What are two factors to consider when implementing NSR High Availability on an MPLS PE router? (Choose two.)
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NSR (Nonstop Routing) is a feature that allows routing protocols to continue forwarding traffic during a control plane switchover, without dropping or interrupting the forwarding of packets. NSR High Availability is a mechanism that enables NSR across redundant routers in order to provide high availability for network services.
When implementing NSR High Availability on an MPLS PE (Provider Edge) router, there are several factors that need to be considered, including:
Compatibility with PE-CE sessions: NSR High Availability requires all PE-CE (Customer Edge) sessions to support NSR. If a CE device does not support NSR, the router will fall back to NSF (Nonstop Forwarding), which provides packet forwarding continuity, but not control plane continuity. Therefore, it is important to verify that all CE devices support NSR before implementing NSR High Availability.
Routing protocol extensions: In order to support NSR High Availability, routing protocols such as OSPF, IS-IS, and BGP require specific extensions to their protocols. For example, BGP requires the "BGP graceful restart" capability, which enables a BGP speaker to maintain its BGP session with a peer during a control plane switchover. OSPF and IS-IS require "graceful restart" extensions, which allow a router to maintain its adjacencies during a control plane switchover. Therefore, it is important to ensure that the routing protocols in use support the required extensions for NSR High Availability.
Memory and CPU resources: NSR High Availability consumes more memory and CPU resources than NSF, as it requires the router to maintain a backup control plane instance. Therefore, it is important to ensure that the router has sufficient resources to support NSR High Availability.
Operation without NSR support: NSR High Availability operates normally without NSR support on the PE peers. However, if a PE peer does not support NSR, the router will fall back to NSF. Therefore, it is important to ensure that all PE peers support NSR in order to fully benefit from NSR High Availability.
State information synchronization: NSR High Availability allows state information to be synchronized across redundant routers, which helps to ensure consistent network operation. However, it cannot sync state information across redundant RPs (Routing Processors). Therefore, it is important to ensure that the routers are configured to use the same RP for the control plane switchover.