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Netscaler vs Exchange 2019 "time out during ssl handshake stage

If you are using Citrix Netscaler as load balancer in front of Exchange 2019 server you must know this:

Microsoft Exchange 2019 is secured by default and allows only TLS 1.2. Therefore default schannel settings are as follows (using IISCrypto tool from Nartac Software):



While Citrix Netscaler offers following Cipher Suites:

TLS_RSA_WITH_AES_256_CBC_SHA
TLS_RSA_WITH_AES_128_CBC_SHA
TLS_DHE_RSA_WITH_AES_256_CBC_SHA
TLS_DHE_RSA_WITH_AES_128_CBC_SHA
TLS_DHE_DSS_WITH_AES_256_CBC_SHA
TLS_DHE_DSS_WITH_AES_128_CBC_SHA
TLS_RSA_WITH_DES_CBC_SHA
TLS_RSA_EXPORT_WITH_DES40_CBC_SHA
TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5
TLS_DHE_DSS_WITH_DES_CBC_SHA
TLS_DHE_DSS_EXPORT1024_WITH_DES_CBC_SHA
TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA
TLS_DHE_RSA_WITH_DES_CBC_SHA
TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA
TLS_RSA_EXPORT1024_WITH_RC2_CBC_56_MD5
TLS_DH_anon_WITH_DES_CBC_SHA
TLS_DH_anon_WITH_AES_128_CBC_SHA
TLS_DH_anon_WITH_AES_256_CBC_SHA
TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA

Now, you will find that you also need to change following registry keys to 1 to downgrade security on your Exchange server (read more)

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL]
"AllowInsecureRenegoClients"=dword:00000001
"AllowInsecureRenegoServers"=dword:00000001

But if you do just that Citrix Netscaler will still not work with your Exchange 2019 server. You need to enable TLS 1.1 and the Cipher Suites that accompany TLS 1.1




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Comments

  1. RalphOctober 6, 2020 at 11:05 PM

    This absolutely saved me, thank you so much. Excellent info!

    ReplyDelete

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