the iRule below can be used to inject a TLS SNI extension to the server side based on e.g. HOST-Header values. The iRule is usefull if your pool servers depending on valid SNI records and you don’t want to configure dedicated Server SSL Profiles for each single web application.
Cheers, Kai
How to use this snippet:
Attach the iRule to the Virtual Server where you need to insert a TLS SNI expension
Tweak the
$sni_value
variable within the
HTTP_REQUEST
to meet your requirements or move it to a different event as needed.
Make sure you’ve cleared the “Server Name” option in your Server_SSL_Profile.
Code :
when HTTP_REQUEST {
#Set the SNI value (e.g. HTTP::host)
set sni_value [getfield [HTTP::host] ":" 1]
}
when SERVERSSL_CLIENTHELLO_SEND {
# SNI extension record as defined in RFC 3546/3.1
#
# - TLS Extension Type = int16( 0 = SNI )
# - TLS Extension Length = int16( $sni_length + 5 byte )
# - SNI Record Length = int16( $sni_length + 3 byte)
# - SNI Record Type = int8( 0 = HOST )
# - SNI Record Value Length = int16( $sni_length )
# - SNI Record Value = str( $sni_value )
#
# Calculate the length of the SNI value, Compute the SNI Record / TLS extension fields and add the result to the SERVERSSL_CLIENTHELLO
SSL::extensions insert [binary format SSScSa* 0 [expr { [set sni_length [string length $sni_value]] + 5 }] [expr { $sni_length + 3 }] 0 $sni_length $sni_value]
}
I was redirected from this thread (https://devcentral.f5.com/questions/help-with-sni-not-being-passed-to-pool-serverscomment50962) to this one by Stanislas. I was struggling with two certs/two profiles with SNI support. couldn’t make it work. I just tested this irule and it works fine. I wanted to use the default config instead of an irule as I already have a complex irule/apm setup but this solves my issue for the moment. I had a question in mind about how to make it work with two certs but I answered my question with a quick test. I created a client profile (no sni setting defined) and added the two certs ( with only one key otherwise you get the error ‘Client SSL profile cannot contain more than one set of same certificate/key type’). I created a server profile (no sni no cert just inherited from th default ssl server). Pluged the iRule to the VS and voilà ! Cheers ! But I’d like to know if configuring multiple profiles with sni entries (and a default sni profile) on a single VS work !
you can configure on the virtual server multiple clientssl profile (to manage client servername certificate selection) and with only one serverssl profile with this irule.
Stanislas, you’re correct, I expressed myself incorrectly. It’s sending the VS hostname.
I’m using APM with rewrite mode, so I followed your suggestion when I read this thread (I did test Kai’s iRule too). I had the iRule log what it does, so I can see that the hostname that it’s going to inject is the correct one, but in the packet capture I still see the VS hostname.
@angorya, I am seeing the same behavior you are. I have a portal access profile setup to route traffic to an internal app. I used the rule above and the tcpdumps still show the original server name instead of the injected server name.
I am struggling the same as Angorya and Dane to get this working with Portal-Access. Replaced HTTP_Request with ACCESS_ACL_ALLOWED and its still sending the original SNI
653495-1 : Incorrect SNI hostname attached to serverside connections
Component: Local Traffic Manager
Symptoms: SNI hostname submitted to a virtual server on the client side is sent to server side, even if there is a different hostname specified in the server SSL profile.
Conditions: -- Client side ClientHello contains SNI.
Impact: SNI is sent from client to server without stripping or rewriting the SNI.
Seems to be an dead end then, since you can not remove an existing SNI extension from the Handshake for now (see my prequisites Step 3.).
The last chance I see for you is by utilizing a VIP-targeting-VIP setup, so that you can still use SNI to flip SSL Profiles for the client side connection (aka. external VS) while making sure to not forward a SNI value to APM (aka. internal VS). At least this approach will allow you to mitigate the listed condition “Client side ClientHello contains SNI.” and would then allow you to insert a SNI value of your choice on the connection between the internal VS and backend servers.
I have two virtual servers with multiple server ssl profiles applied. One is working, the second only work with one domain. Replacing the multiple server ssl profiles with this irule solved the problem. Thanks!
