ISO 10589
Intermediate System to Intermediate System Protocol
Level-1 LAN IS-IS Hello
Level-2 LAN 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.
Level-1/2 LAN 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: Level-1/2 LAN 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: Level-1/2 LAN IS-IS Hello / Fixed Part
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: Level-1/2 LAN 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: Level-1/2 LAN IS-IS Hello / Fixed Part
Field: PDU length
Length: 2 bytes
Contents: length of the PDU in bytes.
Priority (7 bits)
Protocol: ISO 10589 / IS-IS
PDU Part: Level-1/2 LAN IS-IS Hello / Fixed Part
Field: priority
Length: 7 bits
Contents: priority value.
The priority value determines whether the IS will operate as designated IS.
The first bit of this octet is unused.
LAN ID (n bytes)
Protocol: ISO 10589 / IS-IS
PDU Part: Level-1/2 LAN IS-IS Hello / Fixed Part
Field: LAN ID
Length: n bytes
Contents: idetifies the designated IS.
This field's length is calculatedas [ID Length] + 1 byte.
Area Addresses (n bytes)
Protocol: ISO 10589 / IS-IS
PDU Part: Level-1/2 LAN IS-IS Hello / Variable Part
Field: area addresses
Length: n bytes
Contents: one or more area addresses of this IS.
IS Neighbors (n bytes)
Protocol: ISO 10589 / IS-IS
PDU Part: Level-1/2 LAN IS-IS Hello / Variable Part
Field: IS neighbors
Length: n bytes
Contents: one or more addresses of a neighbor IS.
Padding (0-n bytes)
Protocol: ISO 10589 / IS-IS
PDU Part: Level-1/2 LAN IS-IS Hello / Variable 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: Level-1/2 LAN IS-IS Hello / Variable Part
Field: authentication information
Length: n bytes
Contents: password for source station authentication.
This parameter is optional used for protection of the routing information.