This is the table index (1 through 8) that identifies a specific TACACS+ server entry within the per-server authentication statistics table, letting the switch and any management system correlate a given row's counters back to one particular configured authentication server rather than the device-wide totals. An admin troubleshooting 'some logins are slow, some aren't' would use this index to pull the counters for server 3 specifically instead of relying on the Global counters, which blend all servers together. For example, if a switch has three TACACS+ servers configured for authentication, this object distinguishes rows 1, 2, and 3 so their individual timeout and reject counts can be compared side by side.