IS-IS TLV

Type, Length, Value (TLV) Tuples

  • This is the true magic of IS-IS. Provides the ability to support multiple protocols in the same architecture.
  • TLVs provide variable modules, and support nesting.
  • A TLV is assigned a numerical value which directly correlates to a function.
  • When a router receives a IS PDU and detects an unrecognizable TLV, it just skips the TLV and continues to the next TLV in that packet.
  • TLVs are not modified in transit.

Common LSP TLVs

TLV # Function

  • 1 List of area addresses on router
  • 2 List of IS Neighbors (Narrow Metrics)
  • 10 Authentication
  • 22 Extended IS Neighbors (Wide Metrics)
  • 128 IP network and metric from advertising router (Narrow Metrics)
  • 130 External networks and metrics when redistributed
  • 132 IP Addresses on transmitting interface (includes secondary interfaces) (Narrow Metrics)
  • 135 IP Addresses on transmitting interface (includes secondary interfaces) (Wide Metrics)
  • 137 Router hostname (Allows correlation of name to System ID
  • 232 IPv6 Interface Address
  • 236 IPv6 Reachability Information
  • 237 Multi Topology Reachable IPv6 Prefix

source: Cisco

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