/etc/services
(or equivalent on your system).
Multiple comma-separated ports may be specified. The default port is 1646.
Note that the officially assigned port number for RADIUS accounting has
been changed to 1813. AcctPort may contain special formatting characters.
A typical use of special formatting characters is with GlobalVar and
command line arguments.# Listen for accounting requests on port 1813 as # per RFC 2866 AcctPort 1813
# Do not bind to an accounting port: AcctPort
AcctPort 1646,1813