Service Manual

A le is generated to indicate that the system is undergoing a fast boot, which is used after the system comes up.
After the Dell Networking OS image is loaded and activated, and the appropriate software components come up, the following
additional actions are performed:
• If a database of dynamic ARP entries is present on the ash drive, that information is read and the ARP entries are restored; the
entries are installed on the switch as soon as possible. At the same time, the entries are changed to an initial (“aged out”) state
so that they are refreshed (and ushed if not learnt again). The database on the ash card is also deleted instantaneously.
• The system ensures that local routes known to BGP are imported into BGP and advertised to peers as quickly as possible. In this
process, any advertisement-interval conguration is not considered (only during the initial period when the peer comes up).
If you do not congure BGP GR, you must congure the peering with BGP keepalive and hold timers to be as high as possible
(depending on your network deployment and the scaled parameters or sessions) to enable the connection to be active until the
system re-initializes the switch, causing the links to adjacent devices to go down. If the BGP sessions are disabled before the re-
initialization of the switch occurs because of the peer timing out, trac disruption occurs from that point onwards, even if the
system continues to maintain valid routing information in the hardware and is capable of forwarding trac.
LACP and IPv6 Routing
The following IPv6-related actions are performed during the reload phase:
• The system saves all the dynamic ND cache entries to a database on the ash card. After the system comes back online, and the
Dell Networking OS image is loaded and the corresponding software applications on the system are also activated, the following
processes specic to IPv6 are performed:
• If a database of dynamic ND entries is present on the ash, the information is read and the ND entries are restored (to the IPv6
subsystem as well as the kernel); the entries are installed on the switch as quickly as possible. At the same time, the entries are
changed to an initial (“incomplete”) state so that they are refreshed (and ushed, if not learnt again). The database on the ash
is also deleted immediately.
• To ensure that the adjacent systems do not time out and purge their ND cache entries, the age-out time or the reachable time
for ND cache entries must be congured to be as high as necessary. Dell recommends that you congure the reachable timer to
be 90 seconds or longer.
BGP Graceful Restart
When the system contains one or more BGP peerings congured 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 congured. 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 notication 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 conguration.
• If BGP GR is enabled on any peering session, the timeout values used for the BGP hold timer do not take eect.
Cold Boot Caused by Power Cycling the System
When you perform a power-cycle operation on a system that is congured with the optimized booting functionality, the system goes
through its regular boot sequence even if it is congured 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
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Flex Hash and Optimized Boot-Up