Assigned Network Numbers
A 1976 registry of network numbers for early ARPANET experiments.
Postel, J., "Assigned Network Numbers", RFC 717, DOI 10.17487/RFC0717, July 1976, <https://www.rfc-editor.org/info/rfc717>.
@misc{rfc717,
series = {Request for Comments},
number = 717,
howpublished = {RFC 717},
publisher = {RFC Editor},
doi = {10.17487/RFC0717},
url = {https://www.rfc-editor.org/info/rfc717},
author = {J. Postel},
title = {{Assigned Network Numbers}},
pagetotal = 1,
year = 1976,
month = jul,
} RFC text
NWG/RFC# 717 JBP 30-JUN-76 16:58 35873
Assigned Network Numbers
Network Working Group Jon Postel
Request for Comments 717 SRI-ARC
NIC 35873 1 July 1976
Assigned Network Numbers
This note specifies the numbers assigned to identify networks for use in
the inter-network protocol experiments. Additional Numbers are assigned
by Jon Postel [POSTEL@ISIC or (415) 326-6200 x3718].
Assigned Network Numbers
Name Decimal Octal
---------- ------- -----
BBNRCCnet 3 3
SanFranPRnet 7 7
ARPANET 10 12
BostonPRnet 11 13
Internetwork Header Format
For convenience the current Internetwork protocol header and TCP
headers are reproduced here:
Octet Bit Use (Width)
--- Beginning of protocol-independent information ---
0 Destination net (8)
1-3 Destination host (24)
4 Source net (8)
5-7 Source host (24)
8-9 Data length in octets (16)
10 Header length in octets (8)
11 0-3 Format (4)
This field selects the appropriate gateway processing and is used
to dispatch the packet to the appropriate protocol module in the
destination. The following values are defined for this field:
0 -- Escape; protocol is specified by a subsequent field
1 -- TCP
2 -- Secure TCP
3-16 -- Not allocated
17 -- Cross internet debugging
--- End of protocol-independent information
1
NWG/RFC# 717 JBP 30-JUN-76 16:58 35873
Assigned Network Numbers
--- Beginning of TCP specific information ---
11 4-7 Protocol version (4)
12-15 Sequence number (32)
16-17 Window (16)
18-20 Control (as before) (24)
21-23 Destination port (24)
24 Packet label for debugging(8)
25-27 Source port (24)
28-31 Acknowledgement number (32)
32-33 Checksum (16)
34- Data
--- End of TCP specific information ---
--- Beginning of short TCP specific information ---
11 4-7 Protocol Version (4)
12-25 Sequence number (32)
16 Destination KID (8)
17 Source KID (8)
18-19 Control (no special function field)(16)
20- Data
--- End of short TCP specific information ---
2
AI ELI5
On this page
§1Network Number Registry
RFC 717 assigns identifying numbers to networks participating in early ARPANET inter-network protocol experiments. The assignment authority was Jon Postel at SRI-ARC. Four networks are listed: BBNRCCnet (3), SanFranPRnet (7), ARPANET (10), and BostonPRnet (11). These numbers served to uniquely identify each network in the experimental internet.
Networks needed numbers just like houses need addresses. This document gave out numbers to different research networks.
§2Network and Host Addressing
The Internetwork header format used 8 bits for the destination network and 24 bits for the destination host address, with the same structure for source addresses. This meant a maximum of 256 networks could be identified and 16 million hosts per network. The total header overhead for routing information was 8 octets.
Each address had two parts: which network, and which computer on that network.
§3Protocol Header Structure
The header included a Format field in bits 0-3 that identified which protocol was being used, allowing the packet to be routed to the correct protocol handler. Protocol values were defined as 1 for TCP, 2 for Secure TCP, and 17 for Cross Internet Debugging. The TCP-specific portion included sequence numbers, window size, control flags, and port numbers for application identification.
The header told routers which protocol to use (like choosing between email or chat), and included sending/receiving ports.