H3C Technologies H3C S12500-X Series Switches - Manual (Page 92)

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Path and Resv states to be refreshed. The Srefresh function reduces the number of refresh messages on the
network and speeds up refresh message processing.
Reliable RSVP message delivery
An RSVP sender cannot know or retransmit lost RSVP messages. The reliable RSVP message delivery
mechanism is designed to ensure reliable transmission.
This mechanism requires the peer device to acknowledge each RSVP message received from the local
device. If no acknowledgement is received, the local device retransmits the message.
To implement reliable RSVP message delivery, a node sends an RSVP message that includes a
Message_ID object in which the ACK_Desired flag is set. The receiver needs to confirm the delivery by
sending back a message that includes the Message_ID_ACK object. If the sender does not receive a
Message_ID_ACK within the retransmission interval (Rf), it retransmits the message when Rf expires and
sets the next transmission interval to (1 + delta) × Rf. The sender repeats this process until it receives the
Message_ID_ACK before the retransmission time expires or it has transmitted the message three times.
RSVP authentication
RSVP authentication ensures integrity of RSVP messages, and prevents false resource reservation requests
from occupying network resources.
With RSVP authentication, the sender uses the MD5 algorithm and the authentication key to calculate a
message digest for an RSVP message, and inserts the message digest to the RSVP message. When the
receiver receives the message, it performs the same calculation and compares the result with the message
digest. If they match, the receiver accepts the message. Otherwise, it drops the message.
By carrying a sequence number in a message, RSVP authentication can also prevent packet replay
attacks. The device records the sequence number of a received RSVP message, and determines whether
the subsequent messages are valid according to the recorded sequence number. If the sequence number
of a subsequent message is within the valid range, the device accepts the message. Otherwise, it drops
the message.
RSVP GR
RSVP GR preserves the soft state and label forwarding information when the signaling protocol or control
plane fails, so that LSRs can still forward packets according to forwarding entries.
RSVP GR defines the following roles:
• GR restarter—Router that gracefully restarts due to a manually configured command or a fault. It
must be GR-capable.
• GR helper—Neighbor of the GR restarter. A GR helper maintains the neighbor relationship with the
GR restarter and helps the GR restarter restore its LFIB information. A GR helper must be
GR-capable.
The device can act only as a GR helper.
The RSVP GR function depends on the extended hello capability of RSVP. A GR-capable device
advertises its GR capability and relevant time parameters to its neighbors in RSVP hello packets. If a
device and all its neighbors have the RSVP GR capability and have exchanged GR parameters, each of
them can function as the GR helper of another device.
A GR helper considers that a GR restarter is rebooting when it receives no hello packets from the restarter
in a specific period of time. When a GR restarter is rebooting, the GR helpers retain soft state information