Port 3128 supports HTTP proxy and ndl-aas (UDP reference coverage) across distinct transports. Review each protocol before writing firewall or monitoring policy.
Common listener for Squid and other HTTP forward proxies.
HTTP proxy endpoints in environments where this service is explicitly configured.
Client to server
Prevent open-proxy access, authenticate clients, restrict CONNECT destinations, and log egress appropriately.
ndl-aas (UDP reference coverage) is documented as a network service convention for port 3128 over UDP.
Use this reference entry when identifying or validating systems documented to use 3128/UDP.
Varies
Confirm the listening process and current vendor documentation before permitting traffic; a listed convention does not prove the active service or its security posture.