-only _____________________________________________________________________________________ hostname RT6 ! clns routing ! interface ATM6/0.2 point-to-point ip address 10.1.1.6 255.255.255.252 no ip directed-broadcast ip router isis atm pvc 2 0 10 aal5snap ! router isis net 49.0001.0000.0000.0006.00 is-type level-2-only int atm 6/0.2 point ip address . . . ip router isis pvc 0/10 encapsulation aal5snap Figure 10-17 shows the network diagram for the ATM multipoint configurations presented in Example 10-10. Figure 10-17. ATM Network: Multipoint Setup For multipoint configurations, the corresponding clns map statement is required, as shown in Example 10-10. In ATM, the clns map statements are placed under the ATM map list. Example 10-10 ATM Point-to-Point Configurationshostname RT7 ! clns routing ! interface ATM6/0.1 multipoint ip address 10.1.1.7 255.255.255.0 no ip directed-broadcast ip router isis atm pvc 1 0 8 aal5snap map-group ISIS_CONFIG ! router isis net 49.0001.0000.0000.0007.00 is-type level-2-only ! map-list ISIS_CONFIG ip 10.1.1.8 atm-vc 1 broadcast clns 49.0001.0000.0000.0008.00 atm-vc 1 broadcast _____________________________________________________________________________________ hostname RT8 ! clns routing ! interface ATM6/0.1 multipoint ip address 10.1.1.8 255.255.255.0 no ip directed-broadcast ip router isis atm pvc 1 0 8 aal5snap map-group ISIS_CONFIG ! router isis net 49.0001.0000.0000.0008.00 is-type level-2-only ! map-list ISIS_CONFIG ip 10.1.1.7 atm-vc 1 broadcast clns 49.0001.0000.0000.0007.00 atm-vc 1 broadcast Int atm 6/0 Pvc 0/5 Encapsulation qsaal IP Default Route AdvertisementIn IS-IS, Level 1 routers automatically install an IP default route to the nearest Level 1 ‚ 2 routers in the area. The Level 1 routers detect the Level 2 routers by the attached (ATT) bit setting in the Level 1 LSPs issued by Level 1 ‚ 2 routers. Level 1 ‚ 2 routers generate Level 1 LSPs into their local area and set the ATT bit in these LSPs to flag their connectivity to the backbone. On the other hand, a manual configuration is required to generate a default route into the Level 2 backbone. The router-level command default-information originate allows a Level 2 router to advertise a default route into the backbone, which will be seen by other Level 2 routers. The command causes a default route to be inserted into the Level 2 LSP of the advertising router. Unlike similar configurations in other IP routing protocols, an explicit static default route is not required to back up the default-information originate command. Figure 10-18 shows the network diagram for illustrating usage of the default information provided in Example 10-11. Figure 10-18. Network Diagram for Example 10-11 Example 10-11 shows excerpts of the configuration file of a router with the default-information originate command enabled under the IS-IS routing process. Also shown is the Level 2 LSP featuring a default route entry with a metric of 0. Example 10-11 Using the default-information originate CommandRT1# show running-config [snip] Hostname RT1 ! router isis default-information originate net 49.0001.0000.0000.0001.00 [snip] _____________________________________________________________________________________ RT2# show isis database detail RT1.00-00 level-2 IS-IS Level-2 LSP RT1.00-00 LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL RT1.00-00 0x000000E1 0x7A1E 651 0/0/0 Area Address: 49.0001 NLPID: 0xCC Hostname: RT1 IP Address: 10.1.1.1 Metric: 10 IS RT1.01 Metric: 10 IS RT2.00 Metric: 0 IP 0.0.0.0 0.0.0.0 Metric: 10 IP 10.1.1.1 255.255.255.255 Metric: 10 IP 192.168.1.0 255.255.255.252 Route RedistributionThe IS-IS protocol considers all routes learned by a router from other sources, such as static routes, the Routing Information Protocol (RIP), and Open Shortest Path First (OSPF), as external routes. External routes can be introduced into the IS-IS environment by means of route redistribution. The procedure can also be used to advertise IS-IS routes into another routing protocol, such as OSPF. This section focuses on the former, redistributing routes into IS-IS. RFC 1195 allows redistribution into only the Level 2 routing environment. For practical pur-poses, however, Cisco IOS Software allows redistribution into Level 1 as well. This cap-ability primarily was required by service providers who built single Level 1 IS-IS areas for their IGP infrastructures , to avoid suboptimal routing issues in hierarchical architectures in the absence of domain-wide prefix distribution. Having external IP reachability information in Level 1 LSPs should not pose any interoperability problems because IS-IS routers are not expected to parse any unknown TLVs in an IS-IS packet. They should just skip them to the next supported TLV. The configuration and mechanisms underlying operation of route redistribution are elaborated in Example 10-12, which is based on Figure 10-19. Figure 10-19. Network Diagram: Redistribution Example As in the case of other IP routing protocols, redistribution of IP static routes into IS-IS requires explicit configuration with the router-level command redistribute. The complete command for IS-IS is redistribute source ip options. Note that the ip keyword is required on the command line to specify that the operation is relevant to IP routing. You might recall that Integrated IS-IS supports both IP and CLNP routing. Other configuration options of the redistribute command include a metric value, a metric type, a route map, and so on. The route map option provides a mechanism for filtering routes im-ported into the IS-IS environment. By default, the metric type internal is assigned to external routes, and they are added into only the Level 2 environment if no level is specified. This is demonstrated in Example 10-12. The highlighted line in the show running-config output shows the redistribution command line in the configuration file. The highlighted line in the show isis database output shows an external route in an LSP. The last output in Example 10-12 shows a show ip route command output from Router RT2; the highlighted line is the external route that was originated from RT1. Example 10-12 Configuring Basic Route RedistributionRT1#show running-config [snip] router isis redistribute static ip metric 0 metric-type internal level-2 default-information originate net 49.0001.0000.0000.0001.00 _____________________________________________________________________________________ RT2# show isis database level-2 detail RT1.00-00 IS-IS Level-2 LSP RT1.00-00 LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL RT1.00-00 0x000000F3 0x04DF 956 0/0/0 Area Address: 49.0001 NLPID: 0xCC Hostname: RT1 IP Address: 10.1.1.1 Metric: 10 IS RT1.01 Metric: 10 IS RT2.00 Metric: 0 IP 0.0.0.0 0.0.0.0 Metric: 0 IP-External 10.4.4.0 255.255.255.0 Metric: 10 IP 10.1.1.1 255.255.255.255 Metric: 10 IP 192.168.1.0 255.255.255.252 RT2# show ip route [snip] Gateway of last resort is 192.168.1.1 to network 0.0.0.0 10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks C 10.1.1.2/32 is directly connected, Loopback0 i L2 10.4.4.0/24 [115/10] via 192.168.1.1, Serial0/0 i L2 10.1.1.1/32 [115/20] via 192.168.1.1, Serial0/0 192.168.1.0/30 is subnetted, 1 subnets C 192.168.1.0 is directly connected, Serial0/0 i*L2 0.0.0.0/0 [115/10] via 192.168.1.1, Serial0/0 In Example 10-13, the metric type explicitly is configured and specified to be external. Internal metrics are comparable to metrics used for internal routes; external metrics require the I/E bit of the metric field to be set, bumping up the value of the metric applied. CAUTION Cisco IOS Software sets bit 8 instead of bit 7 for the I/E bit when using narrow metrics, which results in an increase in the metric value by 128 instead of 64. Example 10-13 Specifying External Metric Type in IS-IS RedistributionRT1# show running-config [snip] router isis redistribute static ip metric 0 metric-type external level-2 default-information originate net 49.0001.0000.0000.0001.00 ! ip route 10.4.4.0 255.255.255.0 Null0 _____________________________________________________________________________________ RT2# show isis data level-2 detail RT1.00-00 IS-IS Level-2 LSP RT1.00-00 LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL RT1.00-00 0x000000F1 0xA7BD 727 0/0/0 Area Address: 49.0001 NLPID: 0xCC Hostname: RT1 IP Address: 10.1.1.1 Metric: 10 IS RT1.01 Metric: 10 IS RT2.00 Metric: 0 IP 0.0.0.0 0.0.0.0 Metric: 128 IP-External 10.4.4.0 255.255.255.0 Metric: 10 IP 10.1.1.1 255.255.255.255 Metric: 10 IP 192.168.1.0 255.255.255.252 RT2# show ip route [snip] Gateway of last resort is 192.168.1.1 to network 0.0.0.0 10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks C 10.1.1.2/32 is directly connected, Loopback0 i L2 10.4.4.0/24 [115/138] via 192.168.1.1, Serial0/0 i L2 10.1.1.1/32 [115/20] via 192.168.1.1, Serial0/0 192.168.1.0/30 is subnetted, 1 subnets C 192.168.1.0 is directly connected, Serial0/0 i*L2 0.0.0.0/0 [115/10] via 192.168.1.1, Serial0/0 The highlighted line in Example 10-13 shows the redistribute command syntax with the metric type specified as external. The corresponding external entry is highlighted in the show isis database output with a metric of 128 instead of the 0 that was featured in Example 10-12. The external route advertised from RT1 is highlighted in the show ip route output of RT2 at the end of the example. IP Route SummarizationAn IS-IS router can be configured to summarize IP routes into Level 1, Level 2, or both with the following router-level configuration command: summary-address prefix [ level-1 level-2 level-1-2 ]. By default, summaries go into Level 2 if no level is specified on the command line. Example 10-14 displays a sample configuration and related show command outputs based on Figure 10-20. In the example provided, the IP subnet assigned to Ethernet0/0 of RT1, 11.1.1.0/24, is summarized as 11.0.0.0/8. The summary route 11.0.0.0/8 then is observed at RT2. Figure 10-20. Network Diagram: IP Route Summarization Example The highlighted line in the show running-config output provided in Example 10-14 shows the command line on RT1. The highlighted line in the show isis database output shows the summary entry in RT1's LSP, and the highlighted line in the show ip route on RT2 shows evidence that the summary route has been propagated to other Level 2 routers. Example 10-14 Route Summarization Configuration ExampleRT1# show running-config interface Ethernet0/0 ip address 11.1.1.1 255.255.255.0 ip router isis ! interface Serial0/0 ip address 192.168.1.1 255.255.255.252 ip router isis ! router isis summary-address 11.0.0.0 255.0.0.0 redistribute static ip metric 0 metric-type internal level-2 default-information originate net 49.0001.0000.0000.0001.00 _____________________________________________________________________________________ RT2# show isis data level-2 detail RT1.00-00 IS-IS Level-2 LSP RT1.00-00 LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL RT1.00-00 0x000000F7 0xF8AA 518 0/0/0 Area Address: 49.0001 NLPID: 0xCC Hostname: RT1 IP Address: 10.1.1.1 Metric: 10 IS RT1.02 Metric: 10 IS RT1.01 Metric: 10 IS RT2.00 Metric: 0 IP 0.0.0.0 0.0.0.0 Metric: 0 IP-External 10.4.4.0 255.255.255.0 Metric: 10 IP 10.1.1.1 255.255.255.255 Metric: 10 IP 192.168.1.0 255.255.255.252 Metric: 10 IP 11.0.0.0 255.0.0.0 RT2# show ip route [snip] Gateway of last resort is 192.168.1.1 to network 0.0.0.0 10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks C 10.1.1.2/32 is directly connected, Loopback0 i L2 10.4.4.0/24 [115/10] via 192.168.1.1, Serial0/0 i L2 10.1.1.1/32 [115/20] via 192.168.1.1, Serial0/0 i L2 11.0.0.0/8 [115/20] via 192.168.1.1, Serial0/0 192.168.1.0/30 is subnetted, 1 subnets C 192.168.1.0 is directly connected, Serial0/0 i*L2 0.0.0.0/0 [115/10] via 192.168.1.1, Serial0/0 |
| ‚ < ‚ Free Open Study ‚ > ‚ |
EAN: 2147483647
Pages: 260