Rsvp-Te State Refresh And Reliability - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - BGP AND MPLS CONFIGURATION GUIDE 2010-10-12 Configuration Manual

RSVP-TE State Refresh and Reliability

Copyright © 2010, Juniper Networks, Inc.
RSVP-TE messages carry objects consisting of type-length-values (TLVs). The label
request object instructs the endpoint LSR to return an resv message to establish the LSP.
The resv message contains the label object, the label used for the FEC. Both the path
and resv messages carry the record route object, which records the route traversed by
the message.
An upstream LSR sends a pathtear message when its path state times out as a result of
not being refreshed. The pathtear message removes the path and resv states in each
LSR as it proceeds downstream. Downstream LSRs similarly send the resvtear message
when their resv state times out to remove the resv states in upstream LSRs.
If a downstream LSR determines that it received an erroneous path message, it sends a
patherr message to the sender. If a reservation (label) request fails, the request initiator
sends a resverr message to the downstream LSRs. Both of these messages are advisory
and do not alter path or resv state.
RSVP-TE employs refresh messages to synchronize state between neighbors and to
recover from lost RSVP-TE messages of other types. RSVP-TE by default does not provide
for reliable transmission. Each node is responsible for the transmission of RSVP-TE
messages to its neighbors and relies on periodic state refreshes to recover from lost
messages.
RSVP-TE refresh reduction provides a means to increase reliability while reducing message
handling and synchronization overhead. Issuing the mpls rsvp refresh-reduction
command enables the following features:
The message ID object is included in RSVP-TE messages to provide a unique message
ID on a per-hop basis. In refresh messages, it indicates to the receiving node that the
message is a refresh message, eliminating the need for the node to completely analyze
the message and thus reducing the processing overhead at the receiver.
RSVP-TE uses a message acknowledgment mechanism to support reliable message
delivery on a per-hop basis. Messages that include the message ID object also include
a request for acknowledgment. Upon receipt, the receiving node returns a message
ack object, enabling the sending node to determine whether a message was lost and
triggering a retransmission as necessary.
Summary refresh (srefresh) messages refresh the state previously advertised in path
or resv messages that included message ID objects. The srefresh message carries the
unique message ID as state identifier, eliminating the need to send whole refresh
messages and reducing the overhead needed to maintain RSVP-TE state
synchronization. This method maintains RSVP-TE's ability to indicate when the state
is lost and to adjust to changes in routing. The srefresh message can carry message
IDs for multiple RSVP-TE sessions.
Issuing the mpls rsvp message-bundling command enables RSVP-TE to use bundle
messages, each of which includes multiple standard RSVP-TE messages, to reduce the
overall message processing overhead.
Chapter 3: MPLS Overview
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