Destination NAT is not working when PBF for dual ISP is enabled

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Destination NAT is not working when PBF for dual ISP is enabled

L1 Bithead

Hi All,


I followed the guide at this URL to setup the Dual ISP for outbound access.


I have set the http/https services to use ISP 2 and other traffic to use ISP 1. It is working find and the redundancy also working fine.


However, I have 2 web services that hosting using ISP 1. I have setup the destination NAT and required policy but it is not working when the 2 ISP link is up. If i disconnect the ISP 2, the destination NAT is working fine.


I also tried to setup the PBF rule for Symmetric Return using ISP 1 using the following guide.


The log details when the Dual ISP + Symmetric PBF is define. It just showed incomplete and aged-out. From Client wireshark, it keep resending the TCP transmission.

hosting not ok when isp 1 up OK.png

The result when disable the PBF for Symmetric returna and disconnect ISP 2.

hosting ok when isp 1 down OK.png


Is there any other thing I need to do in order to allow dual ISP and destination NAT to work? Appreciate if someone can give me a hint on this.


L7 Applicator

I think you will need to modify your PBF filter rule for the web server to work.  What might be happening is the http/https traffic from the server in reply to the inbound dNAT is being picked up and sent to ISP 2.


Add to that filter a negate ip address source for the internal address of your web server so that it is not covered by the forwarding filter.


Steve Puluka BSEET - IP Architect - DQE Communications (Metro Ethernet/ISP)
ACE PanOS 6; ACE PanOS 7; ASE 3.0; PSE 7.0 Foundations & Associate in Platform; Cyber Security; Data Center

I figure out the problem.


When i added the PBR for this destination NAT, i did not specific the next hope. The Interface and Server VLAN are different. That why.

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