I have a new RUTX11 recently installed, with 2 WAN connections (both hardwired Ethernet). Firmware is 7.10.2.
TL;DR
After a reboot, RUT fails to get a DHCP lease from the modem attached to LAN3 port that’s configured as a WAN (port-based VLAN).
WAN1
Connected to the WAN port is a Verizon 5G modem/router combo device in IPPT passthru mode. RUT WAN is in DHCP mode, and the Verizon device provides a public IP (not CGNAT) to the RUT. Works fine.
WAN2 (the problem)
A few days later, Spectrum came and installed a Hitron EN2251 DOCSIS modem to provide 600M service as the new primary WAN. Since the dedicated WAN port was already occupied, and I was not on-site, I had the installer connect his cable to Eth3, and VLAN’d it so I could set it up as a WAN interface. Screenshot:
This connection is also configured in DHCP mode, and provides a real routable public IP. Great!
UNTIL I had to reboot the RUT. After doing so, the Spectrum WAN went down and appeared offline. Checking the interface details, it was not receiving an IP via DHCP from the Hitron modem. I ran some tcpdump traces and saw lots of ARP “who has x.x.x.x?” packets flying across the wire, but the RUT’s DHCP REQUEST packets were completely ignored.
The only way to “fix” this was to reboot the Hitron device… it MUST boot or be connected AFTER the RUT has booted, or it fails. I assume this is because during the RUT boot sequence, before it has loaded the switch0 config, it momentarily “sees” some traffic it does not like from the other LAN devices (too many MAC addresses, conflicting subnet, multiple DHCP requests etc) and thus blocks all further access and denies the DHCP lease. This may or may not be a bug or out-of-spec implementation on the Hitron, but it is what it is and I can’t change it.
My questions
- Anyone else seen this behavior?
- Is there any workaround? Can I somehow block or shut down the port during boot to avoid this?
Btw, since discovering this issue, I’ve reversed the cables, so the Spectrum/Hitron is on the “real” WAN port, and the Verizon 5G modem is on the VLAN’ed Eth3 port. It seems happy like this, so it’s definitely an edge case with the Hitron. Still would love to know if there’s any way to make this work since I’m likely to encounter this scenario again.