Troubleshooting SSL handshake in F5 BIG-IP LTM – Part 1 (SSL/TLS Protocol Mismatch)

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” packetprotocol mismatch wireshark capture

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 --sslv2
curl -Ik --sslv3
curl -Ik --tlsv1
curl -Ik --tlsv1.0
curl -Ik --tlsv1.1
curl -Ik --tlsv1.2
  • Check if any protocol is negated in ciphers under client-ssl profile;

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Using curl for troubleshooting

View only response headers

curl -I only retrieves the header of the resource. The ‘I’ is case sensitive.

root@ubnsrv01:/etc/ssl/certs# curl -I
HTTP/1.1 200 OK
Content-Length: 191
Content-Type: text/html
Last-Modified: Thu, 17 Aug 2017 21:14:18 GMT
Accept-Ranges: bytes
ETag: "40d9a1c99d17d31:0"
Server: Microsoft-IIS/7.5
Date: Sat, 02 Sep 2017 22:58:54 GMT

View response headers and content

curl -i includes the HTTP header in the output along with the site content. Since this URL is terminating on an F5, the HTTP header reports that a redirect is configured for this URL but doesn’t redirect it automatically to the URL. The ‘i’ is case sensitive.

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