Description

The following Juniper documentation, lists a few options and details for show isis database output.

https://www.juniper.net/documentation/us/en/software/junos/cli-reference/topics/ref/command/show-isis-database.html

 

This knowledge article explains what additional information does show isis database output displays.

Symptoms

Information regarding show isis database

Solution

What are ISIS LSPs?

The IS-IS protocol is an interior gateway protocol (IGP) that uses link-state information to make routing decisions.  IS-IS evaluates the topology changes and determines whether to perform a full SPF recalculation or a partial route calculation (PRC).

All this link-state databases are flooded periodically throughout an area via Link State PDUs (also known as ISIS LSPs). ISIS LSPs Contain information about the state of adjacencies to neighboring IS-IS systems.

Each link-state PDU must be refreshed periodically on the network and is acknowledged by information within a sequence number PDU.

 

 

How is the Link-State Database Updated?

For a single LSDB, if there is any change in link properties, then the router, sends a new ISIS LSP with a new sequence number for the same LSP ID.

On point-to-point links, each link-state PDU is acknowledged by a partial sequence number PDU (PSNP), but on broadcast links, a complete sequence number PDU (CSNP) is sent out over the network. Any router that finds newer link-state PDU information in the CSNP then purges the out-of-date entry and updates the link-state database.

Link-state PDUs support variable-length subnet mask addressing.

 

 

How is the Link-State Database Identified?

Each LSP is identified by its <name>.<pseudonodeid>-<fragment-id>

Example- Router1.00-01

Router1 --> Node Name/ System Identifier/ Hostname

00 --> Pseudo Node ID

01 --> Fragment ID

 

 

Why is the ISIS LSP for a router in Fragmented?

Example, we have a router Router1 and it has multiple links connected to multiple routers. In this scenario, the ISIS LSP will be bigger in size, and hence will be fragmented into two parts. Two fragments of the same LSP ID.

labroot@Router1> show isis database | match R7 
Router1.00-00  0x1446  0x9925   1179 L1 L2 <<<<<< sequence number for fragment 00
Router1.00-01   0x97c  0x7570   584 L1 L2


Here 0x1446 represents the sequence number for the fragment Router1.00-00, and similarly, 0x97c represents the sequence number of the fragment Router1.00-01.

 

 

How to check the details of the ISIS LSP?

All the links' details will be present in either fragment. To check the details of ISIS LSPs, use the extensive option.

 

labroot@Router1> show isis database Router1 extensive 
Jun 18 04:58:34
IS-IS level 1 link-state database:

IS-IS level 2 link-state database:

Router1.00-00 Sequence: 0x1446, Checksum: 0x9925, Lifetime: 1160 secs
   IS neighbor: Router6.00       Metric:       10
     Two-way fragment: Router6.00-00, Two-way first fragment: Router6.00-00
   IS neighbor: Router8.00      Metric:       10
     Two-way fragment: Router8.00-00, Two-way first fragment: Router8.00-00
   IS neighbor: Router18.00        Metric: 16777214
     Two-way fragment: Router18.00-00, Two-way first fragment: Router18.00-00
   IS neighbor: Router19.00      Metric:       15
     Two-way fragment: Router19.00-00, Two-way first fragment: Router19.00-00
   IP prefix: 10.10.5.0/30                    Metric:       10 Internal Up
   IP prefix: 10.10.6.0/30                    Metric:       10 Internal Up
   IP prefix: 42.42.42.0/30                   Metric: 16777214 Internal Up
   IP prefix: 50.50.50.0/30                   Metric:       15 Internal Up
   IP prefix: 54.54.54.0/30                   Metric:       10 Internal Up
   IP prefix: 60.60.60.0/30                   Metric:       20 Internal Up
   IP prefix: 171.43.43.0/24                  Metric:      100 Internal Up
   IP prefix: 192.168.1.7/32                  Metric:        0 Internal Up
   V6 prefix: 2620:0:1cff:dead:beef:ffff:ffff:fd21/128 Metric:        0 Internal Up

  Header: LSP ID: Router1.00-00, Length: 560 bytes
    Allocated length: 1492 bytes, Router ID: 192.168.1.7
    Remaining lifetime: 1160 secs, Level: 2, Interface: 0
    Estimated free bytes: 600, Actual free bytes: 932
    Aging timer expires in: 1160 secs
    Protocols: IP, IPv6

  Packet: LSP ID: Router1.00-00, Length: 560 bytes, Lifetime : 1198 secs
    Checksum: 0x9925, Sequence: 0x1446, 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: 49.0001 (3)
    LSP Buffer Size: 1492
    Speaks: IP
    Speaks: IPV6
    IP router id: 192.168.1.7
    IP address: 192.168.1.7
    IPv6 TE Router ID: 2620:0:1cff:dead:beef:ffff:ffff:fd21
    Hostname: Router1
    Extended IS Reachability TLV, Type: 22, Length: 170
    IS extended neighbor: Router18.00, Metric: default 16777214 SubTLV len: 74
      IP address: 42.42.42.2
      Neighbor's IP address: 42.42.42.1
      Local interface index: 101, Remote interface index: 325
      Current reservable bandwidth:
        Priority 0 : 32Gbps
        Priority 1 : 32Gbps
        Priority 2 : 32Gbps
        Priority 3 : 32Gbps
        Priority 4 : 32Gbps
        Priority 5 : 32Gbps
        Priority 6 : 32Gbps
        Priority 7 : 32Gbps
      Maximum reservable bandwidth: 32Gbps
      Maximum bandwidth: 40Gbps
      Administrative groups:  0x8000 CONTINENTAL 
    IS extended neighbor: Router8.00, Metric: default 10 SubTLV len: 74         <<<<<<
      IP address: 10.10.6.1               <<<<<<
      Neighbor's IP address: 10.10.6.2                   <<<<<<
      Local interface index: 104, Remote interface index: 80
      Current reservable bandwidth:
        Priority 0 : 198Gbps
        Priority 1 : 198Gbps
        Priority 2 : 198Gbps
        Priority 3 : 198Gbps
        Priority 4 : 198Gbps
        Priority 5 : 181.993Gbps               <<<<<<
        Priority 6 : 181.993Gbps               <<<<<<
        Priority 7 : 181.993Gbps               <<<<<<
      Maximum reservable bandwidth: 200Gbps
      Maximum bandwidth: 200Gbps
      Administrative groups:  0x8000 CONTINENTAL 
    IP extended prefix: 192.168.1.7/32 metric 0 up
    IP extended prefix: 42.42.42.0/30 metric 16777214 up
    IP extended prefix: 171.43.43.0/24 metric 100 up
    IP extended prefix: 50.50.50.0/30 metric 15 up
    IP extended prefix: 54.54.54.0/30 metric 10 up
    IP extended prefix: 10.10.5.0/30 metric 10 up
    IP extended prefix: 10.10.6.0/30 metric 10 up
    IP extended prefix: 60.60.60.0/30 metric 20 up
    IPv6 prefix: 2620:0:1cff:dead:beef:ffff:ffff:fd21/128 Metric 0 Up
    Router Capability:  Router ID 192.168.1.7, Flags: 0x00
      IPv6 TE Router Id: 2620:0:1cff:dead:beef:ffff:ffff:fd21
  No queued transmissions

 

 

The TLVs contain the following-

  • local and remote IP address
  • The fragment in which this link properties reside,
  • Current reservable bandwidth
  • Maximum bandwidth
  • Maximum reservable bandwidth
  • Router ID
  • If the peer support wide metrics (IS extended)

 

 

Modification History

2024-06-26 : Article Created