dynamic ARP or ND database entries are not present or required to be restored. The system boot upmode will not be fast boot and actions specific to this mode will not be performed.Software UpgradeWhen fast boot is used to upgrade the system to a release that supports fast boot, the system enables therestoration of dynamic ARP or ND databases that were maintained in the older release from when youperformed the upgrade and the ARP and ND applications identify that the system has been booted usingfast boot.LACP Fast SwitchoverFor fast boot, the operation of LACP has been optimized. These LACP optimizations are applicable evenwhen fast boot is not enabled when a system reload is performed. These enhancements are controlledusing the fast-switchover option that is available with the lacp command in Port Channel InterfaceConfiguration mode. When LACP ‘fast-switchover’ is enabled on the system, two optimizations areperformed to the LACP behavior:• The wait-while timer is not started in the ‘waiting’ state of the MUX state machine. The port movesdirectly to the ‘attached’ state.• The local system moves to the ‘collecting’ and ‘distributing’ states on the port in a single step withoutwaiting for the partner to set the ‘collecting’ bit.Changes to BGP MultipathWhen the system becomes active after a fast-boot restart, a change has been made to the BGP multipathand ECMP behavior. The system delays the computation and installation of additional paths to adestination into the BGP routing information base (RIB) and forwarding table for a certain period of time.Additional paths, if any, are automatically computed and installed without the need for any manualintervention in any of the following conditions:• After 30 seconds of the system returning online after a restart• After all established peers have synchronized with the restarting system• A combination of the previous two conditionsOne possible impact of this behavior change is that if the amount of traffic to a destination is higher thanthe volume of traffic that can be carried over one path, a portion of that traffic might be dropped for ashort duration (30-60 seconds) after the system comes up.Delayed Installation of ECMP Routes Into BGPThe current FIB component of Dell Networking OS has some inherent inefficiencies when handling alarge number of ECMP routes (i.e., routes with multiple equal-cost next hops). To circumvent this for theconfiguration of fast boot, changes are made in BGP to delay the installation of ECMP routes. This is doneonly if the system comes up through a fast boot reload. The BGP route selection algorithm only selectsone best path to each destination and delays installation of additional ECMP paths until a minimum of 30seconds has elapsed from the time the first BGP peer is established. Once this time has elapsed, all routesin the BGP RIB are processed for additional paths.334 Flex Hash and Optimized Boot-Up
