RFC 2745 (rfc2745) - Page 3 of 23
RSVP Diagnostic Messages
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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
condition along the path, such as "no path state", prevents further
forwarding of the DREQ packet. To avoid packet implosion or
explosion, all diagnostic packets are forwarded via unicast only.
Thus, there are generally three nodes (hosts and/or routers) involved
in performing the diagnostic function: the requester node, the
starting node, and the ending node, as shown in Figure 1. It is
possible that the client invoking the diagnosis function may reside
directly on the starting node, in which case that the first two nodes
are the same. The starting node is named "LAST-HOP", meaning the
last-hop of the path segment to be diagnosed. The LAST-HOP node can
be either a receiver node or an intermediate node along the path.
The ending node is usually the specified sender host. However, the
client can limit the length of the path segment to be diagnosed by
specifying a hop-count limit in the DREQ message.
LAST-HOP Ending
Receiver node node Sender
__ __ __ __ __
| |---------| |------>| |--> ...-->| |--> ...---->| |
|__| |__| DREQ |__| DREQ |__| DREQ |__|
^ . |
| . |
| DREQ . DREP | DREP
| . |
_|_ DREP V V
Requester | |