Bgp Nonstop Routing Reference - Cisco NCS 5500 Series Configuration Manual

Information about Implementing BGP
To determine which address family to process, a next-hop notification is received by first de-referencing the
gateway context associated with the next hop, then looking into the gateway context to determine which
address families are using the gateway context. The IPv4 unicast and VPNv4 unicast address families share
the same gateway context, because they are registered with the IPv4 unicast table in the RIB. As a result, both
the global IPv4 unicast table and the VPNv4 table are is processed when an IPv4 unicast next-hop notification
is received from the RIB. A mask is maintained in the next hop, indicating if whether the next hop belongs
to IPv4 unicast or VPNv4 unicast, or both. This scoped table walk localizes the processing in the appropriate
address family table.
Reordered Address Family Processing
The software walks address family tables based on the numeric value of the address family. When a next-hop
notification batch is received, the order of address family processing is reordered to the following order:
• IPv4 tunnel
• VPNv4 unicast
• VPNv6 unicast
• IPv4 labeled unicast
• IPv4 unicast
• IPv4 MDT
• IPv6 unicast
• IPv6 labeled unicast
• IPv4 tunnel
• VPNv4 unicast
• IPv4 unicast
• IPv6 unicast
New Thread for Next-Hop Processing
The critical-event thread in the spkr process handles only next-hop, Bidirectional Forwarding Detection (BFD),
and fast-external-failover (FEF) notifications. This critical-event thread ensures that BGP convergence is not
adversely impacted by other events that may take a significant amount of time.
show, clear, and debug Commands
The show bgp nexthops command provides statistical information about next-hop notifications, the amount
of time spent in processing those notifications, and details about each next hop registered with the RIB. The
clear bgp nexthop performance-statistics command ensures that the cumulative statistics associated with
the processing part of the next-hop show command can be cleared to help in monitoring. The clear bgp
nexthop registration command performs an asynchronous registration of the next hop with the RIB.
The debug bgp nexthop command displays information on next-hop processing. The out keyword provides
debug information only about BGP registration of next hops with RIB. The in keyword displays debug
information about next-hop notifications received from RIB. The out keyword displays debug information
about next-hop notifications sent to the RIB.

BGP Nonstop Routing Reference

BGP NSR provides nonstop routing during the following events:
BGP Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.2.x
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Implementing BGP