ISO 10589
Intermediate System to Intermediate System Protocol
Level-1 Partial Sequence Numbers
Level-2 Partial Sequence Numbers
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IS-IS is a routing protocol used between intermediate systems (IS = router) / router exchange protocol.
IS-IS is used in nine different PDU types:
> Point-to-point IS-IS hello
> Level-1 LAN IS-IS hello
> Level-2 LAN IS-IS hello> Level-1 link state
> Level-2 link state
> Level-1 complete sequence numbers
> Level-2 complete sequence numbers
> Level-1 partial sequence numbers
> Level-2 partial sequence numbers
All PDU types use the same 'common part' at the beginning of the PDU; the parameters after 'common part' differ.
There are four different routing-level:
Level-0 Routing: between ESs and ISs in the same subnet.
Level-1 Routing: between ISs within the same ares.
Level-2 Routing: between different areas within the same routing domain.
Level-3 Routing: between different routing domains.
Level-1/2 Partial Sequence Numbers uses a fixed part first and a variable part behind it.
PDU Length (2 bytes)
Protocol: ISO 10589 / IS-IS
PDU Part: Level-1/2 Partial Sequence Numbers / Fixed Part
Field: PDU length
Length: 2 bytes
Contents: length of PDU in bytes.
Source ID (n bytes)
Protocol: ISO 10589 / IS-IS
PDU Part: Level-1/2 Partial Sequence Numbers / Fixed Part
Field: source ID
Length: n bytes
Contents: address of the sending IS.
The source ID length is calculated as: [ID Length] + 1 byte.
LSP Entries (n bytes)
Protocol: ISO 10589 / IS-IS
PDU Part: Level-1/2 Partial Sequence Numbers / Fixed Part
Field: LSP entries
Length: n bytes
Contents: LSP entries.
List of LSP entries in incrementing order of IDs. Each entry contains:
> LSP ID
> Remaining Lifetime
> LSP Sequence Number
> Checksum.
Authentication Information (n bytes)
Protocol: ISO 10589 / IS-IS
PDU Part: Level-1/2 Partial Sequence Numbers / Fixed Part
Field: authentication information
Length: n bytes
Contents: password for source station authentication.
This parameter is optional used for protection of the routing information.