3.
The GR session between the GR Restarter and its peer goes down when the GR Restarter restarts BGP. The
GR capable peer will mark all routes associated with the GR Restarter as stale. However, during the
configured GR Time, it still uses these routes for packet forwarding.
4.
After the restart, the GR Restarter will reestablish a GR session with its peer and send a new GR message
notifying the completion of restart. Routing information is exchanged between them for the GR Restarter to
create a new routing table and forwarding table with stale routing information removed. Then the BGP routing
convergence is complete.
Route refresh
When the inbound policy-filter for a peer changes, the routes advertised by the peer must be presented to the
policy-filter engine to take effect. This means that all the routes that were received from a peer will have to be
preserved in the router and this would raise the demand on memory and CPU resources of the router. The route
refresh capability allows the router to request the peer to re-advertise the routes thereby avoiding the requirement
to keep a copy of all the routes that were received from all the peers.
BGP basic configuration
The following configuration tasks are described as required or optional.
Task
Remarks
Configuring BGP connection
Required
Controlling route distribution and
reception
Configuring BGP route redistribution Optional
Configuring BGP route distribution
filtering policies
Optional
Configuring BGP route reception
filtering policies
Optional
Routemap filtering and route
modifications
Optional
Configuring BGP route attributes
Optional
Tuning and optimizing BGP
networks
Optional
Configuring BGP community
Optional
Configuring BGP GR
Optional
Configuring a BGP connection
NOTE:
Since BGP runs on TCP, you must specify the IP addresses of the peers in order to establish a BGP
session. The peers may not be directly connected.
IP addresses of loopback interfaces can be used to improve the stability of BGP connections.
Prerequisites
The neighboring nodes must be accessible to each other at the network layer.
Chapter 17 Border Gateway Protocol (BGP)
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