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Show the IS-IS Link-State Database
 
You want to look at each router's link-state database to make sure that all the IS-IS routers know about each other.
Use the show isis database command to view the contents of the link-state database:
 
source@RouterA> show isis database
 
IS-IS level 1 link-state database:
LSP ID                      Sequence Checksum Lifetime Attributes
RouterA.00-00                   0x65   0xfa35      851 L1 L2 Attached
RouterC.00-00                   0x5e   0xf289      661 L1 L2
 
RouterC.02-00                   0x59   0xeda9      632 L1 L2
  3 LSPs
IS-IS level 2 link-state database:
LSP ID                      Sequence Checksum Lifetime Attributes
RouterC.00-00                   0x61   0xa315      923 L1 L2
RouterA.00-00                   0x61   0x125e      741 L1 L2
RouterA.02-00                   0x5e   0x79f0      741 L1 L2
  3 LSPs
 
IS-IS routers exchange LSPs that describe each individual router's view of the network topology and they store the LSPs in a link-state database. The SPF algorithm then runs on the link-state database to create the IS-IS routing table. Use the show isis database command to look at the contents of the link-state database. In this recipe, RouterA is a Level 1Level 2 router, so you see two link-state databases, one for each level.
 
The first part of the output shows that the Level 1 link-state database has three LSPs. The entry for RouterA includes the attach bit (Attached), which indicates that it is connected to another IS-IS area. From the configuration, you know that this router is connected to area 30.
 
If you check on the other Level 2 router, its Level 2 database is identical to that of RouterA:
 
source@RouterC> show isis database level 2
IS-IS level 2 link-state database:
LSP ID                      Sequence Checksum Lifetime Attributes
RouterC.00-00                   0x61   0xa315      988 L1 L2
RouterA.00-00                   0x61   0x125e      802 L1 L2
RouterA.02-00                   0x5e   0x79f0      802 L1 L2
  3 LSPs
 
Use the extensive version of the show isis database command to see all the information carried in the LSP:
 
source@RouterA> show isis database extensive level 2 RouterC.00-00
IS-IS level 2 link-state database:
RouterC.00-00 Sequence: 0x62, Checksum: 0xa116, Lifetime: 1121 secs
   IS neighbor: RouterA.02                    Metric:       10
   IP prefix: 10.0.1.0/24                     Metric:       10 Internal Up
   IP prefix: 10.0.24.0/24                    Metric:       10 Internal Up
  Header: LSP ID: RouterC.00-00, Length: 134 bytes
    Allocated length: 284 bytes, Router ID: 192.168.18.1
    Remaining lifetime: 1121 secs, Level: 2,Interface: 64
    Estimated free bytes: 170, Actual free bytes: 150
    Aging timer expires in: 1121 secs
    Protocols: IP, IPv6
  Packet: LSP ID: RouterC.00-00, Length: 134 bytes, Lifetime : 1198 secs
    Checksum: 0xa116, Sequence: 0x62, 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
 
  TLVs:
    Area address: 49.0030 (3)
    Speaks: IP
    Speaks: IPv6
    IP router id: 192.168.18.1
    IP address: 192.168.18.1
    Hostname: RouterC
    IP prefix: 10.0.24.0/24, Internal, Metric: default 10, Up
    IP prefix: 10.0.1.0/24, Internal, Metric: default 10, Up
    IP extended prefix: 10.0.24.0/24 metric 10 up
    IP extended prefix: 10.0.1.0/24 metric 10 up
    IS neighbor: RouterA.02, Internal, Metric: default 10
    IS extended neighbor: RouterA.02, Metric: default 10
      IP address: 10.0.1.1
  No queued transmissions
 
The first section of the output shows the entries (IS-IS neighbors and IP prefixes) in the link-state database:
 
RouterC.00-00 Sequence: 0x62, Checksum: 0xa116, Lifetime: 1121 secs
   IS neighbor: RouterA.02                    Metric:       10
   IP prefix: 10.0.1.0/24                     Metric:       10 Internal Up
   IP prefix: 10.0.24.0/24                    Metric:       10 Internal Up
 
RouterA has one IS-IS neighbor, RouterC, and the metric to reach this neighbor is 10 (the default). RouterA has learned two prefixes, both from a Level 1 (internal) IS-IS area, and both prefixes have the default metric cost of 10. Any routes learned from outside the area would be marked External.
 
The remaining three sections correspond to portions of the LSP. The Header section shows the packet length, the router ID (which is the address configured on the lo0 interface), and various timer information. The Packet section shows the PDU length, remaining lifetime, checksum, sequence number, and other information. The TLV section shows the TLV information carried in the LSP. The first line shows TLV 1, the address of the area in which the router is located:
 
Area address: 49.0030 (3)
 
RouterC is in area 49.0030. The next two lines list the protocols that RouterC supports (TLV 129):
 
Speaks: IP
Speaks: IPv6
 
The router is running both IPv4 and IPv6. Next, you see two router IDs:
 
IP router id: 192.168.18.1
IP address: 192.168.18.1
 
The first line corresponds to TLV 134, the traffic-engineering router ID (defined in RFC 3784), and the second is TLV 132, which is defined as the interface address. In the JUNOS IS-IS implementation, the IP address field shows the configured router ID, not all interface addresses. The sixth line shows the router's dynamic (symbolic) hostname:
 
Hostname: RouterC
 
The next four lines show the IP prefixes in the LSP:
 
IP prefix: 10.0.24.0/24, Internal, Metric: default 10, Up
IP prefix: 10.0.1.0/24, Internal, Metric: default 10, Up
IP extended prefix: 10.0.24.0/24 metric 10 up
IP extended prefix: 10.0.1.0/24 metric 10 up
 
The first two prefixes map to TLV 128, IP internal reachability, and are the IP addresses within the routing domain that are directly reachable through RouterC interfaces. This TLV can carry metrics in the range of 0 through 63. The second two prefixes map to TLV 135, the extended reachability TLV, defined in RFC 3784. This TLV can carry metric values greater than 63.
 
The last two lines provide information about reaching IS-IS neighbors:
 
IS neighbor: RouterA.02, Internal, Metric: default 10
IS extended neighbor: RouterA.02, Metric: default 10
 IP address: 10.0.1.1
 
The first line, IS neighbor, corresponds to TLV 2, which carries IS reachability information, including the one-octet default metric. The second line maps to TLV 22, for extended IS reachability information (also defined in RFC 3784). This TLV carries three-octet metric values.
 
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