RSVP Diagnostic Messages
RFC 2745
Network Working Group A. Terzis
Request for Comments: 2745 UCLA
Category: Standards Track B. Braden
ISI
S. Vincent
Cisco Systems
L. Zhang
UCLA
January 2000
RSVP Diagnostic Messages
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
This document specifies the RSVP diagnostic facility, which allows a
user to collect information about the RSVP state along a path. This
specification describes the functionality, diagnostic message
formats, and processing rules.
1. Introduction
In the basic RSVP protocol [RSVP], error messages are the only means
for an end host to receive feedback regarding a failure in setting up
either path state or reservation state. An error message carries
back only the information from the failed point, without any
information about the state at other hops before or after the
failure. In the absence of failures, a host receives no feedback
regarding the details of a reservation that has been put in place,
such as whether, or where, or how, its own reservation request is
being merged with that of others. Such missing information can be
highly desirable for debugging purposes, or for network resource
management in general.
Terzis, et al. Standards Track [Page 1]
RFC 2745 RSVP Diagnostic Messages January 2000
This document specifies the RSVP diagnostic facility, which is
designed to fill this information gap. The diagnostic facility can
be used to collect and report RSVP state information along the path
from a receiver to a specific sender. It uses Diagnostic messages
that are independent of other RSVP control messages and produce no
side-effects; that is, they do not change any RSVP state at either
nodes or hosts. Similarly, they provide not an error report but
rather a collection of requested RSVP state information.
The RSVP diagnostic facility was designed with the following goals:
- To collect RSVP state information from every RSVP-capable hop
along a path defined by path state, either for an existing
reservation or before a reservation request is made. More
specifically, we want to be able to collect information about
flowspecs, refresh timer values, and reservation merging at each
hop along the path.
- To collect the IP hop count across each non-RSVP cloud.
- To avoid diagnostic packet implosion or explosion.
The following is specifically identified as a non-goal:
- Checking the resource availability along a path. Such
functionality may be useful for future reservation requests, but
it would require modifications to existing admission control
modules that is beyond the scope of RSVP.
2. Overview
The diagnostic facility introduces two new RSVP message types:
Diagnostic Request (DREQ) and Diagnostic Reply (DREP). A DREQ
message can be originated by a client in a "requester" host, which
may or may not be a participant of the RSVP session to be diagnosed.
A client in the requester host invokes the RSVP diagnostic facility
by generating a DREQ packet and sending it towards the LAST-HOP node,
which should be on the RSVP path to be diagnosed. This DREQ packet
specifies the RSVP session and a sender host for that session.
Starting from the LAST-HOP, the DREQ packet collects information
hop-by-hop as it is forwarded towards the sender (see Figure 1),
until it reaches the ending node. Specifically, each RSVP-capable
hop adds to the DREQ message a response (DIAG_RESPONSE) object
containing local RSVP state for the specified RSVP session.
Terzis, et al. Standards Track [Page 2]
RFC 2745 RSVP Diagnostic Messages January 2000
When the DREQ packet reaches the ending node, the message type is
changed to Diagnostic Reply (DREP) and the completed response is sent
to the original requester node. Partial responses may also be
returned before the DREQ packet reaches the ending node if an error
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