GRE (`gre`)

Layer: L3 (network)
Header: 4 octets (fixed)
Notes: Encapsulation and tunnels

Reached from

Lower layer	Selector	Value
`ipv4`	`protocol`	47 (0x2f)
`ipv6`	`next_header`	47 (0x2f)
`ipv6_hopopts`	`next_header`	47 (0x2f)
`ipv6_route`	`next_header`	47 (0x2f)
`ipv6_srh`	`next_header`	47 (0x2f)
`ipv6_frag`	`next_header`	47 (0x2f)
`ipv6_dstopts`	`next_header`	47 (0x2f)

Fields

Field	Type	Default	Auto	Description
`flags`	`flags(16)`	`0x0`		GRE flags and version (checksum / key / sequence present bits).
`protocol_type`	`enum(16)`	`2048` (ipv4)	Protocol number of the next layer (see Next layer)	EtherType of the encapsulated payload.

`flags`

Bit	Mask	Name
15	32768 (0x8000)	`checksum_present`
13	8192 (0x2000)	`key_present`
12	4096 (0x1000)	`sequence_present`

`protocol_type`

Value	Name
2048 (0x0800)	`ipv4`
34525 (0x86dd)	`ipv6`
25944 (0x6558)	`transparent_ethernet`
34887 (0x8847)	`mpls`

Next layer

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

Value	Protocol	Note
2048 (0x0800)	`ipv4`
34525 (0x86dd)	`ipv6`
25944 (0x6558)	`ethernet2`
34887 (0x8847)	`mpls`

Sample templates

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