In a Check Point firewall, can you please explain what occurs between the POSTIN (I) and PREOUT (o) inspection points?


Between the POSTIN (I) and PREOUT (o) inspection points most of the policy processing/routing is done.

So the question is actually what is not done between POSTIN (I) and PREOUT (o).

This includes (not a complete list, depends on version and implementation):

  • Packet sanity checks - IP options and state checking.
  • VPN decryption/encryption - Packets are decrypted before processing by rule base.
  • SecureXL processing – Packets are accelerated and may bypass POSTIN-PREOUT altogether if packets were already allowed through policy and traffic can be accelerated.

The iIoO is only default inspection points. For a full list of the in/out chain running on your firewalls run fw ctl chain from SPLAT.

Also see this old but still good reference document http://www.checkpoint.com/techsupport/downloads/html/ethereal/fw_monitor_rev1_01.pdf.

Hope this helps.

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