When disabling RC4 cipher globally on an F5 big IP LTM, will it cause any outage?

Hi Team,

  Just want clarification from F5 admins out there.  

We have a pair of Big IP LTM Model 3400 appliance in HA pair running version BIG-IP 10.2.4 Build 864.0 Hotfix HF11 .   We have many dozens of production VIPS and we just need to disable RC4 globally.  Luckily, all the SSL client profiles in all the VIPS have the default "clientssl"as their parent profile.

The "clientssl" profile has the current cipher list of DEFAULT:!SSLv3.     So looks like I have to add do not user RC4 so the cipher list now looks like  DEFAULT:!SSLv3:!RC4

Question: Once I do this,   do all the dependent SSL profiles automatically start "inheriting" this new cipher list from the parent clientssl?   i.e. No need to restart, disable/enable or anything like that?

Also,   what exactly happens once the !RC4 is added to the cipherlist?   Do all browsers connecting to the VIP start negotiating as normal, but not to try RC4?   Would there be any potential impacts to any old browsers?   Any outages I should be aware of?

There are many links on F5 describing cipher lists, but not specifically addressing what happens once the change kicks in.

Thanks and regards.
rleyba828Asked:
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David Johnson, CD, MVPOwnerCommented:
you should be using TLS vs SSL3.0.  SSL 3.0 has problems.. you should also be using elliptic curve encryption with perfect forward security.  https://www.digicert.com/ssl-support/ssl-enabling-perfect-forward-secrecy.htm
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arnoldCommented:
Test before the change using OpenSSL s_client -connect vip_ip:443 or if IMAPs/pop3s smtps .....there are .........

I think you are already excluding sslv3
See whether rc4 is currently available for the negotiation.


This will commonly mean tha rc4 will not be provided as a viable option to negotiate a connection.

My recomendation would be yo test first with one VIP create a new test profile with the rules ...

Very old export controlled browser might have an issue.

But unlikely.
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rleyba828Author Commented:
Hi Arnold,

   I tried your command above...and here is an extract of the output.  I can't put most of the extract here for security reasons, but I get this one  (I changed some bits in session id and Master key just for security)


New, TLSv1/SSLv3, Cipher is RC4-SHA
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
SSL-Session:
    Protocol  : TLSv1
    Cipher    : RC4-SHA
    Session-ID: B6214B3395AA9C374E15C55AF89E9D2E61D368811AAAAAA39AFDEA128D191526E3588
    Session-ID-ctx: 
    Master-Key: 4FAB6EE87BDE2108192ACA698186C3EF1D2931B1DBAAAAA1C7DDDB7D5C149B3A94463E72AC45CB110B5B9FC7DA17801
    Key-Arg   : None
    Start Time: 1440914132
    Timeout   : 300 (sec)
    Verify return code: 20 (unable to get local issuer certificate)

Open in new window


In the openssl command....how do I tell it to display the list of ciphers it is trying to use to negotiate?   In the example above,   I didn't put in the !RC4 option yet in the SSL profile as this is a production box.     I just wanted to see how the output looks like first.

* I notice that the cipher selected is RC4-sha

** Hi david,   we are already selecting TLS vs. SSLv3.
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arnoldCommented:
You have to look at the entire output from the beginning.

OpenSSL follows the /etc/OpenSSL.conf that is on your system or it can be where OpenSSL documents are.

The same way you have OpenSSL limited to which protocols/ciphers it will use.

openssl ciphers
 should list all authorized ciphers available to the open SSL client.

You should first work on disabling the cipher on the f5.

You can then limit the ciphers/.... On the client side.

In a windows environment, you would need to use ResEdit to find schannel to disable these ciphers.
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