infopath@well.UUCP ("Jay W. Melvin") (01/02/91)
Greetings, and thanks in advance to anyone willing and able to address this
question.
BACKGROUND: I am implementing ICMP for the first time and need clarification
on the topic of Error_to_Source messages.
ISSUE: MIL-STD 1777, Reassembling state decision table (pg. 1-119).
The test "Where_to?" (pg. 1-126) tests the following to determine if the
datagram is "destined for this site":
1. Datagram options for completion of source route address visits,
2. Datagram destination address for identity with this host's id.
If either test fails, the decision table specifies that the HOST_UNREACH
parameter should be passed to the Error_to_Source routine (pg. 1-131).
PROBLEM 1: The Error_to_Source routine does not accept the HOST_UNREACH
parameter. Instead, it accepts the PROTOCOL_UNREACH parameter, which has
not been tested for by "Where_to?".
PROBLEM 2: Consulting RFC 792 (pg. 5) deepens the apparent inconsistency
by stating that the HOST_UNREACH parameter is generated by gateways, not hosts.
Additionally, D. P. Sidhu's execllent RFC 963 (pg. 16) reinforces the
PROTOCOL_UNREACH parameter by mentioning it in reference to another issue,
but does not cite it as a problem in itself.
QUESTIONS:
Is there really an inconsistency here, or have I missed something?
What information does the Internet Community expect the HOST_UNREACH ICMP
message to communicate?
Is it actually acceptable for a host to issue the HOST_UNREACH message
under the conditions described above?
Is there a discussion in the ICMP literature which would clarify the
usage of the HOST_UNREACH parameter, since it appears to be the correct
parameter to expect from a failed "Where_to?" test in a host environment.
Many thanks,
Linda Melvin
Senior programmer
infoPATH Communications Software Services, La Honda, CA
infopath@well.com.sf.ca.us
P.S. This is also my first attempt to use the TCP-IP forum.
Please advise if I've not done it correctly.stjohns@umd5.umd.edu (Mike St. Johns) (01/04/91)
Step 1: Throw away the mil-std. Step 2: Get a copy of RFC1122 The mil-std is hopelessly out of date - there was a concious decision by the PSSG (DCA's Protocol Standards Steering Group) not to update the standard as bugs were found. This was mainly due to wanting to emphasize the use of GOSIP. Mike