ENL Protocol

ENL is Nintendo's private peer-to-peer framework that's used by many first-party games, such as Mario Kart 8, Splatoon 2 and Super Mario Maker 2. Check out the pages about PIA for details on how a peer-to-peer session is set up. Once the session is ready, ENL sends all packets through the unreliable protocol.

To transmit game-data, games can register content transporters to ENL. ENL also implements a few content transporters on its own.

A message consists of one or more records, terminated by a record with type 255. No byte swapping is done on the fields. The endianness depends on the system.

Record Header

Type	Description
Uint8	Record type
Uint16	Record size
Bytes	Record data

Record Type	Description
0 - 31	Game-specific
253	System request info
254	System information
255	End record

System request info

Clients can use this to request a specific record from another client. Every non-zero bit in the record mask indicates a record type that the client wants to receive. The least significant bit represents record type 0, and the most significant bit represents record type 31.

On the Switch, a new field was added that lets a client request a system-record. Here, bit 0 represents record type 253, and bit 1 represents record type 254.

Wii U:

Type	Description
Uint32	Record mask (games)

Switch:

Type	Description
Uint32	Record mask (games)
Uint32	Record mask (system)

System information

In the tables below, the values of P (maximum number of players) and Q (maximum number of CPUs) are configured by the game.

Game	P	Q
Mario Kart 8	14	10
Splatoon 2	10	0
Super Mario Maker 2	4	0

Wii U:

Type	Description
Uint32	Connected AID bitmap
Uint32	Disconnected AID bitmap
Uint32	CPU AID bitmap
Uint32	Received AID bitmap
Uint64	Session time at join
Uint32	Principal id
Uint32	Unknown
Uint8	Is player id table initialized
UniqueId (P*2-1)	Player unique ids
UniqueId (Q)	CPU unique ids
Uint8	Player id sync unique
Uint8 (P)	Player id table

Switch:

Type	Description
Uint64	Connected AID bitmap
Uint64	Disconnected AID bitmap
Uint64	CPU AID bitmap
Uint64	Received AID bitmap
Uint64	Session time at join
Uint64	Principal id
Uint8	Is player id table initialized
UniqueId (P*2-1)	Player unique ids
UniqueId (Q)	CPU unique ids
Uint8	Player id sync unique
Uint8 (P)	Player id table

UniqueId

Wii U:

Offset	Size	Description
0x0	4	Constant id
0x4	2	Unknown
0x6	2	Padding (always 0)

Switch:

Offset	Size	Description
0x0	8	Constant id
0x8	1	Is local player
0x9	1	Is disconnected
0xA	6	Padding (always 0)