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]

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

struct IPIL
{
    byte    vihl;       /* Version and header length */
    byte    tos;        /* Type of service */
    byte    length[2];  /* packet length */
    byte    id[2];      /* Identification */
    byte    frag[2];    /* Fragment information */
    byte    ttl;        /* Time to live */
    byte    proto;      /* Protocol */
    byte    cksum[2];   /* Header checksum */
    byte    src[4];     /* Ip source */
    byte    dst[4];     /* Ip destination */
    byte    ilsum[2];   /* Checksum including header */
    byte    illen[2];   /* Packet length */
    byte    iltype;     /* Packet type */
    byte    ilspec;     /* Special */
    byte    ilsrc[2];   /* Src port */
    byte    ildst[2];   /* Dst port */
    byte    ilid[4];    /* Sequence id */
    byte    ilack[4];   /* Acked sequence */
};

References

^ "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.

IL (network protocol)

Header

See also

References

Further reading