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Endpoint Firewall Blade

Hi CheckMates!

I've got a question regarding the default policy for the Harmony Endpoint Firewall Blade.
Within the "Inbound Traffic" ruleset, a default rule is one which allows *inbound* UDP on ports 67 and 68, seemingly for purposes of DHCP/BOOTP based IP acquisition.

Why exactly is this rule necessary? I've spent the morning testing and DHCP seems to work just fine as long as I permit outbound UDP 67 broadcasts.

If there's something I'm missing regarding DHCP/BOOTP and general FW blade operation please do tell, I just want to avoid keeping things open unless they have to be.


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2 Replies

Have you tested both interim renewal and lease expiry workflows in addition to the initial lease acquisition, presume none of the target machines are DHCP servers themselves?

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The test machine(s) are Windows 10 Pro patched to 22H2, the DHCP server is a Mikrotik hAP series.

The following workflows work

1) DHCP IP acquisition while connected to the network during boot/reboot
This one is rather clear as DHCP seems to occur prior to the Firewall service being up

2) DHCP IP acquisition after fully booting the system and connecting it to the network once on-desktop with CHKP agent services verified to be running

3) DHCP IP forced re-acquisition through ipconfig /release, ipconfig /renew

4) Permitting the client to sit idle on desktop, waiting for DHCP lease expiry
In this instance the lease length is periodically extended without issue.

5) Changing the STATIC DHCP lease IP address on the DHCP server
After a period the IP on the client is automatically retrieved.

Another thing that comes to mind would be RFC 3203 - DHCP reconfigure extension which would allow the DHCP server to force-expire a DHCP lease by sending a Unicast message to the client. But I'm not sure where this option is actually implemented/supported.

My Client & Server are also both on the same network; would the workflow differ if a DHCP relay is configured?


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