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I'm trying to debug an LDAPS connection from Ubuntu 14.04 to some sort of VIP. There are 6 nodes behind the VIP. The connection only succeeds "sometimes". A wireshark log shows the failing connections being issued TLSv1.2 Alerts "Fatal, Illegal Parameter" with a Content Type "Alert (21)" which apparently only means wireshark can't decrypt the alert record. enter image description here

I don't have access to the server's private key so I cannot decrypt the wireshark session. I'm trying to get the server admin to do it. In the meantime, is there any way to find out what cipher is being settled on with the connection does work? I've tried ldapsearch -d 255 ... but it doesn't reveal anything about the cipher that I can see, so far.

When the connection does succeed, The TLS record layer in wireshark says looks like this, if it's of any use: enter image description here

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I think you need to use OpenSSL to connect to the server and see what ciphers are returned.

Try

openssl s_client -connect ldapserver.domain:636

It should return a line for "Ciphers"

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  • Looks like: Protocol : TLSv1.2 Cipher : AES256-SHA. So, the server only supports that cipher? Maybe I should mention ldapsearch is compiled against gnutls on my system and not openssl if that matters. Oct 9, 2018 at 20:53

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