Purpose
Assuming that all the routers are correctly configured for IS-IS, you can verify which neighbors are adjacent and able to exchange IS-IS data. In addition, you can examine the set of routes installed in the forwarding table to verify that the routing protocol process (rpd) has relayed the correct information into the forwarding table.
Figure 9 illustrates the example IS-IS topology used for the procedures in this topic.
Figure 9: IS-IS Network Topology
The network consists of Level 1 and Level 2 adjacencies. Level 1 adjacencies are within areas 49.0001 and 49.0002. Level 2 adjacencies occur between all directly connected Level 2 routers regardless of which area they are in. For example, R5 is in area 49.0001, R6 is in area 49.0003, R1 is in area 49.0004, and R2 is in area 49.0002. The network in Figure 9 should have the following adjacencies:
To verify that routers are adjacent and able to exchange IS-IS data, follow these steps:
To verify that routers are adjacent and able to exchange IS-IS data.
To verify that routers are adjacent and able to exchange IS-IS data, enter the following CLI operational mode command:
The following sample output shows the adjacencies that formed for all routers shown in Figure 9:
user@R1> show isis adjacency Interface System L State Hold (secs) SNPA so-0/0/0.0 R2 2 Up 19 so-0/0/1.0 R5 2 Up 18 user@R2> show isis adjacency Interface System L State Hold (secs) SNPA so-0/0/0.0 R1 2 Up 19 so-0/0/1.0 R3 1 Up 26 so-0/0/2.0 R6 2 Up 21 user@R3> show isis adjacency Interface System L State Hold (secs) SNPA so-0/0/1.0 R2 1 Up 24 user@R4> show isis adjacency Interface System L State Hold (secs) SNPA so-0/0/2.0 R5 1 Up 23 user@R5> show isis adjacency Interface System L State Hold (secs) SNPA so-0/0/0.0 R6 2 Up 22 so-0/0/1.0 R1 2 Up 20 so-0/0/2.0 R4 1 Up 20 user@R6> show isis adjacency Interface System L State Hold (secs) SNPA so-0/0/0.0 R5 2 Up 21 so-0/0/2.0 R2 2 Up 20
The sample output shows the adjacencies that formed in the network illustrated in Figure 9. The Level 1/Level 2 routers (R2 and R5)formed Level 1 adjacencies with Level 1 routers (R3 and R4), and Level 2 adjacencies with the Level 2 routers (R1 and R6). To view the status of the adjacency, examine the State column. In this example, all adjacencies in the network are up.
If the state is not Up for a particular neighbor, you must first examine the IS-IS configuration for the particular interface. Make sure that the NET address is correct and that the loopback (lo0) interface is configured. Use the show isis interface or show isis interface detail command to display the IS-IS parameters for all interfaces configured with IS-IS. With these two commands, you can see which interfaces are configured for IS-IS, whether they are configured for Level 1 or Level 2, the IS-IS metric, and other IS-IS information.
You can determine the cost associated with a route and the selection of a route. In this step, the path from router R5 to R3 is examined in two situations. In the first example, all metrics in the network are set to the default of 10; in the second example, all metrics on a transit router (R6) are set to 5.
To examine a route in an IS-IS network, enter one or all of the following CLI commands:
- user@host> show route destination-prefix
- user@host> show route detail destination-prefix
- user@host> show isis route destination-prefix
Sample Output 1
The following sample output shows the route from R5 to R3 when all metrics across interfaces are set to the default of 10:
[edit protocols isis]
user@R6# show
level 1 disable;
interface so-0/0/0.0 {
level 2 metric 10;
}
interface so-0/0/2.0 {
level 2 metric 5;
}
interface fxp0.0 {
disable;
}
interface lo0.0;
Sample Output 2
The following sample output shows the route from R5 to R3 after the metric on R6 is changed from the default of 10 to 5:
user@R5> show route 10.0.0.3
inet.0: 28 destinations, 28 routes (28 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.0.0.3/32 *[IS-IS/18] 00:00:10, metric 25
> to 10.1.56.2 via so-0/0/0.0
user@R5> show route detail 10.0.0.3
inet.0: 28 destinations, 28 routes (28 active, 0 holddown, 0 hidden)
10.0.0.3/32 (1 entry, 1 announced)
*IS-IS Preference: 18
Level: 2
Next hop: 10.1.56.2 via so-0/0/0.0, selected
State: <Active Int>
Age: 4:57 Metric: 25
Task: IS-IS
Announcement bits (1): 0-KRT
AS path: I
user@R5> show isis route detail 10.0.0.3
IS-IS routing table Current version: L1: 250 L2: 257
Prefix L Version Metric Type Interface Via
10.0.0.3/32 2 257 25 int so-0/0/0.0 R6
Sample output 1 shows the cost for each route and the preferred next hop. In this example, there are two next hops, one through R1 and the other through R6. Both have an equal cost (30) to the destination. The cost is indicated in the Metric field. The preferred next hop is randomly chosen. In this case, the preferred next hop is through R1, interface so-0/0/1.0. In the output for the show route command, the selected next hop is indicated by a forward arrow (>). With the show route detail command, the next hop is indicated by the key word selected. The output for the show isis route command shows the selected interface and indicates that the IS-IS protocol is building the correct routing table from the link-state database.
After the metric on R6 is changed to a lower value, sample output 2 shows a different cost and next hop. With IS-IS, routes with lower total path metrics are preferred over those with higher path metrics. The path through R6 (so-0/0/0.0) is now lower (25) than the path through R1 (so-0/0/1.0) (30). In the output for the show route command, the lower cost (25) is indicated in the Metric field, and the preferred path is indicated by the forward arrow (>) and the keyword selected. The output for the show isis route command shows the selected interface and indicates that the IS-IS protocol is building the correct routing table from the link-state database.
In general, the output for the show route commands shows all active entries in the routing table. The information displayed includes the name of the routing table (inet.0), the number of destinations for which there are routes in the routing table (28), how the route was learned, and the route preference value, such as [IS-IS/18]. In addition, any metric associated with the route (metric 30), and the name of the interface through which the route was learned are displayed.
You can display the set of routes installed in the forwarding table to verify that the routing protocol process (rpd) has relayed the correct information into the forwarding table. This is especially important when there are network problems, such as connectivity. In this procedure, you verify that the routes displayed in Step 2 appear in the forwarding table for router R5.
To examine the forwarding table for a router, enter the following CLI command:
user@R5> show route forwarding-table
destination 10.0.0.3 Routing table: inet Internet: Destination Type RtRef Next hop Type Index NhRef Netif 10.0.0.3/32 user 0 10.1.15.0 ucst 285 7 so-0/0/1.0 user@R5> show route forwarding-table destination 10.0.0.3 Routing table: inet Internet: Destination Type RtRef Next hop Type Index NhRef Netif 10.0.0.3/32 user 0 10.1.56.0 ucst 281 9 so-0/0/0.0
The sample output shows the selected next hop between routers R5 and R3 sent from the inet routing table and installed into the forwarding table. The first instance shows the route through R1 and the second instance shows the route through R6. In both instances, the preferred route displayed in Step 2 is installed in the forwarding table.
In general, the sample output includes the destination address and destination type, the next-hop address and next-hop type, the number of references to the next hop, an index number into an internal next-hop database, and the interface used to reach the next hop.
You can examine the entire link-state database to obtain important information about the network. In this step, you verify that the key word Attached appears in the output of the Level 1 routers (R3 and R4) and the Level 1/Level 2 routers (R2 and R5).
To examine the link-state database for routers at different levels of the network, enter the following CLI command:
user@R1> show isis database IS-IS level 1 link-state database: 0 LSPs IS-IS level 2 link-state database: LSP ID Sequence Checksum Lifetime Attributes R1.00-00 0x1b 0xd4b5 583 L1 L2 R2.00-00 0x1d 0x1a4f 1131 L1 L2 R5.00-00 0x1b 0x6245 883 L1 L2 R6.00-00 0x20 0xf7c 919 L1 L2 4 LSPs user@R2> show isis database IS-IS level 1 link-state database: LSP ID Sequence Checksum Lifetime Attributes R2.00-00 0x56 0xbd8c 862 L1 L2 Attached R3.00-00 0x58 0xaca1 463 L1 2 LSPs IS-IS level 2 link-state database: LSP ID Sequence Checksum Lifetime Attributes R1.00-00 0x57 0x3e10 871 L1 L2 R2.00-00 0x5e 0x9790 1150 L1 L2 R5.00-00 0x5a 0xadba 1162 L1 L2 R6.00-00 0x56 0xa2b2 484 L1 L2 4 LSPs user@R3> show isis database IS-IS level 1 link-state database: LSP ID Sequence Checksum Lifetime Attributes R2.00-00 0x56 0xbd8c 792 L1 L2 Attached R3.00-00 0x58 0xaca1 397 L1 2 LSPs IS-IS level 2 link-state database: 0 LSPs [edit protocols isis] user@R4> show isis database IS-IS level 1 link-state database: LSP ID Sequence Checksum Lifetime Attributes R4.00-00 0x56 0x34b8 1125 L1 R5.00-00 0x57 0x22bb 795 L1 L2 Attached 2 LSPs IS-IS level 2 link-state database: 0 LSPs user@R5> show isis database IS-IS level 1 link-state database: LSP ID Sequence Checksum Lifetime Attributes R4.00-00 0x56 0x34b8 1071 L1 R5.00-00 0x57 0x22bb 745 L1 L2 Attached 2 LSPs IS-IS level 2 link-state database: LSP ID Sequence Checksum Lifetime Attributes R1.00-00 0x57 0x3e10 707 L1 L2 R2.00-00 0x5e 0x9790 982 L1 L2 R5.00-00 0x5a 0xadba 1002 L1 L2 R6.00-00 0x57 0xa0b3 1064 L1 L2 4 LSPs user@R6> show isis database IS-IS level 1 link-state database: 0 LSPs IS-IS level 2 link-state database: LSP ID Sequence Checksum Lifetime Attributes R1.00-00 0x1b 0xd4b5 728 L1 L2 R2.00-00 0x1c 0x1c4e 604 L1 L2 R5.00-00 0x1b 0x6245 1032 L1 L2 R6.00-00 0x20 0xf7c 1072 L1 L2 4 LSPs
The sample output shows the details of the Level 1 and Level 2 IS-IS databases for routers R1, R2, R3, R4, R5, and R6. Whether a router is configured for Level 1, Level 2 or Level 1/Level 2 is indicated by the type of IS-IS link-state datebase(s) in the output for the show isis database command for that router. For example, R3 and R4 are Level 1 routers because they do not have LSPs in the Level 2 link-state database, and the R1 and R6 are Level 2 routers because they do not have LSPS in the Level 1 link-state database. R2 and R5 are have LSPs in both Level 1/Level 2 link-state databases, indicating they are Level 1/Level 2 routers.
In addition, the output for R2 shows that it is a Level 1/Level 2 router because it has R3 in its Level 1 database, while R3 does not have the L2 notation in the Attributes field, indicating that it is configured for Level 1.
The details of the Level 2 IS-IS database are the same for all Level 2 routers in the network.
The key word Attached appears in the Level 1 link-state database for R2, R3, R4, and R5, indicating that the Level 2 routers (R2 and R5) can communicate with other Level 2 systems and act as gateways for the Level 1 routers (R3 and R4) in their respective areas. If the links that connect R2 and R5 to the other Level 2 routers (R1 and R6) are broken, the key word Attached will not appear in the output because R2 and R5 will no longer act as gateways for the Level 1 routers.
By using the key word extensive, you can examine each header field of a link-state protocol data unit (LSP) and gather important details about the network. In this step, you examine the IS-IS database for router R2.
To examine an LSP header, enter the following CLI command:
user@R2> show isis database extensive IS-IS level 1 link-state database:
[...Output truncated...]
Header: LSP ID: R2.00-00 , Length: 139 bytes
Allocated length: 1492 bytes, Router ID: 10.0.0.2
Remaining lifetime: 1071 secs, Level: 1 ,Interface: 0
Estimated free bytes: 1353, Actual free bytes: 1353
Aging timer expires in: 1071 secs
Protocols: IP, IPv6
Packet: LSP ID: R2.00-00, Length: 139 bytes, Lifetime : 1198 secs
Checksum: 0xbb8d, Sequence: 0x57, Attributes: 0xb <L1 L2 Attached>
NLPID: 0x83, Fixed length: 27 bytes, Version: 1, Sysid length: 0 bytes
Packet type: 18 , Packet version: 1, Max area: 0
[...Output truncated...]
Header: LSP ID: R3.00-00 , Length: 139 bytes
Allocated length: 284 bytes, Router ID: 10.0.0.3
Remaining lifetime: 823 secs, Level: 1 ,Interface: 68
Estimated free bytes: 145, Actual free bytes: 145
Aging timer expires in: 823 secs
Protocols: IP, IPv6
Packet: LSP ID: R3.00-00, Length: 139 bytes, Lifetime : 1198 secs
Checksum: 0xaaa2, Sequence: 0x59, Attributes: 0x1 <L1>
NLPID: 0x83, Fixed length: 27 bytes, Version: 1, Sysid length: 0 bytes
Packet type: 18, Packet version: 1, Max area: 0
[...Output truncated...]
IS-IS level 2 link-state database:
[...Output truncated...]
Header: LSP ID: R1.00-00, Length: 194 bytes
Allocated length: 284 bytes, Router ID: 10.0.0.1
Remaining lifetime: 398 secs, Level: 2 ,Interface: 67
Estimated free bytes: 145, Actual free bytes: 90
Aging timer expires in: 398 secs
Protocols: IP, IPv6
Packet: LSP ID: R1.00-00, Length: 194 bytes, Lifetime : 1196 secs
Checksum: 0x3e10, Sequence: 0x57, Attributes: 0x3 <L1 L2>
NLPID: 0x83, Fixed length: 27 bytes, Version: 1, Sysid length: 0 bytes
Packet type: 20 , Packet version: 1, Max area: 0
[...Output truncated...]
Header: LSP ID: R2.00-00 , Length: 236 bytes
Allocated length: 1492 bytes, Router ID: 10.0.0.2
Remaining lifetime: 677 secs, Level: 2 ,Interface: 0
Estimated free bytes: 1256, Actual free bytes: 1256
Aging timer expires in: 677 secs
Protocols: IP, IPv6
Packet: LSP ID: R2.00-00, Length: 236 bytes, Lifetime : 1198 secs
Checksum: 0x9790, Sequence: 0x5e, Attributes: 0x3 <L1 L2>
NLPID: 0x83, Fixed length: 27 bytes, Version: 1, Sysid length: 0 bytes
Packet type: 20, Packet version: 1, Max area: 0
[...Output truncated...]
The sample output is from router R2 and shows extensive information about the Level 1 and Level 2 link-state databases, which are identical across all Level 2 routers. Level 1 routers only include information for the Level 1 link-state database, which is identical to the Level 1 information in the output for a Level 2 router. The sample output shows the details of four LSPs. Level 1 and Level 2 LSPs include identical types of information except for the packet type. A Level 2 LSP has a packet type of 20 and a Level 1 LSP has a packet type of 18.
The first three examples illustrate different values in the Attributes field:
The fourth example, R2.00-00, is included to show that a Level 1/Level 2 router appears in both the Level 1 and the Level 2 link-state databases. Note that in the Level 2 link-state database, the key word Attached is not included in the Attributes field.
It is useful to examine one LSP in greater detail. The third LSP, R1.00-00, was originated by R1 as indicated by the LSP ID field. R1 is the hostname of the router. The first 00 indicates that the LSP is for the router itself, and the final 00 denotes that the LSP is not fragmented. Both IPv4 and IPv6 are supported by this router, as indicated in the Protocols field. The Attributes field shows that the router is capable of both Level 1 and Level 2 routing, is not connected to Level 1 routers in other areas, and is not overloaded. The key words Attached and Overloaded would appear in the Attributes field if this were the case. The remaining lifetime of the LSP is 1196 seconds. IS-IS lifetimes start at a configured age (1200 seconds by default) and count down to zero.