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 RSVP 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 about the GR restarter and continue sending hello packets periodically to the GR restarter until the restart timer expires.
If a GR helper receives a hello message from the GR restarter before the restart timer expires, the recovery timer is started and signaling packet exchange is triggered to restore the original soft state. Otherwise, all RSVP soft state information and forwarding entries relevant to the neighbor are removed. When the recovery timer expires, soft state information and forwarding entries that are not restored are removed.