IS-IS (`isis`)

Layer: L3 (network)
Header: variable length
Notes: IS-IS (P2)

Reached from

Lower layer	Selector	Value
`llc`	First 8 bits of the payload when `dsap` = 254 (0xfe)	131 (0x83)
`ppp`	First 8 bits of the payload when `protocol` = 35 (0x0023)	131 (0x83)

Fields

Field	Type	Default	Auto	Description
`irpd`	`enum(8)`	`131` (isis)		Intradomain routing protocol discriminator (0x83 = IS-IS).
`header_length`	`uint(8)`	`27`		Length of the fixed header in octets (constant for each PDU type: LAN Hello / LSP 27, P2P Hello 20, CSNP 33, PSNP 17).
`version_ext`	`uint(8)`	`1`		Version / protocol ID extension (1).
`id_length`	`uint(8)`	`0`		System ID length (0 = 6 octets).
`reserved`	`uint(3)`	`0`
`pdu_type`	`enum(5)`	`15` (l1_lan_hello)		PDU type (15/16 LAN Hello L1/L2, 17 P2P Hello, 18/20 LSP L1/L2, 24/25 CSNP, 26/27 PSNP).
`version`	`uint(8)`	`1`		Version (1).
`reserved2`	`uint(8)`	`0`
`max_area_addresses`	`uint(8)`	`0`		Maximum number of area addresses (0 = 3).
`data`	`bytes` — rest of the PDU	`""`		Rest of the PDU after the common header (opaque octets).

`irpd`

Value	Name
131 (0x83)	`isis`

`pdu_type`

Value	Name
15	`l1_lan_hello`
16	`l2_lan_hello`
17	`p2p_hello`
18	`l1_lsp`
20	`l2_lsp`
24	`l1_csnp`
25	`l2_csnp`
26	`l1_psnp`
27	`l2_psnp`

Next layer

The next layer is selected by pdu_type; when the field is Auto the builder writes the value of the protocol stacked above.

Value	Protocol	Note
15	`isis_l1_lan_hello`	re-decodes this layer
16	`isis_l2_lan_hello`	re-decodes this layer
17	`isis_p2p_hello`	re-decodes this layer
18	`isis_l1_lsp`	re-decodes this layer
20	`isis_l2_lsp`	re-decodes this layer
24	`isis_l1_csnp`	re-decodes this layer
25	`isis_l2_csnp`	re-decodes this layer
26	`isis_l1_psnp`	re-decodes this layer
27	`isis_l2_psnp`	re-decodes this layer

Sample templates

isis-generic — templates/protocols/routing/isis-generic.wpg.yaml