Information Technology Reference
In-Depth Information
End-of-RIB Marker
The end-of-RIB marker indicates to a BGP peer that the initial routing update has completed
after session initiation. This feature is valuable for BGP convergence independently of
BGP-GR. For general convergence, the end-of-RIB marker can serve as a trigger for BGP
to run the best-path algorithm. This allows BGP to remain in read-only mode until the end-
of-RIB marker is received for all peers. The best-path algorithm creates the local RIB. The
BGP updates are built, efficiently packed, and sent to the remote peers.
For IPv4, the end-of-RIB marker is a BGP Update message with no reachable NLRI and
empty withdrawn NLRI. Additional address families indicate the end-of-RIB with a BGP
Update containing only the MP_UNREACH_NLRI attribute with no withdrawn routes for
that AFI/SAFI. Although Cisco IOS does not send a keepalive until after the initial routing
update, not all vendors conform to this behavior. The end-of-RIB provides an interoperable
method of indicating the end of the initial routing update. This functionality is independent
of BGP-GR can be used even when BGP-GR is not being used.
Graceful Restart Capability
The graceful restart capability, shown in Figure 3-5, is sent one time, as part of the capabil-
ities negotiation process discussed in Chapter 2, in the section “BGP Capabilities.” The
graceful restart capability carries several important pieces of information. The existence of
this capability indicates that the peer intends to use the end-of-RIB marker. This capability
also contains the Restart State, Restart Time in the Restart Flags, and Forwarding State for
each AFI/SAFI, as part of the Address Family flags.
Figure 3-5
BGP Graceful Restart Capability
Restart Flags (4 Bits)
Restart Time in Seconds (12 Bits)
Address Family Identifier (16 Bits)
Subsequent Address Family Identifier (8 Bits)
Flags for Address Family (8 Bits)
...
Address Family Identifier (16 Bits)
Subsequent Address Family Identifier (8 Bits)
Flags for Address Family (8 Bits)
