I have swapped pluging HKT (with IPv6) into eth0 (the original WAN port).
Now IPv6 works.
Thank you very much for your help @hansome .
I am sorry.
I have tried accessing 192.168.50.1 / 192.168.55.1 only when I was testing last time.
I have just found when I am connecting to eth2 (192.168.55.0/24), I cannot access 192.168.50.2.
/etc/config/network
config interface 'loopback'
option device 'lo'
option proto 'static'
option ipaddr '127.0.0.1'
option netmask '255.0.0.0'
config globals 'globals'
option ula_prefix 'fdfa:43aa:ca04::/48'
config device
option name 'br-lan'
option type 'bridge'
option multicast_to_unicast '0'
list ports 'eth3'
list ports 'eth4'
config device
option name 'eth1'
option macaddr '94:83:c4:18:9d:18'
config device
option name 'eth2'
option macaddr '94:83:c4:18:9d:18'
config device
option name 'eth3'
option macaddr '94:83:c4:18:9d:18'
config device
option name 'eth4'
option macaddr '94:83:c4:18:9d:18'
config interface 'lan'
option device 'br-lan'
option proto 'static'
option netmask '255.255.255.0'
option isolate '0'
option ipaddr '192.168.50.1'
option ip6assign '64'
option ip6hint '0000'
option ip6ifaceid '::1'
option metric '128'
config device
option name 'eth0'
option macaddr '94:83:c4:18:9d:17'
config interface 'wan'
option device 'eth0'
option proto 'dhcp'
option ipv6 '1'
list dns '1.1.1.1'
list dns '1.0.0.1'
option peerdns '0'
config interface 'wan6'
option proto 'dhcpv6'
option device '@wan'
option disabled '0'
option reqprefix 'auto'
option reqaddress 'try'
option peerdns '0'
config switch
option name 'switch0'
option reset '0'
option enable_vlan '0'
config interface 'tethering6'
option proto 'dhcpv6'
option device '@tethering'
option disabled '0'
config interface 'wwan6'
option proto 'dhcpv6'
option device '@wwan'
option disabled '0'
config interface 'guest'
option force_link '1'
option type 'bridge'
option proto 'static'
option ipaddr '192.168.9.1'
option netmask '255.255.255.0'
option multicast_querier '1'
option igmp_snooping '0'
option isolate '0'
option bridge_empty '1'
option ip6prefix 'ddfa:43aa:ca04::/48'
option ip6assign '64'
option ip6hint '0001'
option ip6ifaceid '::1'
option ip6class 'guest'
config interface 'wwan'
option proto 'dhcp'
config rule 'policy_bypass_vpn'
option mark '0x60000/0x60000'
option lookup '53'
option priority '53'
config rule 'policy_via_vpn'
option mark '0x80000/0x80000'
option lookup '52'
option priority '52'
config rule 'policy_dns'
option mark '0x100000/0x100000'
option lookup '51'
option priority '51'
config interface 'wgserver'
option proto 'wgserver'
option config 'main_server'
option disabled '0'
config interface 'HGC4'
option device 'eth1'
option proto 'dhcp'
list dns '1.1.1.1'
list dns '1.0.0.1'
option peerdns '0'
option ip4table '100'
config device
list ports 'eth2'
option type 'bridge'
option name 'br-hgc'
config interface 'HGC'
option device 'br-hgc'
option proto 'static'
option netmask '255.255.255.0'
option ipaddr '192.168.55.1'
option type 'bridge'
option multicast_querier '1'
option igmp_snooping '0'
option isolate '0'
option bridge_empty '1'
option ip6assign '64'
option ip6hint '0002'
option ip6ifaceid '::1'
config rule
option in 'HGC'
option priority '100'
option lookup '100'
/etc/config/firewall
config defaults
option input 'ACCEPT'
option output 'ACCEPT'
option forward 'REJECT'
option synflood_protect '1'
config zone
option name 'lan'
option input 'ACCEPT'
option output 'ACCEPT'
option forward 'ACCEPT'
list network 'lan'
config zone
option input 'ACCEPT'
option name 'lanhgc'
option output 'ACCEPT'
list network 'HGC'
option forward 'ACCEPT'
config zone
option name 'wan'
option output 'ACCEPT'
option forward 'REJECT'
option mtu_fix '1'
option input 'DROP'
option masq '1'
list network 'wan'
list network 'wan6'
list network 'wwan'
config forwarding
option src 'lan'
option dest 'wan'
config rule
option name 'Allow-DHCP-Renew'
option src 'wan'
option proto 'udp'
option dest_port '68'
option target 'ACCEPT'
option family 'ipv4'
config rule
option name 'Allow-Ping'
option src 'wan'
option proto 'icmp'
option icmp_type 'echo-request'
option family 'ipv4'
option target 'ACCEPT'
config rule
option name 'Allow-IGMP'
option src 'wan'
option proto 'igmp'
option family 'ipv4'
option target 'ACCEPT'
config rule
option name 'Allow-DHCPv6'
option src 'wan'
option proto 'udp'
option src_ip 'fc00::/6'
option dest_ip 'fc00::/6'
option dest_port '546'
option family 'ipv6'
option target 'ACCEPT'
config rule
option name 'Allow-MLD'
option src 'wan'
option proto 'icmp'
option src_ip 'fe80::/10'
list icmp_type '130/0'
list icmp_type '131/0'
list icmp_type '132/0'
list icmp_type '143/0'
option family 'ipv6'
option target 'ACCEPT'
config rule
option name 'Allow-ICMPv6-Input'
option src 'wan'
option proto 'icmp'
list icmp_type 'echo-request'
list icmp_type 'echo-reply'
list icmp_type 'destination-unreachable'
list icmp_type 'packet-too-big'
list icmp_type 'time-exceeded'
list icmp_type 'bad-header'
list icmp_type 'unknown-header-type'
list icmp_type 'router-solicitation'
list icmp_type 'neighbour-solicitation'
list icmp_type 'router-advertisement'
list icmp_type 'neighbour-advertisement'
option limit '1000/sec'
option family 'ipv6'
option target 'ACCEPT'
config rule
option name 'Allow-ICMPv6-Forward'
option src 'wan'
option dest '*'
option proto 'icmp'
list icmp_type 'echo-request'
list icmp_type 'echo-reply'
list icmp_type 'destination-unreachable'
list icmp_type 'packet-too-big'
list icmp_type 'time-exceeded'
list icmp_type 'bad-header'
list icmp_type 'unknown-header-type'
option limit '1000/sec'
option family 'ipv6'
option target 'ACCEPT'
config rule
option name 'Allow-IPSec-ESP'
option src 'wan'
option dest 'lan'
option proto 'esp'
option target 'ACCEPT'
config rule
option name 'Allow-ISAKMP'
option src 'wan'
option dest 'lan'
option dest_port '500'
option proto 'udp'
option target 'ACCEPT'
config rule
option name 'Support-UDP-Traceroute'
option src 'wan'
option dest_port '33434:33689'
option proto 'udp'
option family 'ipv4'
option target 'REJECT'
option enabled 'false'
config include
option path '/etc/firewall.user'
config include 'nat6'
option path '/etc/firewall.nat6'
option reload '1'
config rule 'process_mark'
option name 'process_mark'
option dest '*'
option proto 'all'
option extra '-m owner --gid-owner 65533'
option target 'MARK'
option set_xmark '0x80000/0x80000'
config rule 'wan_in_conn_mark'
option name 'wan_in_conn_mark'
option src 'wan'
option dest '*'
option set_xmark '0x80000/0x80000'
option target 'MARK'
option extra '-j CONNMARK --set-xmark 0x80000/0x80000'
option enabled '1'
config rule 'lan_in_conn_mark_restore'
option name 'lan_in_conn_mark_restore'
option src 'lan'
option dest '*'
option set_xmark '0x80000/0x80000'
option target 'MARK'
option extra '-m connmark --mark 0x80000/0x80000 -j CONNMARK --restore-mark'
option enabled '1'
config rule 'out_conn_mark_restore'
option name 'out_conn_mark_restore'
option dest '*'
option set_xmark '0x80000/0x80000'
option target 'MARK'
option extra '-m connmark --mark 0x80000/0x80000 -j CONNMARK --restore-mark'
option enabled '1'
config include 'gls2s'
option type 'script'
option path '/var/etc/gls2s.include'
option reload '1'
config include 'glblock'
option type 'script'
option path '/usr/bin/gl_block.sh'
option reload '1'
config zone
option forward 'REJECT'
option name 'wanhgc'
option output 'ACCEPT'
list network 'HGC4'
option input 'DROP'
option masq '1'
option mtu_fix '1'
config zone
option name 'guest'
option forward 'REJECT'
option output 'ACCEPT'
option input 'REJECT'
list network 'guest'
config forwarding
option src 'guest'
option dest 'wan'
config rule
option name 'Allow-DHCP'
option src 'guest'
option target 'ACCEPT'
option proto 'udp'
option dest_port '67-68'
config rule
option name 'Allow-DNS'
option src 'guest'
option target 'ACCEPT'
option proto 'tcp udp'
option dest_port '53'
config include 'vpn_server_policy'
option type 'script'
option path '/etc/firewall.vpn_server_policy.sh'
option reload '1'
option enabled '1'
config rule 'wgserver_allow'
option name 'wgserver_allow'
option target 'ACCEPT'
option src 'wan'
option proto 'udp tcp'
option family 'ipv4'
option dest_port '51820'
option enabled '1'
config zone 'wgserver'
option name 'wgserver'
option output 'ACCEPT'
option mtu_fix '1'
option masq '1'
option masq6 '1'
option enabled '1'
option forward 'REJECT'
option input 'ACCEPT'
list network 'wgserver'
config forwarding 'wgserver2wan'
option src 'wgserver'
option dest 'wan'
option enabled '1'
config forwarding 'lan2wgserver'
option src 'lan'
option dest 'wgserver'
option enabled '1'
config rule 'glipv6_guest_dhcp'
option name 'Allow-DHCP-IPV6'
option src 'guest'
option target 'ACCEPT'
option proto 'udp'
option dest_port '546:547'
option family 'ipv6'
config rule 'glipv6_guest_icmp'
option name 'Allow-ICMP-IPV6'
option src 'guest'
option target 'ACCEPT'
option proto 'icmp'
option dest_port '58'
option family 'ipv6'
config redirect 'adguard_home'
option name 'Adguard Home'
option src 'lan'
option src_dport '53'
option dest 'lan'
option dest_port '3053'
option proto 'tcpudp'
config redirect 'adguard_home_guest'
option name 'Adguard Home guest'
option src 'guest'
option src_dport '53'
option dest 'guest'
option dest_port '3053'
option proto 'tcpudp'
config forwarding 'wgserver2lan'
option src 'wgserver'
option dest 'lan'
option enabled '1'
config forwarding
option dest 'wanhgc'
option src 'lanhgc'
config forwarding
option dest 'wgserver'
option src 'lanhgc'
config forwarding
option dest 'wanhgc'
option src 'guest'
config forwarding
option dest 'lanhgc'
option src 'wgserver'
config forwarding
option dest 'wanhgc'
option src 'wgserver'
config redirect
option src 'lanhgc'
option name 'AdGuard'
option target 'DNAT'
option dest 'lan'
option dest_port '3053'
option src_dport '53'
config forwarding
option dest 'lanhgc'
option src 'lan'
config forwarding
option dest 'lan'
option src 'lanhgc'
/etc/config/dhcp
config dnsmasq
option domainneeded '1'
option localise_queries '1'
option local '/lan/'
option domain 'lan'
option expandhosts '1'
option authoritative '1'
option readethers '1'
option leasefile '/tmp/dhcp.leases'
option localservice '1'
option ednspacket_max '1232'
option rebind_protection '0'
option noresolv '1'
list server '127.0.0.1#3053'
list server '::1#3053'
config dhcp 'lan'
option interface 'lan'
option start '100'
option limit '150'
option leasetime '12h'
option dhcpv4 'server'
option ra_slaac '1'
option force '1'
option dhcpv6 'relay'
option ra 'relay'
option ndp 'relay'
config dhcp 'wan'
option interface 'wan'
option ignore '1'
config odhcpd 'odhcpd'
option maindhcp '0'
option leasefile '/tmp/hosts/odhcpd'
option leasetrigger '/usr/sbin/odhcpd-update'
option loglevel '4'
config domain
option name 'console.gl-inet.com'
option ip '192.168.50.1'
config dhcp 'guest'
option interface 'guest'
option start '100'
option limit '150'
option leasetime '12h'
option dhcpv6 'server'
option ra 'server'
option ra_management '1'
option ra_default '1'
list dns 'ddfa:43aa:ca04:0001:0000:0000:0000:0001'
list ra_flags 'other-config'
list ra_flags 'managed-config'
config dhcp 'wan6'
option interface 'wan6'
option dhcpv6 'relay'
option ra 'relay'
option ndp 'relay'
option master '1'
list ra_flags 'none'
config dhcp 'wwan6'
option interface 'wwan6'
option dhcpv6 'relay'
option ra 'relay'
option ndp 'relay'
option master '1'
config dhcp 'tethering6'
option interface 'tethering6'
option dhcpv6 'relay'
option ra 'relay'
option ndp 'relay'
option master '1'
config dhcp 'HGC'
option start '100'
option leasetime '12h'
option limit '150'
option interface 'HGC'
option dhcpv4 'server'
option ra_slaac '1'
option force '1'
option dhcpv6 'relay'
option ra 'relay'
option ndp 'relay'
config dhcp 'HGC4'
option ignore '1'
option interface 'HGC4'
list ra_flags 'none'