How to identify if there is an SSL/TLS protocol mismatch between Client and F5 LTM?

1.  Check the protocol version used by the client in wireshark captures under the “Client Hello” packet

2.  Check the SSL/TLS protocol version supported by the LTM for a particular VIP

• Run curl checks if possible from a remote server

curl -Ik https://site1.dc1.networkology.net --sslv2
curl -Ik https://site1.dc1.networkology.net --sslv3
curl -Ik https://site1.dc1.networkology.net --tlsv1
curl -Ik https://site1.dc1.networkology.net --tlsv1.0
curl -Ik https://site1.dc1.networkology.net --tlsv1.1
curl -Ik https://site1.dc1.networkology.net --tlsv1.2

• Check if any protocol is negated in ciphers under client-ssl profile;

tmsh list ltm virtual <VIRTUAL-SERVER> { profiles }
tmsh list ltm profile client-ssl <PROFILE-NAME> { ciphers }

    ltm profile client-ssl site1.dc1.networkology.net-clientssl {
        ciphers !TLSv1:DEFAULT
    }

• Check if the protocol is negated in options list under client-ssl profile;

tmsh list ltm profile client-ssl <PROFILE-NAME> { options }
ltm profile client-ssl site1.dc1.networkology.net-clientssl {
        options { no-tlsv1 }
    }

• Check if the DEFAULT cipher string does not have the required protocol in the list;

tmm --clientciphers DEFAULT | grep "TLS1.1"
tmm --clientciphers DEFAULT | grep "TLS1"
tmm --clientciphers DEFAULT | grep "TLS1.2"

Supplementary information:

List of cipher suites supported under 11.x to 13.x version – https://support.f5.com/csp/article/K13163

List of cipher/protocols under the DEFAULT cipher string for version 11.x and 12.x – https://support.f5.com/csp/article/K13171

The <cipher string> can be any of the standard cipher string identifiers, such as ALL, DEFAULT, LOW, MEDIUM, HIGH, and NULL.