ISR4431 behind Firewalla Purple

[slussj]

I have an isr4431 behind a firewalla purple and can't get my DNS to stay connected. My connection on my test pc flaps from connected to not connected. I can ping and traceroute across internet but can't use DNS to access sites. 

I have DNS servers setup on sub int for my data vlan dhcp pool. DNS server is setup to DNS IP on firewalla and Google as secondary. I've even tried turned off monitoring on firewalla and placing into DMZ, no luck. 

Setting up NAT did help get from test pc to firewalla inside int. 

Network topology is from inside out:

Pc->cat3850->isr4431->netgear unmanaged switch->firewalla purple->isp

Anyone have any experience with this setup? What am I missing with my DNS?

[pieterh]

>>> DNS server is setup to DNS IP on firewalla and Google as secondary <<<
renove the entry of the "DNS IP on firewalla", makint google DNS the primary/only DNS server in your DHCP settings
if then the (google) DNS reachability is stable, then the firewalla does not respond as desired,
=> you need to look at the firewalla configuration,

as this is a Cisco forum , you may need to contact a firewala forum instead

[MHM Cisco World]

Some case FW use dns of ISP' and I talking about cisco fw' there is option to make FW push the dns know by isp to dhcp client.

Check this feature with your fw.

MHM