Specifications

ISSU Introduction
84 New and Enhanced Features in AlliedWare Plus 5.4.4 Major and Minor Versions
Introduction to ISSU
The In-Service Software Upgrade feature (ISSU) enables you to upgrade the software
running on the Controller Fabric Cards (CFCs) residing in either a standalone x8100 switch,
or stacked using x8100 VCStack Plus, while still forwarding data traffic.
Operating Requirements
ISSU is supported on the SwitchBlade x8100 Series chassis (or VCStack Plus). ISSU support
is subject to the following conditions:
■ Your Controller Fabric cards must be CFC960. CFC400 cards do not support ISSU.
■ Each chassis must contain two CFC960 cards to provide full ISSU functionality and
continuous network availability. You can however, still run the issu boot command
on page 94 with only one CFC card installed. This operation is subject to there being
a two chassis stack with at least one line card in each chassis, and there will be some
network down-time as each line card reboots. Note that in this scenario - unlike the
ISSU operation - all line cards and CFCs will reboot simultaneously causing a complete
network outage on the chassis during this period.
Key Concepts
The ISSU feature enables you to upgrade the software in each of the CFC960 controller
cards located within either a single chassis, or a stack of two x8100 chassis, while still
continuing to forward traffic. However, note that at the completion of ISSU’s automatic
phase, there will be a temporary mismatch between the software version running on the
controller cards, and that running on the Line Interface cards (LFIs). In order to complete
the ISSU process, the line cards must be rebooted to bring their software into line with
their CFCs.
Whether or not this process results in a network outage depends on the degree of
resiliency that is designed into the network itself. For example, in the network shown in
the section “VCStack Plus Resilient Stacked Topology Example” in the Software Reference,
VCStack Plus Introduction chapter, the CFC ISSU can be automatically accomplished, and
the manual line cards can be sequentially rebooted without halting the network traffic to
any of their remotely connected devices.
However, even in situations where the network has been designed for port density rather
than resiliency and does not use link aggregation to backup downstream devices, ISSU
still enables you to upgrade the CFCs to a later software version, and in addition allows
you time to schedule the line card reboots for a period of low network activity. Triggers
can also be employed to automatically schedule these reboots for an out of hours
operating period - see “Automating the ISSU Process Using Triggers” on page 90. Note
that all CFCs and line cards must be running the same software release before a
subsequent ISSU can be applied.
An important point to note is that in the ISSU processing order, the Active CFC is the last
controller card to be upgraded. For this reason when the Active CFC’s software is
upgraded, it hands over its “Active CFC” role to the card having the next highest priority. In
practice this will be the CFC in bay 1.5 to that in bay 1.6. Thus, applying an ISSU will result
in a semi permanent change of the card that is the stack’s Active CFC. This new CFC will
retain this role until the stack is next rebooted.