[c-nsp] ISSU on SXF -> SXI

Rob Shakir rjs at eng.gxn.net
Fri Feb 12 09:47:58 EST 2010

On 12 Feb 2010, at 12:29, Phil Mayers wrote:

> * The old and new image are not ISSU-compatible (different major releases or feature sets) - in which case an RPR upgrade is the best you can do.
> * The old and new images are ISSU compatible, and the linecard software has not changed. In this case, the linecards do not need to be restarted, and downtimes of 0-3 seconds can be achieved because it's basically just an SSO switchover.
> * The old and new images are ISSU compatible but the linecard software is different, so the linecards need to be restarted into the new image - this can be a faster, warm boot (if the linecard has enough RAM) or a slower, cold boot (if not)
> I think that's about right?

This seems quite accurate to me.

Our experience of ISSU has been terrible. We've found multiple bugs related to it, and have found that -- in general -- we're much better off in terms of service disruption with a "classic" upgrade (upgrade secondary, reload peer, force failover, etc). 

Cisco advised us that it is unlikely that ISSU on 7600/6500 will meet our requirements, and hence we are better off doing classic upgrades. We've taken their advice, and will not be trying it again. I think it's suited for deployments where you have 30+ boxes that are identical in terms of configuration, and hardware, but in the SP environment (like us), the variance of boxes means that it's just not worthwhile.

Kind regards,

Rob Shakir                      <rjs at eng.gxn.net>
Network Development Engineer    GX Networks/Vialtus Solutions
ddi: +44208 587 6077            mob: +44797 155 4098
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