GTP-U (`gtpu`)

Layer: L4 (transport)
Header: 8 octets (fixed)
Notes: Encapsulation and tunnels

Reached from

Lower layer	Selector	Value
`udp`	`dst_port` / `src_port`	2152 (0x0868)

Fields

Field	Type	Default	Auto	Description
`version`	`uint(3)`	`1`		GTP version (1).
`protocol_type`	`uint(1)`	`1`		Protocol type (1 = GTP, 0 = GTP’).
`spare`	`uint(1)`	`0`
`e_flag`	`uint(1)`	`0`		Extension-header-present flag.
`s_flag`	`uint(1)`	`0`		Sequence-number-present flag.
`pn_flag`	`uint(1)`	`0`		N-PDU-number-present flag.
`message_type`	`enum(8)`	`255` (g_pdu)		GTP-U message type (255 = G-PDU).
`length`	`uint(16)`		Length of the payload in octets	Length of the payload after the mandatory header, in octets (Auto).
`teid`	`uint(32)`	`0`		Tunnel Endpoint Identifier.

`message_type`

Value	Name
1 (0x01)	`echo_request`
2 (0x02)	`echo_response`
26 (0x1a)	`error_indication`
31 (0x1f)	`supported_extension_headers`
254 (0xfe)	`end_marker`
255 (0xff)	`g_pdu`

Next layer

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

First 4 bits of the payload when message_type = 255 (0xff)

Value	Protocol
4	`ipv4`
6	`ipv6`

Sample templates

gtpu-ipv4 — templates/protocols/encap/gtpu-ipv4.wpg.yaml