RSVP GR
RSVP graceful restart (GR) is a status recovery mechanism supported by RSVP-TE.
RSVP GR is designed based on non-stop forwarding (NSF). If a fault occurs on the control plane of a node, the upstream and downstream neighbor nodes send messages to restore RSVP soft states, but the forwarding plane does not detect the fault and is not affected. This helps stably and reliably transmit traffic.
RSVP GR uses the Hello extension to detect the neighboring nodes' GR status. For more information about the Hello feature, see RSVP Hello.
RSVP GR principles are as follows:
On the network shown in Figure 1, if the restarter performs GR, it stops sending Hello messages to its neighbors. If the GR-enabled helpers fail to receive three consecutive Hello messages, the helpers consider that the restarter is performing GR and retain all forwarding information. In addition, the interface board continues transmitting services and waits for the restarter to restore the GR status.
After the restarter restarts, if it receives Hello Path messages from helpers, it replies with Hello ACK messages. The types of the Hello messages returned by the upstream and downstream nodes on a tunnel are different:
If an upstream helper receives a Hello message, it sends a GR Path message downstream to the restarter.
If a downstream helper receives a Hello message, it sends a Recovery Path message upstream to the restarter.
If both the GR Path and Recovery Path messages are received, the restarter creates the new PSB associated with the CR-LSP. This restores information about the CR-LSP on the control plane.
If no Recovery Path message is sent and only a GR Path message is received, the restarter creates the new PSB associated with the CR-LSP based on the GR Path message. This restores information about the CR-LSP on the control plane.
The NetEngine 8000 F can only function as a GR Helper to help a neighbor node to complete RSVP GR.