Lost Traffic / Packets Disappear

From PFSenseDocs

If you encounter issues with traffic being lost, or packets that seem to disappear or never show up (or leave) an interface, try disabling Checksum Offloading as follows:

• Click System > Advanced
• Check "Disable Hardware Checksum Offloading" near the bottom of the page, under the Hardware Options header.

Click save, and try again. You may want to reboot after applying this option, but it should not be necessary.

This has historically been an issue with Realtek NICs but has also been seen in some scenarios with Via Rhine NICs and some specific Intel fxp cards.

It may also manifest itself as a PPPoE connection that will establish a login and bring up the interface, but will not pass traffic.