At the writing of this article there are 2 methods to upgrade releases or install SMUs on XR
1) This is a standard "Install add/activate" method which does not exercise the ISSU function
In this step software is downloaded from tftp/ftp server to the router and activating
the software thereafter. This method will reload the router during a software upgrade.
In summary from any release to any release using this method will
incur a reload. This method is supported on all releases for all installation operations.
SMU install operation using this method will depend on the type of SMU that is being installed.
If the SMU is marked "Hitless or dependent" or "Traffic loss or dependent" in Cisco Software Manager (CSM),
or in the SMU readme then the install activation will not reload the box, check the readme or DDTS
for more details on the impact to traffic and the period.
If the SMU is marked "reboot" or "ISSU/Reload", in Cisco Software Manager (CSM), or in the SMU readme,
the SMU activation will result in a complete system reboot. Even if the SMU is marked ISSU.
See this chapter for install operation instructions.
http://www.cisco.com/en/US/docs/routers/asr9000/software/asr9k_r4.3/system_management/configuration/guide/b_sysman_cg43asr9k_chapter_0100.html
This link has per release upgrade instructions, as well as per release recommended SMU list.
http://www.cisco.com/web/Cisco_IOS_XR_Software/index.html
For more information about Cisco Software Manager (CSM) AKA SMU manager reference the CSM user guide:
http://www.cisco.com/en/US/docs/routers/asr9000/software/smu/csmuser.html
The tool is now available to be downloaded from the IOS XR software download section on Cisco.com
2) ISSU operations; ISSU is supported under the following context
A) Installing an ISSU SMU that is marked as ISSU in CSM or the DDTS.
B) Upgrading from one release to another release using ISSU, an example of this is 4.3.0 to 4.3.1
Before performing any ISSU SMU installation it's first important to check that the software being used
is ISSU compatible, for a SMU check in CSM or SMU readme for "ISSU" keyword next to the "Impact" field.
For standard release upgrades check the release notes and upgrade instructions for ISSU compatibility or support,
check also for caveats.
As an example an upgrade from 4.3.0 to 4.3.1 is possible through ISSU method, the first requirement
is to have C-SMU2 for 4.3.0 active on the system (install via the "Install add/activate" method) before an ISSU upgrade
to 4.3.1 is performed. At the writting of artical ISSU support is only available for upgrades from 4.3.0 to 4.3.1, and it
is available for ISSU SMUs starting from 4.2.1.
ISSU installation example:
http://www.cisco.com/en/US/docs/routers/asr9000/software/asr9k_r4.3/system_management/configuration/guide/b_sysman_cg43asr9k_chapter_0100.html#reference_B7C5F51711C446FDAACF4A04930AA01A
3) Upgrading a system with NV EDGE technology enabled.
There are two methods available to upgrade an NV-EDGE(Cluster) system.
A) The standard install add/activate method which will upgrade the system just like any single chassis.
Using this process the software is distributed to both chassis in the cluster, and the software is then
activated just like a single chassis, this is just like section 1 above (standard install add/activate), and
holds for SMU installation and software upgrades. No special instructions are needed, ie Racks do not need
to be shutdown or isolated. It's highly recommended that the same steps used on a single chassis are also
used here.
B) Scripted upgrade for NV EDGE
Install add/activate method using the scripted upgrade reduces downtime by upgrading one rack at
a time, while isolating the other rack to avoid both racks running different software. This method is recommended
for upgrades on NV EDGE systems that desire the least downtime, but external servers to run the
script, as well as console access is needed. Details steps and location of the script can be found in
section 13 in the NV EDGE deployment guide:
NV EDGE deployment guide:
https://supportforums.cisco.com/docs/DOC-34114
ISSU UPGRADES on NV EDGE ARE NOT SUPPORTED
4) Upgrading an NV Satalite system
There is one method to upgrade an NV Satalite system this method is well documented on Cisco.com reference section:
"Upgrading and Managing Satellite nV Software"
http://www.cisco.com/en/US/docs/routers/asr9000/software/asr9k_r4.2/interfaces/configuration/guide/hc42satl.pdf
