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.

Header

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 */
};

See also

• Fast Local Internet Protocol

Further reading

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