How to troubleshoot CFS v4.0 broken site issues with Wireshark?

06/01/2020 13 4002

DESCRIPTION:

Multiple times administrator run into issue of allowing or whitelisting some sites from CFS filtering of the SonicWall.The simple solution is to allow the website/domain name under Manage |Policies | Object | Content Filter Object | URI List Object

However, some websites fetch data from few other domains and hence whitelisting a single main domain results in partial contents being loaded.

EXAMPLE: If we add 'bbc.com' website only and under the allowed domain  list, the website partially loads as shown below:

RESOLUTION:

In order to fine the assosicated domains or extra domains embedded in the website coding, either we can check the HTML coding by checking 'view page source' of the website or use the 'Packet Monitor' feature of the SonicWall to identify it as explained below:

1. Set the packet capture on the SonicWall based on the source IP address of the PC which is having the issue. You can navigate to Investigate |Tools | Packet Monitor and configure it as :
   
   
   
   
2. Select the  view filter as only drop packets.
   
   
   
   
3. Refresh or access the broken web-page again from the machine through which packet monitoring has been set and you should notice the following drop packets mentioning the drop reason as Enforced Content Filter Policy. Export this data in libpacpng or any wireshark supported format .
   
   
   
   
4. SonicWall CFS policy will block the client hello packet for https site and 'get request' for http sites. For the above example, the website is https based, hence we will filter the wireshark for client hello packets.
   

   TIP: Either you can check the dropped packet number on firewall and directly go to that packet in wireshark by pressing CTRL+G or use the filter with syntax as shown below to see all the client hello packets captured:

     ssl.handshake.type==1
   
   
   
   
5. Open the client Hello packet and navigate to the Server Name field where you will find the exact domain name which needs to be added in the CFS Allowed Domain List .
   
   
   
   NOTE: You might need to check all the client hello packets and find all the domains which are being dropped as CFS.
   
   
   
6. Add all the domains found through the above steps under the CFS allowed domain list. If you see different sub-domains of  a main domain, you may add Wildcard character (*) to the main domain as shown below.
   
   
   
   
7. Access the website now as you should be seeing all the contents loaded as expected.
   
   TIP: Make sure you check in the private window of browser or clear browsing history to avoid any previous cache issues.