IL (network protocol)

Internet Link

Communication protocol
Abbreviation	IL
Developer(s)	Bell Labs
OSI layer	Transport layer (4)

The Internet Link protocol or IL is a connection-based transport-layer protocol designed at Bell Labs originally as part of the Plan 9 operating system and is used to carry 9P. It is assigned the Internet Protocol number of 40. It is similar to TCP but much simpler.

Its main features are:

• Reliable datagram service
• In-sequence delivery
• Internetworking using IP
• Low complexity, high performance
• Adaptive timeouts

As of the Fourth Edition of Plan 9, 2003, IL is deprecated in favor of TCP/IP because it doesn't handle long-distance connections well. ^[1]

Header

IL header format

Offset	Octet	0								1								2								3
Octet	Bit	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
0	0	Version and header length								Type of service								Packet length
4	32	Identification																Fragment information
8	64	Time to live								Protocol								Header checksum
12	96	IP source
16	128	IP destination
20	160	Checksum including header																Packet length
24	192	Packet type								Special								Src port
28	224	Dst port																Sequence id↴
34	272	↪Acked sequence

structIPIL{bytevihl;/* Version and header length */bytetos;/* Type of service */bytelength[2];/* packet length */byteid[2];/* Identification */bytefrag[2];/* Fragment information */bytettl;/* Time to live */byteproto;/* Protocol */bytecksum[2];/* Header checksum */bytesrc[4];/* Ip source */bytedst[4];/* Ip destination */byteilsum[2];/* Checksum including header */byteillen[2];/* Packet length */byteiltype;/* Packet type */byteilspec;/* Special */byteilsrc[2];/* Src port */byteildst[2];/* Dst port */byteilid[4];/* Sequence id */byteilack[4];/* Acked sequence */};

See also

• Fast Local Internet Protocol

References

1. "Plan 9 — Fourth Edition Release Notes". Lucent Technologies. June 2003. Retrieved August 3, 2018. We are phasing out the IL protocol since it doesn't handle long-distance connections well (and long-distance networks don't handle it well, either). IL is still used by fs(4) but TCP has become the standard protocol for all other services.

Further reading

• Dave Presotto; Phil Winterbottom. "The IL protocol".—The original paper describing IL