CLNP / ES-IS (P2)

Status: draft

Notes on CLNP (ISO 8473-1) and ES-IS (ISO 9542) (M7). The definitions are in crates/wpg-protocols/src/clnp.rs, the samples in templates/protocols/l3/clnp-*.wpg.yaml and templates/protocols/routing/esis-*.wpg.yaml. Both run directly over the OSI encapsulation.

PDUs, how they are reached, and samples

id	PDU	Samples
`clnp`	CLNP, every PDU type: DT (`0x1c`), MD (`0x1d`), ER (`0x01`), ERQ / ERP (`0x1e` / `0x1f`)	`clnp-dt` (segmentation part), `clnp-er` (reason for discard), `clnp-erq` (priority, source routing)
`esis_esh`	ES-IS End System Hello (2)	`esis-esh`
`esis_ish`	ES-IS Intermediate System Hello (4)	`esis-ish` (ES configuration timer)
`esis_rd`	ES-IS Redirect (6)	`esis-rd`
`esis`	Any ES-IS PDU: fixed part + opaque octets	`esis-generic`

dot3 / llc / clnp / payload        # DT carrying a transport PDU
dot3 / llc / clnp / raw            # ER carrying the discarded header
dot3 / llc / esis_esh              # to 09:00:2b:00:00:05 (AllIntermediateSystems)
dot3 / llc / esis_ish              # to 09:00:2b:00:00:04 (AllEndSystems)
ppp / clnp / payload               # PPP protocol 0x0023

The LLC DSAP / SSAP (0xfe) and the PPP protocol (0x0023) are Auto. When parsing, the NLPID 0x81 selects clnp and 0x82 the generic esis, whose pdu_type then re-decodes the layer as the dedicated PDU; unknown ES-IS types stay esis. PDUs shorter than the fixed part (CLNP 11 octets, ES-IS 9) decode as the generic osi.

The clnp layer is the header only. Its data (DT: the transport PDU; ER: the header of the discarded PDU; ERQ / ERP: the echoed PDU) is the next layer, typically payload or raw.

Auto fields

Field	Rule
`length_indicator`	Header length in octets (CLNP: up to the end of the options; ES-IS: the whole PDU)
`segment_length` (CLNP)	Length of the whole PDU (header + data)
`checksum`	ISO 8473 Fletcher checksum of the header (CLNP) / of the PDU (ES-IS). A Manual `0` means “checksum not used”; it is sent as is and reported as differing from Auto (a computed checksum is never 0)
`sp` (CLNP)	1 when the `segmentation` part has an element, else 0
`number_of_source_addresses` (ESH)	Number of `source_addresses`
`bsnpa_length` (RD)	Size of `bsnpa`

The CLNP segmentation part is a list of at most one {data_unit_identifier, segment_offset, total_length}; total_length (the length of the unsegmented PDU) is not computed:

- protocol: clnp
  fields:
    segmentation:
      - { data_unit_identifier: 1, segment_offset: 0, total_length: 69 }

Options

Options are {code, length, value} items after the addresses (and the segmentation part); they end at the length_indicator (Length::UntilOffset), so whatever follows the header is the next layer even though the addresses have variable size.

Code	Name (`name`)	Value fields	In
`0xc5`	`security`	`value` (octets)	CLNP, ES-IS
`0xc3`	`qos_maintenance`	`value` (octets)	CLNP, ES-IS
`0xcd`	`priority`	`value`	CLNP, ES-IS
`0xc8` / `0xcb`	`source_routing` / `recording_of_route`	`route_type` (`partial` / `complete`), `next_address`, `addresses`: list of `{address}`	CLNP
`0xcc`	`padding`	`data`	CLNP
`0xc1`	`reason_for_discard`	`reason` (`destination_unknown`, `lifetime_expired_in_transit`, …), `pointer`	CLNP (ER)
`0xe1` / `0xe2`	`address_mask` / `snpa_mask`	`mask`	ES-IS
`0xc6`	`es_configuration_timer`	`seconds`	ES-IS (ISH)

Other options are kept as { type: N, data: "..." }.

Limits

The segmentation total_length is not computed, and no segmentation / reassembly of a large PDU into several frames is done.
Security and quality of service maintenance values are octets; the globally unique / source address specific formats are not split.
A Redirect’s subnetwork address (bsnpa) is octets (a MAC address is 6 octets: "02 00 00 00 00 02"). An empty net ("") redirects to an end system.

Generated reference

Field reference of the protocols on this page (generated from the definitions):

osi · clnp · esis · esis_esh · esis_ish · esis_rd · payload · raw