Symptoms

SSL performs cipher selection and ALPN protocol selection independently. It is possible that SSL picks a cipher that is not compatible with HTTP/2. This causes an issue where either the client or the BIGIP will refuse a newly established HTTP/2 connection with error INSUFFICIENT_SECURITY.

Impact

Client or the BIG-IP system refuses a newly established HTTP/2 connection with error INSUFFICIENT_SECURITY.

Conditions

SSL picks a cipher that is not compatible with HTTP/2, but picks HTTP/2 (h2) as the next protocol.

Workaround

Make sure HTTP/2 ciphers always come before non HTTP/2 ciphers. This is not the case with the DEFAULT cipher string. HTTP/2 requires TLS 1.2 (or above) Ephemeral keys (EDH/RSA, ECDHE_ECDSA, ECDHE_RSA, DHE/DSS) GCM (AES-GCM).

Fix Information

In this release, HTTP/2 ciphers always come before non HTTP/2 ciphers, at the top of the list, so they always in sync and do not result in connection errors.

Behavior Change