Which remote access VPN technology requires transform sets to be explicitly defined?

Clientless SSL VPN relies on TLS for transport security and uses SSL cipher suites negotiated automatically by the protocol itself, not Cisco IOS IPsec transform sets.

IPsec VPN on Cisco IOS uses the 'crypto ipsec transform-set' command to explicitly declare the combination of encryption algorithms (such as AES or 3DES) and integrity algorithms (such as SHA or MD5). Without a defined transform set referenced in a crypto map or IPsec profile, the IPsec SA cannot be negotiated and the tunnel cannot be established.

Cisco AnyConnect in SSL mode uses TLS and requires no transform sets; when AnyConnect operates over IKEv2, the configuration uses IKEv2 proposals rather than legacy IKEv1-style transform sets.

FlexVPN is an IKEv2-based framework that uses 'crypto ikev2 proposal' and 'crypto ikev2 policy' constructs in place of the explicit transform set definition required by IKEv1 IPsec.