VLAN Tutorial for the Xiaomi BE 3600

First, we need to have SSH enabled, and also configure the router with PPPoE settings via the web interface to later edit the VLAN data, adding what's commented on in the Network and Port_map files.

Network File

config device 'eth0_dev'
    option name 'eth0'

config device 'eth1_dev'
    option ipv6 '1'
    option name 'eth1'

config interface 'loopback'
    option ifname 'lo'
    option proto 'static'
    option ipaddr '127.0.0.1'
    option netmask '255.0.0.0'

config switch 'switch0'
    option name 'switch0'

config switch 'switch1'
    option name 'switch1'
    option enable_vlan '1'

config interface 'lan'
    option ifname 'eth0.1 eth0.2 eth0.3 eth1'
    option force_link '1'
    option type 'bridge'
    option proto 'static'
    option ipaddr '192.168.31.1'
    option netmask '255.255.255.0'
    option multicast_querier '0'
    option igmp_snooping '0'
    option ip6assign '64'
    option macaddr 'XX:XX:XX:XX:XX:XX'

config alias 'lan_alias'
    option interface 'lan'
    option proto 'static'
    option ip6addr 'XXXX:XXXX:XXXX::X'

config interface
    option ifname 'eth0'
    option keepup '1'

config interface 'eth1'
    option ifname 'eth1.6'   ### add the .6 tag (for Movistar in this case)

config interface 'wan_2'
    option disabled '1'
    option proto 'dhcp'
    option ipv6 '0'
    option wantype 'eth'
    option macaddr 'XX:XX:XX:XX:XX:XX'

config interface 'miot'
    option ifname 'wl13'
    option type 'bridge'
    option proto 'static'
    option ipaddr '192.168.32.1'
    option netmask '255.255.255.0'

config switch_vlan 'vlan1'
    option device 'switch1'
    option ports '3 5t'
    option vlan '1'
    option vid '1'

config interface 'eth0_1'
    option ifname 'eth0.1'

config switch_vlan 'vlan2'
    option device 'switch1'
    option ports '2 5t'
    option vlan '2'
    option vid '2'

config interface 'eth0_2'
    option ifname 'eth0.2'

config switch_vlan 'vlan3'
    option device 'switch1'
    option ports '1 5t'
    option vlan '3'
    option vid '3'

config interface 'eth0_3'
    option ifname 'eth0.3'

config interface 'wan6'
    option proto 'dhcpv6'
    option reqaddress 'try'
    option wantype 'eth'
    option reqprefix 'auto'
    option disabled '1'
    
config interface 'wan'
    option proto 'pppoe'
    list dns '1.1.1.1'
    list dns '1.0.0.1'
    option mtu '1500'
    option peerdns '0'
    option wantype 'eth'
    option username 'xxxx'   # PPPoE from company, in this case, Movistar
    option special '0'
    option mru '1480'
    option macaddr 'XX:XX:XX:XX:XX:XX'
    option password 'xxxx'    # PASSWORD
    option last_succeed '1'
    option ipv6 'auto'
    option ifname 'eth1.6'   ### add the .6 tag (for Movistar in this case)
    
    

Port_map File

config common 'settings'
	option ports '1 2 3 4'
	option vlan_type '8021q'
	option last_vlan_type '8021q'

config port '1'
	option service 'lan'
	option speed '1G'
	option link_mode '0'
	option switch 'switch1'
	option cpu_port '5'
	option phy_id '3'
	option base_iface 'eth0'
	option type 'eth'
	option label '1'
	option vid '1'
	option ifname 'eth0.1'

config port '2'
	option service 'lan'
	option speed '1G'
	option link_mode '0'
	option switch 'switch1'
	option cpu_port '5'
	option phy_id '2'
	option base_iface 'eth0'
	option type 'eth'
	option label '2'
	option vid '2'
	option ifname 'eth0.2'

config port '3'
	option service 'lan'
	option speed '1G'
	option link_mode '0'
	option switch 'switch1'
	option cpu_port '5'
	option phy_id '1'
	option base_iface 'eth0'
	option type 'eth'
	option label '3'
	option vid '3'
	option ifname 'eth0.3'

config port '4'
	option service 'wan'
	option speed '2.5G'
	option link_mode '0'
	option base_iface 'eth1'
	option type 'eth'
	option label '4(2.5G)'
	option ifname 'eth1.6'   ### add the .6 tag (for Movistar in this case)

It has been tested and works on the Xiaomi BE3600 Chinese version, thanks to @pitiriguisvi and @Brudalevante for their help.