GL.iNet GL-MT6000 on KPN fiber

Configuration

Setting up with Dutch KPN fiber

I have tested the Flint 2 (GL-MT6000) with KPN fiber (XGS-PON, 4Gbit). Since this router has 2.5Gbe WAN/LAN ports, you cannot use the full 4Gbit bandwidth if you have a 4GBit subscription.

Requirements:

• Use the Genexis/Nokia ONT provided by KPN. The Flint 2 does not have an SFP+ slot, so it is not possible to hook up directly to fiber.
• KPN requires setting up the internet connection with PPPoE with VLAN tagging. The Flint 2 supports PPPoE with VLAN tagging and can pretty much saturate the full 2.5Gbit interface with hardware offloading enabled. Moreover, this puts the CPU load near zero.

The setup is pretty straightforward. First choose to modify the internet connection on the main page:

On the next page, choose the PPPoE tab. Then set the following:

• Username: internet (can be anything)
• Password: internet (can be anything)
• VLAN ID: 6
• MTU: 1500

Then click Apply.

You are sent back to the main internet overview page and the status will refresh itself several times. If all went well, the connection is usually set up within 30 seconds or so.

On my Flint 2, this didn’t enable IPv6 yet. I resolved this by going to the Network → IPv6 page and making the following changes:

• Enabled IPv6: toggle to enable
• Mode: native
• Click Apply.

There are more steps to do if you want to set up IPTV or telephony, but we don’t use these services, so I haven’t tried this.

Baby jumbo frames

By default the firmware uses an MTU of 1500 for the WAN interface. Since PPPoE adds an 8 byte overhead, the MTU on the PPPoE interface will be 1492, which is considered suboptimal (by some). The issue is that as of writing the main GL.iNet firmware does not support MTUs larger than 1500, so these ‘baby jumbo frames’ are not possible (possibly due to still using kernel 5.x). The OpenWRT 24-based version with open source drivers, however, does support larger MTUs.

Various discussions on Dutch forums suggest:

• 1512 on the WAN interface (to account for VLAN tagging overhead).
• 1508 on the VLAN interface (for the aforementioned PPPoE overhead).
• 1500 on the PPPoE interface.

I have found that LuCI does not allow me to set the MTU on the VLAN interface to a value higher than 1500. So I modified the network configuration in /etc/config/network as follows:

config interface 'wan'
	option force_link '0'
	option classlessroute '0'
	option metric '10'
	option device 'eth1.6'
	option proto 'pppoe'
	option username 'internet'
	option password 'internet'
	option vlanid '6'
	option disabled '0'
	option peerdns '1'
	option ipv6 '1'
	option mtu '1500'

config device
	option name 'eth1.6'
	option type '8021q'
	option ifname 'eth1'
	option vid '6'
	option mtu '1508'
	option mtu6 '1508'

config device
	option name 'eth1'
	option mtu '1512'
	option mtu6 '1512'