Users Guide

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.
Changes to BGP Multipath
When the system becomes active after a fast-boot restart, a change has been made to the BGP multipath and
ECMP behavior. The system delays the computation and installation of additional paths to a destination 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 manual intervention 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 conditions
One possible impact of this behavior change is that if the amount of traffic to a destination is higher than the
volume of traffic that can be carried over one path, a portion of that traffic might be dropped for a short
duration (30-60 seconds) after the system comes up.
Delayed Installation of ECMP Routes Into BGP
The current FIB component of Dell Networking OS has some inherent inefficiencies when handling a large
number of ECMP routes (i.e., routes with multiple equal-cost next hops). To circumvent this for the
configuration of fast boot, changes are made in BGP to delay the installation of ECMP routes. This is done
only if the system comes up through a fast boot reload. The BGP route selection algorithm only selects one
Flex Hash and Optimized Boot-Up 360