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indmax_195288's avatar
indmax_195288
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Mar 04, 2016

regarding tcp profile timeout (configured) vs snat pool timeout (indefinite)

Hi F5 experts, we are running 11.6.0.I would like to clear my understanding regarding tcp profile timeout vs snat pool timeout. if i have a tcp profile idle time out value of 300sec and a indefinite ...
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Hannes_Rapp's avatar
Hannes_Rapp
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Mar 04, 2016

The timeout values as set in TCP profile matter. You may consider SNAT idle timeout values as pseudo-configuration that can be ignored at all times. A bit overstated, but you really can use whatever (i.e. default) SNAT timeout value you like, regardless of the TCP/UDP timeout you want.

 

  • Considering a scenario when SNAT timeout is exceeded and TCP timeout is not exceeded, the TCP session for the client can resume without interruption. F5 will just insert a new SNAT record to its table. Apart from a micro-delay, there's no impact to customer. Just don't set the SNAT idle timeout value too low (i.e. 1 or 2 seconds) as this will increase your CPU usage due to repetitive insertions and removals of SNAT records.

     

  • Assuming default settings, if a TCP profile timeout is exceeded, F5 will respond with TCP/RST in an attempt to hear back from client or server.

     

FYI: The indefinite SNAT timeout configuration is silently capped to 300 seconds. So in reality all SNAT records have a finite timeout value after which they will be removed.