Unable to Access Some Websites
From pfSense Documentation
If some sites will load, but other sites will not, there are a few possible causes.
- Check all of the items listed on Connectivity Troubleshooting before proceeding
- Ensure the WAN gateway is reachable and set to the proper address
- Ensure the subnet mask on the WAN interface of the firewall is correct
- Ensure the subnet mask on the client stations and on every interface (and VPN) on pfSense is correct
- Ensure the WAN MTU is properly set (See here to determine the MTU), use MSS to lower the MTU if necessary
- Use traceroute to determine where the traffic stops. It may be an upstream connectivity issue and not the pfSense firewall or ISP.
- Disable hardware checksums and see if the problem disappears
- Disable any proxy package such as squid that is in use (if any)
- Check Clear invalid DF bits instead of dropping the packets on System > Advanced, Firewall/NAT tab.
- Check Disable Firewall Scrub on System > Advanced, Firewall/NAT tab.