Internet-Security raven logo internet-security.com

UDP 1646

ProtocolUDP
Port1646
LabelsOld radacct port RADIUS accounting protocol

Synopsis

  • UDP port 1646 is the legacy RADIUS Accounting port used by many networks for backward compatibility with early RADIUS implementations.
  • The original Livingston RADIUS server used 1646/UDP for accounting traffic.
  • FreeRADIUS can be configured to listen on 1646 for accounting (e.g., listen type=acct port=1646) and is commonly used this way in mixed/legacy environments.
  • Cisco networking gear (e.g., IOS/ASA) supports sending RADIUS accounting to servers on UDP/1646 via configurable acct-port settings.
  • Juniper’s Steel-Belted RADIUS (SBR) and Junos-based devices support using UDP/1646 for RADIUS accounting.
  • MikroTik RouterOS and HPE/Aruba switches/controllers allow configuring the RADIUS accounting port to 1646 to interoperate with legacy setups.
  • Security note: attackers often scan UDP/1646 (alongside 1813) for exposed RADIUS accounting services; misconfiguration can leak session metadata or be abused for DoS/reflection, so restrict source IPs and enforce strong shared secrets.

Observed activity

Last 30 days Detailed chart

More information