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NWG/RFC# 695                       MCK 5-JUL-75 15:38  32908Official Change in Host-Host Protocol                                      Mark Krilanovich     1         Official Change in Host-Host Protocol             2This is an official change to the Host to Hostprotocol, this document should be filed with theprotocol specification (nic -- 8246,) in the CurrentNetwork Protocols Notebook (nic -- 7104,).                 3                                         -- Jon Postel    3aThis document corrects an ambiguity in the currenthost-host protocol, concerning the ERR command.Paragraph "f", page 35, of NIC 8246 defines themeaning of an ERR command with error code of 5 to be"socket (link) not connected".  The error code isstated to apply to two cases, one in which a controlcommand other than STR or RTS refers to a socket thatis neither fully open nor fully closed, and the otherin which a (non-control) message arrives over a linknot being used for a connection.                           4The difficulty arises from the fact that the contentsof the "data" field of the ERR command has distinctlydifferent formats in the two cases.  In the first, itis a host-host command, and in the second it is amessage header.  There is no reliable way for the codein the NCP receiving the ERR command (or a humanreviewing an error log) to distinguish between the twocases, and therefore fullest use cannot be made of theERR command.                                               5The two cases are now defined to have different errorcodes.  In addition, a new error code is defined,meaning "invalid host leader received".  Therefore,paragraph "f" under "ERR - Error detected" is nowreplaced by the following:                                 6f.  Request on a non-open socket (Error code = 5)          7

NWG/RFC# 695                       MCK 5-JUL-75 15:38  32908Official 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.                  7ag.  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.                                              8ah.  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