Forum Discussion
pstavr
Cirrus
CirrusF5 Server SSL Profile using TLS 1.0 instead of TLS 1.2
Hi I have an F5 virtual server that does SSL inspection so it has a client ssl profile and a server ssl profile. The backend server is running on a Windows Server 2019 / IIS and it only accepts...
Hi all.
I found the root cause. The problem was related to the .NET app using SNI. By default the F5 doesn't do that.
https://devcentral.f5.com/s/articles/ssl-profiles-part-7-server-name-indication
So basically I just followed the fix in the above article, I defined a server name and the backend service started sending Server Hello etc. Everything works fine now!
Thank you all for your responses, as quite a few of them were helpful on identifying that the issue is with the app, and I could also spot a few things that were not proper on the negotiation part.
pstavr,
That is what I'm trying to explain.
The TLS1.0 Client Hello BIG-IP is sending is just a convention to signal which version it supports.
If your Windows client only sends TLS1.2/TLS1.2 it means it only supports TLS1.2 and nothing else.
Because BIG-IP supports TLS1.0, TLS1.1 and TLS1.2 it signals to server TLS1.0/TLS1.2.
This is expected behaviour.
And FYI, I took a capture on my Ubuntu box and this is my client hello:
Does it make sense?
Simon_Blakely
Employee
Employee> But if you restrict it to TLS 1.2, why would the F5 send TLS 1.0 as the lowest?
Late to the party, but you might appreciate this explanation:
F5 SSL profiles distinguish between Ciphers and Protocols.
Your cipher string restricts the cipher list to only those ciphers that are supported on TLSv1.2, but the server-ssl profile still supports the TLS Protocols from TLSv1 - TLSv1.2.
You can only negotiate TLSv1.2 ciphers on the TLSv1.2 Protocol, but you haven't explicitly instructed the profile to disable the earlier TLS Protocols, so it offers them.
You can disable TLS Protocols using the Options settings (No TLSv1, No TLSv1.1 ).
I hope this provides some useful information.