What port is used for RADIUS authentication?

Answer 1

RADIUS has been officially assigned UDP ports 1812 for RADIUS Authentication and 1813 for RADIUS Accounting by the internet Assigned Numbers Authority (IANA). However, prior to IANA allocation of ports 1812 and 1813, ports 1645 and 1646 (authentication and accounting, respectively) were used unofficially and became the default ports assigned by many RADIUS Client/Server implementations of the time. The tradition of using 1645 and 1646 for backwards compatibility continues to this day. For this reason many RADIUS Server implementations monitor both sets of UDP ports for RADIUS requests. Microsoft RADIUS servers default to 1812 and 1813 but Cisco devices default to the traditional 1645 and 1646 ports. Juniper Networks' RADIUS servers also default to 1645 and 1646.