Multiple VLAN on Wan Interface UDM

About a year ago, I switched to a different ISP offering 8Gbit Fiber. I am happy with this ISP’s service.

However, I have been working on and off on an issue that has been bothering me for the last couple of months.

I’m encountering issues getting my VOIP Client to work with their SIP server.

Some technical details:

  • Internet and IPTV is supplied on VLAN 100.
  • VOIP is supplied on VLAN 102.
  • I’m using a Unifi Dream Machine Pro (UDM) as my router.

I can get a working phone by placing a switch between the ONT and the UDM, using the switch to split the VLAN, and then forwarding VLAN 100 to the UDM and VLAN 102 to a VOIP ATA.

However, because of the switch’s limitations, I’m limited to 1gbps.

Unfortunately, the UDM does not support multiple VLANS on the WAN interface through the UI. It runs an OS, which is a derivative of Debian.

I tried manually creating the interface and the route, but I’m getting stuck. I’m hoping someone here can help me understand what I’m missing or what I am doing wrong.

What I have done:

Created the VLAN 102 Interface on ETH9 (The interface that fiber is coming in on)

ip link add link eth9 name eth9.102 type vlan id 102

ip link set dev eth9.102 up

udhcpc -b -R -s ./voip.hook -i eth9.102

voip.hook contains the following for the bound() action.

    ip -4 addr add $ip/$mask ${broadcast:+broadcast $broadcast} dev $interface
    ip -4 link set dev $interface up

    for i in $dns; do
            echo "nameserver $i"
    done

After running udhcpc I get an IP assigned in the 10.205.16.0/12 Range.

I get the following two nameservers:

  • nameserver 62.45.58.172
  • nameserver 62.45.59.40

I now add a Route to route these two nameservers through the eth9.102 interface.

I tried:

  • ip route add 62.45.59.40/32 dev eth9.102
  • ip route add 62.45.58.172/32 dev eth9.102

If I now try to query the nameservers using nslookup:

nslookup
> server 62.45.59.40
> voice.caiw.net
;; connection timed out: no servers could be reached.

The same happens when I try to use the other DNS server.

I felt I was missing something, but I’m not entirely sure.

Does anyone else have a suggestion?

I know it’s obvious, but your best solution is to just buy a 2.5 Gb switch. Messing with the UDP is only going to cause you more problems down the line - pretty easy for a update to wipe half your changes and leave you with a non-functioning router.