BGP GR and NSR
BGP graceful restart (GR) and non-stop routing (NSR) are high availability solutions that minimize the impact of device failures on user services.
BGP GR
BGP GR ensures that the forwarding plane continues to guide data forwarding during a device restart or active/standby switchover. The operations on the control plane, such as reestablishing peer relationships and performing route calculation, do not affect the forwarding plane. This mechanism prevents service interruptions caused by route flapping and improves network reliability.
GR concepts are as follows:
GR restarter: is the device that is restarted by the administrator or triggered by failures to perform GR.
GR helper: is the neighbor that helps the GR restarter to perform GR.
GR time: is the time during which the GR helper retains forwarding information after detecting the restart or active/standby switchover of the GR restarter.
Using the BGP capability negotiation mechanism, the GR restarter and helper know each other's GR capability and establish a GR session.
When detecting the restart or active/standby switchover of the GR restarter, the GR helper does not delete the routing information and forwarding entries of the GR restarter or notify other neighbors of the restart or switchover, but waits to reestablish a BGP connection with the GR restarter.
The GR restarter reestablishes neighbor relationships with all GR helpers before the GR time expires.
BGP NSR
NSR is a reliability technique that prevents neighbors from detecting the control plane switchover. It applies to the devices that have the active and standby MPUs configured. Compared to GR, NSR does not require the help of neighbors and does not need to deal with interoperability issues. For details about NSR, see "NSR" in the Configuration Guide - Reliability - Introduction to Reliability.
NSR is enabled on the device by default and does not need to be configured.
Comparisons Between Active/Standby Switchovers with and Without GR and NSR
Active/Standby Switchover Without GR and NSR |
Active/Standby Switchover in GR Mode |
Active/Standby Switchover in NSR Mode |
|---|---|---|
The BGP peer relationship is reestablished. |
The BGP peer relationship is reestablished. |
The BGP peer relationship is reestablished. |
Routes are recalculated. |
Routes are recalculated. |
Routes are recalculated. |
The forwarding table changes. |
The forwarding table remains unchanged. |
The forwarding table remains unchanged. |
Traffic is lost during forwarding, and services are interrupted. |
No traffic is lost during forwarding, and services are not affected. |
No traffic is lost during forwarding, and services are not affected. |
The network detects route changes, and route flapping occurs for a short period of time. |
Except the neighbors of the device where the active/standby switchover occurs, other routers do not detect route changes. |
The network does not detect route changes. |
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The GR restarter requires neighbors to support the GR helper function. The GR helper function does not allow multiple neighbors to perform active/standby switchovers in GR mode simultaneously. |
Neighbors do not need to support the NSR function. |