UDP Port 500 – ISAKMP / IKE (IPsec Key Exchange)

About UDP Port 500

Port 500 carries the IANA assignment for isakmp. The IANA description reads: ‘isakmp’. This port appears in 23 IDS rules and does not have notable malware activity indicators in our data.

IDS Rule References

23 IDS / security rules reference UDP port 500. Treat that number as context, not a danger score. Many detection rules are written against groups of ports rather than one service, web ports especially, so common web alternate ports inherit large counts while genuinely sensitive services can show few rules or none. Presence in IDS rules does not mean traffic on this port is malicious.

Rule categories (top 6): attempted-admin (6), trojan-activity (3), misc-attack (3), attempted-recon (3), misc-activity (2), attempted-user (2).

Sample rule descriptions for UDP port 500:

• POLICY-OTHER IPSec PGPNet connection attempt
• INDICATOR-SCAN isakmp login failed
• SERVER-OTHER ISAKMP first payload certificate request length overflow attempt
• SERVER-OTHER ISAKMP second payload certificate request length overflow attempt
• SERVER-OTHER ISAKMP third payload certificate request length overflow attempt

Data Sources

This information is compiled from: IANA Service Name and Transport Protocol Port Number Registry, Emerging Threats Open Ruleset (BSD 2-Clause / GPLv2 per SID range), and Snort Community Rules (GPLv2).