Sonicwall IPS zone

I have Intrusion prevention services on both the WAN and LAN zones on many sonicwall firewalls. I have been trying to find out if it should be on the WAN or the LAN zone. I doubt it should be on both.

I found one document saying it should be on the LAN interface but I can't find any definitive document on Sonicwall's site.

Which zone should I have IPS on?
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Blue Street TechLast KnightCommented:
Hi ajdratch,

Actually, if you want a multi-layered, inter-zone security defense, all the CGSS services (CFS (not on WAN), App Control, GAV, AS, IPS, & SSL Control) should be enabled on all LAN VLANs, WLAN VLANs, and the WAN. By enabling it on each internal Zone it enforces on all incoming and outgoing traffic from that Zone and between each Zone. It's a security best practice. If you are looking for documentation view here:

It's the admin guide for IPS from 2006 but things have only gotten exceedingly more intense regarding security so if they mention it then its the defacto now.

Let me know if you have any other questions!
ajdratchAuthor Commented:
I have been checking on a few heavily used firewalls. When I have it on both zones, the firewall CPU can spike to 100%. I have taken it off and CPU drops to very little. It seems if it protects incoming and outgoing on the zones, it will inspect every packet twice if I have it on LAN and WAN
Blue Street TechLast KnightCommented:
It sounds like your firewall is too old, undersized or something else is going on. We manage about 35 SonicWALLs and have IPS and for that matter all of the available security services enabled on all Zones without any issues or spikes like you are saying.

What model and firmware version are you running?

Reboot the firewall as well.

Regardless, update your firmware to the latest release.
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ajdratchAuthor Commented:
This is a new NSA 220. Up to date firmware. The two sites have large amount of VoIP so that may be causing the problem with IPS
Blue Street TechLast KnightCommented:
Sorry this question slipped through the cracks.

How many users do you have under the NSA 220? It shouldn't max out your CPU unless the firewall was incorrectly sized or misconfigured.

Is there anything in the logs that would indicate that IPS is blocking or detecting anything? IPS should be set to Detect all; Prevent High and Medium only.

Irrespectively, the answer to your question was in my comment above (http:#a40907594).

Let me know how it goes!

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ajdratchAuthor Commented:
IPS was set to  Detect all; Prevent High and Medium only. That may work but in this case I had to turn it off on LAN and WAN so VoIP would work
Rob DuranSystems Network EngineerCommented:
Not sure if you found solution.  I have seen this before where the plane process is maxed out.  I have ran into the following mis-configuration:

Double subnets in a single VLAN..  For example, XO [Default is, which is fine.] then has a virtual interface X0:10 (10.10.10.x) for the main network, which is also fine.  Then X2 (10.10.20.x) ViOP phones then connected to a switch port configured for VLAN 10. And boom! CPU jumps.  ;)

 That said, have you looked at the interface counters on the switches? Specifically queued.

In a multi zone setup you want to enable security services to protect the resources in each zone and from each other.  If you leave it open, one zone can pass bad stuff to another zone.  I would lock it all down and enable services.  You can even enable bi-directional IPS from diag.html hidden page.

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