What is the impact of a nondisruptive upgrade on fabric and modular switches?

While the control plane is disrupted, stating 'more than 120 seconds' is generally an overestimation for the control plane convergence time during a nondisruptive ISSU, which is typically shorter.

During a nondisruptive upgrade (ISSU) on fabric and modular switches, although the data plane generally remains operational, the control plane experiences a temporary disruption during the supervisor module switchover. This temporary state can prevent new devices from establishing logins or sessions with the fabric until the upgrade is complete and the control plane fully stabilizes.

Performing an upgrade during a zone server merge is highly disruptive and not supported; the upgrade would either fail or halt rather than continuing without interruption.

System BIOS updates are usually separate procedures and not an automatic or inherent part of every nondisruptive software upgrade for fabric or modular switches.