Bgp Graceful Restart; Cold Boot Caused By Power Cycling The System; Unexpected Reload Of The System; Software Upgrade - Dell S4048–ON Configuration Manual

BGP Graceful Restart

When the system contains one or more BGP peerings configured for BGP graceful restart, fast boot performs the following actions:
• A closure of the TCP sessions is performed on all sockets corresponding to BGP sessions on which Graceful Restart has been
negotiated. This behavior is to force the peer to perform the helper role so that any routes advertised by the restarting system are
retained and the peering session will not go down due to BGP Hold timeout.
• Termination of TCP connections is not initiated on BGP sessions without GR because such a closure might cause the peer to
immediately purge routes learnt from the restarting system.
• When BGP is started, it sets the R-bit and F-bit in the GR capability when bringing up the session with peers for which BGP GR has
been configured. This is the standard behavior of a restarting system and ensures that the peer continues to retain the routes
previously advertised by the system.
• The system delays sending the BGP End-of-RIB notification to peers with whom BGP GR has been negotiated to ensure that the local
routes of the system are advertised to the peers, if required by the configuration.
• If BGP GR is enabled on any peering session, the timeout values used for the BGP hold timer do not take effect.

Cold Boot Caused by Power Cycling the System

When you perform a power-cycle operation on a system that is configured with the optimized booting functionality, the system goes
through its regular boot sequence even if it is configured for fast boot. When the system comes up, it is expected that there will be no
dynamic ARP or ND database to restore. The system boot up mode will not be fast boot and

Unexpected Reload of the System

When an unexpected or unplanned reload occurs, such as a reset caused by the software, the system performs the regular boot sequence
even if it is configured for fast boot. When the system comes up, dynamic ARP or ND database entries are not present or required to be
restored. The system boot up mode will not be fast boot and actions specific to this mode will not be performed.

Software Upgrade

When fast boot is used to upgrade the system to a release that supports fast boot, the system enables the restoration of dynamic ARP or
ND databases that were maintained in the older release from when you performed the upgrade and the ARP and ND applications identify
that the system has been booted using fast boot.

LACP Fast Switchover

For fast boot, the operation of LACP has been optimized. These LACP optimizations are applicable even when fast boot is not enabled
when a system reload is performed. These enhancements are controlled using the fast-switchover option that is available with the lacp
command in Port Channel Interface Configuration mode. When LACP 'fast-switchover' is enabled on the system, two optimizations are
performed to the LACP behavior:
• The wait-while timer is not started in the 'waiting' state of the MUX state machine. The port moves directly to the 'attached' state.
• The local system moves to the 'collecting' and 'distributing' states on the port in a single step without waiting for the partner to set the
'collecting' bit.
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