How to configure ingress to Azure Load Balancers with PaloAlto-secured network

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How to configure ingress to Azure Load Balancers with PaloAlto-secured network

L1 Bithead

We have a setup where we're using PaloAlto to secure outbound traffic from Azure. I have two Azure load balancers sitting in front of PaloAlto; "palo-alto-external" in front of the Untrust interface that has a private IP address on the frontend, and "palo-alto-internal" in front of the Trust interface that has a public IP address on the frontend. PaloAlto is used by having a route in the Azure route table sending all 0.0.0.0/0 traffic to the frontend IP of "palo-alto-internal", and then PaloAlto receives the traffic on Trust, it goes through the firewall to Untrust via static routes, and then out to the internet from there. This setup works for the most part. But it's not working for my application Azure load balancers (ie. not the PaloAlto load balancers, actual load balancers for applications) - I cannot resolve any of the public endpoints for them. I know the problem is PaloAlto because when I disable the 0.0.0.0/0 route rule, thus turning off PaloAlto for the network, it works fine and then breaks when I enable it.

 

I've been in contact with Microsoft support and they said the problem is because of "assymetric routing"; because the IP address it goes out through from the network (the "palo-alto-internal" frontend IP) is not the same as the one it comes back in through (the "palo-alto-external" frontend IP), the firewall breaks the load balancer. This is a page from Azure that explains the issue from the perspective of the Azure native firewall although the fix suggested on this page does not work in PaloAlto.

 

I was told from Microsoft that the fix is to "add on the Palo Alto side DNAT/SNAT rules to be able to leave and come back to hit that External AKS Load Balancer" but I don't know how to do that. How is this done?

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