ISO 10589
Intermediate System to Intermediate System Protocol
Point-to-Point IS-IS Hello
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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.
Point-to-Point IS-IS Hello uses a fixed part first and a variable part behind it.
Reserved / Circuit Type (1 byte)
Protocol: ISO 10589 / IS-IS
PDU Part: Point-to-Point IS-IS Hello / Fixed Part
Field: Reserved / Circuit Type
Length: 1 byte
Contents: type of use (Level-1/Level-2).
Indicates whether the IS will use this hop only for Level-1 traffic, only for Level-2 traffic or for both Level-1 and Level-2 traffic.
Source ID (n bytes)
Protocol: ISO 10589 / IS-IS
PDU Part: Point-to-Point IS-IS Hello / Fixed Part
Field: Source ID
Field: source ID
Length: n bytes
Contents: source address of the sending IS.
Since the source IDs vary in length, the current length must be indicated within the previous 'ID length' field (common part).
Holding Time (2 bytes)
Protocol: ISO 10589 / IS-IS
PDU Part: Point-to-Point IS-IS Hello / Fixed Part
Field: holding time
Length: 2 bytes
Contents: maximum precessing time.
The holding time indicates the maximum time an intermediate system (IS) may take to process the current PDU.
PDU Length (2 bytes)
Protocol: ISO 10589 / IS-IS
PDU Part: Point-to-Point IS-IS Hello / Fixed Part
Field: PDU length
Length: 2 bytes
Contents: length of PDU in bytes.
Local Circuit ID (1 byte)
Protocol: ISO 10589 / IS-IS
PDU Part: Point-to-Point IS-IS Hello / Fixed Part
Field: local circuit ID
Length: 1 byte
Contents: local ciruit ID.
Area Addresses (n bytes)
Protocol: ISO 10589 / IS-IS
PDU Part: Point-to-Point IS-IS Hello / Fixed Part
Field: area addresses
Length: n bytes
Contents: one ore more area addresses of this IS.
Padding (0-n bytes)
Protocol: ISO 10589 / IS-IS
PDU Part: Point-to-Point IS-IS Hello / Fixed Part
Field: Padding
Length: 0-n bytes
Contents: used for PDU alignment.
All PDUs have to be aligned to a standard length.
Authentication Information (n bytes)
Protocol: ISO 10589 / IS-IS
PDU Part: Point-to-Point IS-IS Hello / 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.