FS#4211 - DIR-867: udhcpc fails to get a lease on the WAN port

[openwrt-bot]

dajhorn:

Device: D-Link DIR-867 HW:A1
Software: openwrt-21.02.1-ramips-mt7621-dlink_dir-867-a1-squashfs-factory.bin

Reproducer:

• Install OpenWRT on the DIR-867.
• Set the system configuration to defaults.
• Reboot.
• Wait for a DHCP lease on the WAN port.

I only ever got this message with a timeout and zero bytes inbound:

udhcpc: sending discover

I tried these things:

• Running udhcpc at the console with various options like -T, -C and -B.
• Doing ifconfig up/down on the WAN interface.
• Toggling every DHCP option in LuCI.
• Disabling the firewall.

The ISP is Teksavvy through a Technicolor DOCSIS modem. Any other DHCP client works as expected when directly connected to the modem. Reverting to stock D-Link firmware version 1.30 resolves the glitch.