We're configuring the allowlist on a SIP endpoint which will receive call traffic from Twilio. They provide CIDR blocks of the format .../30, which gives 4 addresses per region. However, per standard networking protocols, the first and last addresses are reserved for null/broadcast and not generally usable.
Are all 4 addresses per region valid sources? The documentation certainly indicates all 4 can send traffic. This appears to be an inconsistency with standard networking practices, or a misunderstanding on my part, so I wanted to clarify before we add them all.
Twilio Documentation: https://www.twilio.com/docs/sip-trunking/ip-addresses#north-america-virginia-gateways
Cheers!