topic How to enable Ping on ISP interface with Dynamic IP? in General Topics

How to enable Ping on ISP interface with Dynamic IP?

OMatlock — Sun, 02 Apr 2017 22:15:34 GMT

Hi folks,

As I continue my baby step learning, I am successfully using a PA-200 to access the internet from my internal clients.

I am now trying to understand how to enable ping (at least temporarily) on my 1/1 Untrust-L3 interface. I like to be able to ping it from anywhere on the web for troubleshooting and learning purposes.

I am following this article and assigning a ping enabled profile to my interface.

https://live.paloaltonetworks.com/t5/Configuration-Articles/How-to-Allow-Ping-and-ICMP-on-Layer-3-Interface-of-Your-Palo/ta-p/58932

Still unable to ping the public ip address. Am I missing a security rule for ping specifically?

Created a management profile for ping.

Assigned it to my Public interface.

Interface gets its IP from ISP via DHCP. I am trying to ping the public IP address from laptop, 192.168.32.13.

Re: How to enable Ping on ISP interface with Dynamic IP?

TranceforLife — Sun, 02 Apr 2017 22:57:32 GMT

Heys,

You have configured your local ip address (private) to be allowed to send ping requests to the outside interface (with external ip address). This won't work. Please remove your ACL entry and leave it blank. intrazone-default policy in conjunction with mgmt profile will take care of your ping requests:

Re: How to enable Ping on ISP interface with Dynamic IP?

reaper — Mon, 03 Apr 2017 09:26:36 GMT

pinging the external interface from an internal IP is also a little more complex than it may sound

one of the first things that will happen is that your ping is going to hit a NAT rule as it is outbound, so will hit your trust to untrust NAT rule, meaning your source IP will be changed into the interface IP

What happens next, is what makes it more tricky: your translated packet will have the same source and destination IP address, which is technically a LAND attack (because this could cause a loop where a host is constantly replying to itself) so the packet is discarded

To fix this issue you should add a NAT policy above the outbound policy specifically for your external IP where you perform no NAT at all. With a static IP this is a piece of cake as you can easily set a destination IP address, for a dynamic IP this is not possible, so you will need some sort of dynDNS servie which you can add to the firewall as a FQDN object

Re: How to enable Ping on ISP interface with Dynamic IP?

TranceforLife — Mon, 03 Apr 2017 09:41:37 GMT

I was thinking yesterday about this but could not explain it in the right way. Yes ping definitely fails if you are initiating a request from the internal zone. Just tested!

Re: How to enable Ping on ISP interface with Dynamic IP?

OMatlock — Tue, 04 Apr 2017 18:07:57 GMT

Thank you for the feedback! Will close this thread this week.