ISSU Support between software Trains

[RICHARD MESSINGER]

Have customer that is very concerned with their core network being Non Stop even for software upgrades which have been problems in the past.

In researching different configurations with Chassis and dual sups the question of ISSU support comes up.

when doing ISSU, the support documents seem to indicate that it is supported when going from one release to another as long as we are within the same release train i.e. going from 17.2.3 to 17.4.2.

Is ISSU supported going between trains?  Can I expect an outage in a Dual Sup environment or in a dual Chassis VSS/VSP environment?

Thank you.

[Enes Simnica · Accepted solution]

hello @RICHARD MESSINGER ISSU helps minimize downtime during upgrades but is only supported within the same release train (17.2.x to 17.4.x). Cross-train upgrades ( 17.x to 18.x) are not supported and usually require a reload. So, in a Dual Sup setup, ISSU can be seamless if both sups support it and the upgrade path is compatible. Otherwise my Cisco friend, expect an outage LOool not funny tho..

and in dual chassis setups like VSS or StackWise Virtual, u can upgrade one chassis at a time. However, a brief switchover or traffic disruption may still occur, whichh means that nonstop operation isn't fully guaranteed, especially across release trains.

hope it helps and PEACE!

-Enes

[RICHARD MESSINGER]

Enes,  That is what I needed to confirm and is inline with what I expected to hear.  Always good to get a second opinion.

[Enes Simnica]

thank u Richard, and glad I could help confirm it. I really appreciate your insight and the experience you bring to the community!....

[O_A_H]

Hi Richard,

Adding some extra insights about this:

1- xfsu for 9300 switches upgrade. ISSU for 9400/9500/9600 switches upgrade.
2- xfsu/ISSU don't work for fabric switches in SD-Access environments (yet).
3- xfsu/ISSU don't work with cold SMUs.
4- xfsu/ISSU work within EM release or between EM releases.

[MHM Cisco World]

Thanks for additional info

Mr.Leo is king of upgrade of ios xe' he have a lot experience in upgrade.

Maybe he also can share his note

Thanks again 

MHM

[MHM Cisco World]

There are many limitations of ISSU in ios xe

If I have time I will update you with some doc.

Be careful 

MHM

[Leo Laohoo]

1.  xFSU is only for 9300X. 

2.  Regardless if this is a single- or dual supervisor card (per chassis), ISSU is not a one-shop-fits-all.  Some people had good experience with ISSU, however, I strongly recommend raising a proactive TAC case before embarking on an ISSU upgrade.  Reason for this madness is to ensure the ISSU upgrade is in "good hands" when things starts to deviate and the TAC agent, already on a WebEx call, can/will be able to immediate intervene.