This is the unique, non-meaningful index, ranging from 1 to 65535 and not necessarily contiguous, identifying one row in the Netasq firewall's active IPsec Security Association table. Because the value itself carries no semantic meaning, admins use it only to correlate the other columns, such as source and destination IP, SPI, encryption, and state, describing the same security association, not to infer anything about the SA's age or type. Two SAs with indexes 12 and 47 might be entirely unrelated tunnels to different peers; the gap doesn't imply missing entries.