Port 1645RADIUS Authentication (Cisco/Juniper)
Port 1645 was traditionally used for RADIUS authentication messages by vendors like Cisco and Juniper. As a protocol, RADIUS (Remote Authentication Dial In User Service) facilitates centralized Authentication, Authorization, and Accounting (AAA) for accessing network resources, widely adopted in network access servers, wireless controllers, VPNs, and more. Despite newer official port allocations, port 1645 remains in use in certain legacy or vendor-specific deployments..
- transport
- tcp · udp
- in transit
- cleartext
- assignment
- unofficial
- risk
- 4/10
- lookups
- 15,055
2 transports registered
payload readable on path
used by convention
caution
rank 218 of 993 · top 22%
Technical Details
what runs on :1645RADIUS (Remote Authentication Dial-In User Service) is a protocol designed to manage user authentication, authorization, and accounting, primarily in dial-up services but now used extensively across various network access scenarios like Wi-Fi, VPNs, and corporate networks. Port 1645 was historically used by Cisco and Juniper RADIUS authentication servers before IANA officially assigned ports 1812 (authentication) and 1813 (accounting).
RADIUS operates using a client-server model, where the NAS (Network Access Server) acts as a client and forwards user credentials to the RADIUS server for validation. Communication can occur over UDP and sometimes TCP, though UDP remains the primary transport. The packets include attribute-value pairs that facilitate user policy enforcement and session control.
While newer implementations favor the official ports, port 1645 is still in use because of legacy configurations and older equipment. The protocol supports multiple authentication methods, including PAP, CHAP, and EAP, and is designed for extensibility through vendor-specific attributes.
Security Information
exposure of :1645risk score
4/ 10caution
worth attention. how exposed you are depends on configuration — don't leave it reachable from the internet without a reason.
security averages 3.8 across 216 ports — this one sits 0.2 above.
in transit
cleartext
credentials and payloads are readable by anyone on path
assignment
unofficial
used by convention, not registered — what answers here varies by deployment
reachable over
tcp · udp
udp is connectionless — source addresses are trivially spoofed and it is a reflection favourite
security overview
Common Vulnerabilities:
- Use of outdated RADIUS over UDP without encryption exposes credentials to interception.
- Susceptibility to brute-force and dictionary attacks if weak passwords or authentication methods like PAP are used.
- IP spoofing to impersonate legitimate NAS clients.
- Replay attacks exploiting lack of message protection.
Mitigations:
- Deploy RADIUS over IPSec or within TLS tunnels like RadSec to provide encryption.
- Enforce strong password policies and multi-factor authentication.
- Restrict access to RADIUS servers via IP filtering and firewalls.
- Keep RADIUS software patched and disable legacy or insecure authentication schemes.
- Monitor logs for unusual authentication attempts to detect brute-force or spoofing attempts.
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risk mix of the 8 listed
- caution100%
3 of 8 encrypted