Correct IP setting when two firewalls connected to one ISP.

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Correct IP setting when two firewalls connected to one ISP.

L4 Transporter

We have two PA's connecting to one ISP. One is just being set up.


The ISP is ""

Route is ""


Is it correct to have both firewall external vlan interfaces as such


FW1 ""

FW2 ""

 Vlan 140






And for the NAT





FW1 Main Nat ""

FW2 Main Nat ""





I ask, because the new firewall is logging packets for the old firewall. I am seeing "x.x.x.99" on the firewall with VIP "x.x.x.122"







Cyber Elite
Cyber Elite

- If your ISP's subnet is , you have usable IP addresses to, so your firewalls would need to have an IP in that range

- your vlans are untagged, you'll want to tag them and use proper vlans on your switches to prevent having one giant, and insecure broadcast domain


are there any other nat rules? it's possible your old firewall has taken ownership of all the IP's in that subnet if there's a NAT policy that allows it

Tom Piens
PANgurus - (co)managed services and consultancy

The IP's were just an obscured example.


Both have the same "/27"  on the interface and is that correct? 

Neither firewall has overlapping NAT IP addresses. the NAT addresses are x.x.x.y/27



I have the VLANS tagged on the aggregate interface, I assume that is sufficient and does not need tagged on the VLAN aswell. The switches are VLANED.







It all seems to be working,


It's just the loggs showing IP's from the other firewall that are the concern.  There's a 3rd Device on that subnet that also connects to the ISP, I don't see it at all in the loggs.




Are you running active/passive or active/active? A/P doesnt need an IP for each firewall as they are shared between the two.



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