Official change in Host-Host Protocol
A protocol correction that assigns separate ERR codes to distinct error cases.
Krilanovich, M., "Official change in Host-Host Protocol", RFC 695, DOI 10.17487/RFC0695, July 1975, <https://www.rfc-editor.org/info/rfc695>.
@misc{rfc695,
series = {Request for Comments},
number = 695,
howpublished = {RFC 695},
publisher = {RFC Editor},
doi = {10.17487/RFC0695},
url = {https://www.rfc-editor.org/info/rfc695},
author = {M. Krilanovich},
title = {{Official change in Host-Host Protocol}},
pagetotal = 3,
year = 1975,
month = jul,
} RFC text
NWG/RFC# 695 MCK 5-JUL-75 15:38 32908
Official Change in Host-Host Protocol
Mark Krilanovich 1
Official Change in Host-Host Protocol 2
This is an official change to the Host to Host
protocol, this document should be filed with the
protocol specification (nic -- 8246,) in the Current
Network Protocols Notebook (nic -- 7104,). 3
-- Jon Postel 3a
This document corrects an ambiguity in the current
host-host protocol, concerning the ERR command.
Paragraph "f", page 35, of NIC 8246 defines the
meaning of an ERR command with error code of 5 to be
"socket (link) not connected". The error code is
stated to apply to two cases, one in which a control
command other than STR or RTS refers to a socket that
is neither fully open nor fully closed, and the other
in which a (non-control) message arrives over a link
not being used for a connection. 4
The difficulty arises from the fact that the contents
of the "data" field of the ERR command has distinctly
different formats in the two cases. In the first, it
is a host-host command, and in the second it is a
message header. There is no reliable way for the code
in the NCP receiving the ERR command (or a human
reviewing an error log) to distinguish between the two
cases, and therefore fullest use cannot be made of the
ERR command. 5
The two cases are now defined to have different error
codes. In addition, a new error code is defined,
meaning "invalid host leader received". Therefore,
paragraph "f" under "ERR - Error detected" is now
replaced by the following: 6
f. Request on a non-open socket (Error code = 5) 7
NWG/RFC# 695 MCK 5-JUL-75 15:38 32908
Official Change in Host-Host Protocol
A request other than an STR or RTS was made for a
socket (perhaps referenced by link number) that is
not party to an fully established connection. The
socket's inappropriate state could either be that
only one RFC has been sent (not yet open) or that
only one CLS has been sent (not yet closed). The
"data" field contains the command in error; the
value of any fill necessary is zeros. 7a
g. Message on an unknown link (Error code = 6) 8
A message was received over a user link which is
not currently being used for any connection. The
contents of the "data" field are the message header
followed by the first eight bits of text, if any,
or zeros. 8a
h. Invalid host header (Error code = 7) 9
A message was received either over the control link
or a valid user link that had a host header with
invalid format. Examples of when this subtype would
be appropriate are the following: the M1 or M2
fields were non-zero, the byte size was invalid
(not 8 for a control link, zero for any link), or
the declared length (byte size times byte count)
exceeded the actual length. The contents of the
"data" field is the message header padded with
eight bits of zeros. 9a
------- 10
1
ISO Plain Language
On this page
§1Why Error Code 5 Was Ambiguous
The earlier protocol used ERR code 5 for both a control command referring to a socket that was not fully open or closed and a non-control message arriving on a link not used for a connection.
The data field held a command in the first case and a message header in the second. A receiving NCP or a person reading an error log could not reliably distinguish them.
One error number described two different problems. Their data had different formats, but the number alone did not show which problem occurred.
§2The New Error-Code Meanings
The replacement text assigns error code 5 to a request other than STR or RTS on a socket that is not part of a fully established connection. Code 6 means a message arrived over a user link not currently used by a connection.
Code 7 means a message on the control link or a valid user link had an invalid host header. The RFC gives examples such as invalid M1 or M2 fields, invalid byte size, or a declared length greater than the actual length.
Each of the three error codes now identifies one case. The receiver can interpret the accompanying command or message header using the code.
§3Effect of the Change
The memo replaces paragraph f under “ERR - Error detected” in the Host-Host Protocol. The data field for each new code is defined for its corresponding case, including any zero fill described in the replacement text.
This is an official change to be filed with the protocol specification and the Current Network Protocols Notebook.
The memo replaces the ambiguous paragraph in the protocol documentation. It makes the ERR command's data easier to interpret.