Traffic hitting policy rule it shouldn't

[Jonathanct]

Hi,

PanOS 9.1.0

I need to block traffic to certain websites and domains.

I created a URL Category object and put just one site inside (example.com).

I then created a firewall rule like this:

Source zone: LAN

Source address: any

Dest Zone: WAN

Dest address: any

Application: any

Service/URL Category: my URL Category Object

Action: ALLOW

(I put it on Allow because for at first I just wanted to check what traffic is hitting this rule).

I immediately noticed a very high hit count on the rule and when I viewed the rule logs I noticed it is allowing loads of traffic that doesn't relate to example.com

I'm affraid if I put this rule to Block it will block my outgoing traffic.

What am I missing 

[Jonathanct]

So I changed it to 'www.sega.com' and it worked! thanks! 🙂

So if I was asked to block domains such as abc.com, def.com, ghe.com etc., I must put 'www' at the begining if it's not actually necessery for normal browsing?

Also, does using URL category in policy rules make the PaloAlto perform a reverse DNS lookup on each packet going through the system? and if so doesn't it have a big impact on performace?

[TravisC · Accepted solution]

The URL is defined by website. In the case of an HTTP request to 'sega.com', the website responds with a 301 (Permanently Moved) to 'www.sega.com'. If you are using Chrome, it will hide the 'www.', but if you click on it will show it. If you use Firefox, you will see that you put in 'sega.com' and then it is changed to 'www.sega.com'. You can use Developer tools on either browser to see what the URL should be by following the request URL.

The firewall doesn't attempt to do a reverse DNS lookup on URL categories. The URL is determined by looking by looking at the HTTP headers, the SSL Client Hello SNI, and SSL Server Hello Common Name (CN) of the Server Certificate Subject DN. This behavior changes if SSL decryption is used.

https://knowledgebase.paloaltonetworks.com/KCSArticleDetail?id=kA10g000000ClzlCAC