What is the proper classification of an IS-IS link state PDU?

Here are some suggestions:

Cell: Not applicable because TLVs are used. A cell must have a fixed length, according to ITU-T I.113 1997-06 and RFC3985.

Datagram: According to RFC1983, a datagram carries enough information to be routed from source to destination without depending on earlier exchanges between that source and destination. But IS-IS LSP are only communicated between intermediate systems.

Frame: According to ITU-T I.113 1997-06, a frame is a block of variable length at L2. However, since IS-IS is encapsulated by a L2 protocol, it seems redundant.

Message: Way too ambiguous. Sometimes a message is an opcode of an application layer protocol. Sometimes a message is defined by setting a flag (control bit).

Packet: Not applicable because according to ITU-T I.113 1997-06, a packet resides at L3.

Segment: Not applicable because it is connectionless. A segment is a packet that contains TCP/IP data or an acknowledgement, according to RFC5681. Apart from TCP, a segment implies sequence numbering.

  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer.
    – Ron Maupin
    Feb 19 '18 at 19:53
  • No, there is none. Feb 24 '18 at 9:44

IS-IS is an application running on top of layer 2. The standard calls the data entities just PDU (e.g. LSP = Link State PDU).

  • The standard does not define the term. As RFC1208 says, a PDU is a data object exchanged by protocol entities within a given layer. Oct 29 '17 at 7:23

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