Forum Discussion

Nimbostratus

Feb 09, 2024

TCL errors

Hey Team, We are experiencing some TCL errors with one of our iRules. I didn't build the iRule, but have inherited it from a past engineer, so I don't have a ton of knowledge on the specifics, bu...

application delivery

KeesvandenBos

MVP

Feb 09, 2024

Hi,

The error occurs when the rule1_msg1 variable is empty.
This could happen if a client doesn't complete the 3way handshake and send a reset. Then the CLIENT_CLOSE event is hit without the client sending any data, leaving rule1_msg1 being never created in the other events.

Maybe you can solve this by adding this line in the when RULE_INIT { section

when RULE_INIT {
    set static::http_rule1_dest ""
    set static::http_rule1_tmplt ""
    set rule1_msg1 ""
}

Hope it helps.

Cheers,

Kees

adick

Nimbostratus

Feb 09, 2024

Thanks Kees!

This seems to be a good solution.

Could there be other reasons the CLIENT_CLOSE event could get hit without the client sending data? I'm wondering if this iRule could be causing any problems with the VIPs that it is configured on? I heard from someone when you see TCL errors it usually means the VIP communication was cut off early.

Or if because it only triggers on CLIENT_CLOSE maybe it is something where the client already had problems communicating and this is just the error that triggers when there is another issue present.

Thanks

KeesvandenBos
MVP
Feb 11, 2024
Your welcome.

CLIENT_CLOSED events gets triggers by the client ending the connection. And yes it is true, any TCL error will cause the Virtual Server to stop processing traffic.

rule1_msg1 not being filled with data (and causing the TCL error) will only happen if a client doesn't send any data after the connection has been created, same for SERVER_CLOSED TCL error. If this irule is attached to a virtual server without a proxy profile (L7 connection) the BIG-IP will create the server connection the moment thhttps://my.f5.com/manage/s/article/K8082e client connection is completed. If the client doesn't send any data, in the end the pool member will close its connection with the BIG-IP.
K8082 explains the differences between virtual server types.

It could be a client issue causing these erros' Still it is better to first create an empty variable to make sure you do not run into issues.

Cheers,
Kees