Viewing the IS-IS Link-State Database

Problem

You want to look at each router's link-state database to make sure that all the IS-IS routers know about each other.

Solution

Use the show isis database command to view the contents of the link-state database:

	aviva@RouterG> show isis database
	 
IS-IS level 1 link-state database:
	LSP ID Sequence Checksum Lifetime Attributes
	RouterG.00-00 0x65 0xfa35 851 L1 L2 Attached
	RouterA.00-00 0x5e 0xf289 661 L1 L2

	RouterA.02-00 0x59 0xeda9 632 L1 L2
	 3 LSPs
	IS-IS level 2 link-state database:
	LSP ID Sequence Checksum Lifetime Attributes
	RouterH.00-00 0x61 0xa315 923 L1 L2
	RouterG.00-00 0x61 0x125e 741 L1 L2
	RouterG.02-00 0x5e 0x79f0 741 L1 L2
	 3 LSPs

 

Discussion

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, RouterG 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 RouterG 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 RouterG:

	aviva@RouterH> show isis database level 2
	IS-IS level 2 link-state database:
	LSP ID Sequence Checksum Lifetime Attributes
	RouterH.00-00 0x61 0xa315 988 L1 L2
	RouterG.00-00 0x61 0x125e 802 L1 L2
	RouterG.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:

	aviva@RouterG>  
show isis database extensive level 2 RouterH.00-00
	IS-IS level 2 link-state database:
	RouterH.00-00 Sequence: 0x62, Checksum: 0xa116, Lifetime: 1121 secs
	 IS neighbor: RouterG.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: RouterH.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: RouterH.00-00, Length: 134 bytes, Lifetime : 1198 secs
	 Checksum: 0xa116, Sequence: 0x62, Attributes: 0x3 
	 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: RouterH
	 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: RouterG.02, Internal, Metric: default 10
	 IS extended neighbor: RouterG.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:

	RouterH.00-00 Sequence: 0x62, Checksum: 0xa116, Lifetime: 1121 secs
	 IS neighbor: RouterG.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

RouterG has one IS-IS neighbor, RouterH, and the metric to reach this neighbor is 10 (the default). RouterG 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)

RouterH is in area 49.0030. The next two lines list the protocols that RouterH 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: RouterH

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 RouterH 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: RouterG.02, Internal, Metric: default 10
	IS extended neighbor: RouterG.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.