Port 1701 supports L2TP and l2f (TCP reference coverage) across distinct transports. Review each protocol before writing firewall or monitoring policy.
Carries Layer 2 Tunnelling Protocol control and data traffic.
L2TP/IPsec remote-access and site-to-site VPNs.
Bidirectional
L2TP alone provides no encryption; pair with correctly configured IPsec and avoid weak authentication.
l2f (TCP reference coverage) is documented as a network service convention for port 1701 over TCP.
Use this reference entry when identifying or validating systems documented to use 1701/TCP.
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.