So, your question is about is there a limit to the number of gateways you can register to CUCM? OR is your question more along the lines of is there a limit to the number of SRST-enabled users across the cumulative count of gateways in my environment?

For the first, I don’t know of a set limit of gateways. I have built CUCM clusters for school systems where every school has a single or even two gateways in addition to centralized gateways - so well over a 100 gateways configured without issue. If there is a hard limit, I am not aware of one.

As for the second, SRST maximum is not cumulative across devices. It is per device and is based on hardware, SRST version, and what you're licensed for. For example, a 3845 can support more SRST users than a 2801 but the 2 are independent of each other because once the devices are in SRST mode, they lose connection to CUCM (as you already know) and would have no direct IP / call setup path between them. They operate independently until the CUCM comes back online.

Hailey

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