When Lan1 is connected, it uses eth1. When other Lan ports are used, it uses eth0. If I connect to the WAN port, it still uses eth0. Basically, what has happened is that Lan2, Lan3, Lan4 and WAN ports are being used as LAN and Lan1 is being used as WAN.
This is from system log when connected with Lan1 and then with Lan2:
Mon Jun 26 22:07:55 2023 daemon.notice netifd: Network device 'eth1' link is up
Mon Jun 26 22:07:55 2023 daemon.notice netifd: Interface 'wan' has link connectivity
Mon Jun 26 22:07:55 2023 daemon.notice netifd: Interface 'wan' is setting up now
Mon Jun 26 22:07:55 2023 daemon.notice netifd: Interface 'wan6' has link connectivity
Mon Jun 26 22:07:55 2023 daemon.notice netifd: Interface 'wan6' is setting up now
Mon Jun 26 22:07:55 2023 daemon.notice netifd: wan (6766): udhcpc: started, v1.25.1
Mon Jun 26 22:07:55 2023 daemon.notice netifd: wan (6766): udhcpc: sending discover
Mon Jun 26 22:07:58 2023 daemon.notice netifd: wan (6766): udhcpc: sending discover
Mon Jun 26 22:08:01 2023 daemon.notice netifd: wan (6766): udhcpc: sending discover
Mon Jun 26 22:08:49 2023 daemon.notice netifd: Network device 'eth1' link is down
Mon Jun 26 22:08:49 2023 daemon.notice netifd: Interface 'wan' has link connectivity loss
Mon Jun 26 22:08:49 2023 daemon.notice netifd: Interface 'wan6' has link connectivity loss
Mon Jun 26 22:08:49 2023 daemon.notice netifd: wan (6766): udhcpc: received SIGTERM
Mon Jun 26 22:08:51 2023 daemon.notice netifd: Network device 'eth0' link is up
Mon Jun 26 22:08:51 2023 daemon.info dnsmasq-dhcp[1341]: DHCPDISCOVER(br-lan) 18:60:24:42:4d:6e
Mon Jun 26 22:08:51 2023 daemon.info dnsmasq-dhcp[1341]: DHCPOFFER(br-lan) 192.168.1.151 18:60:24:42:4d:6e
Mon Jun 26 22:08:51 2023 daemon.info dnsmasq-dhcp[1341]: DHCPREQUEST(br-lan) 192.168.1.151 18:60:24:42:4d:6e
Mon Jun 26 22:08:51 2023 daemon.info dnsmasq-dhcp[1341]: DHCPACK(br-lan) 192.168.1.151 18:60:24:42:4d:6e DESKTOP-P5U1Q18
Mon Jun 26 22:08:51 2023 daemon.notice odhcpd[753]: Got DHCPv6 request
Mon Jun 26 22:08:51 2023 daemon.warn odhcpd[753]: DHCPV6 SOLICIT IA_NA from 000100012441c58c186024424d6e on br-lan: ok fd23:458c:4258::714/128
Mon Jun 26 22:08:51 2023 daemon.info dnsmasq[1341]: read /etc/hosts - 4 addresses
Mon Jun 26 22:08:51 2023 daemon.info dnsmasq[1341]: read /tmp/hosts/odhcpd - 0 addresses
Mon Jun 26 22:08:51 2023 daemon.info dnsmasq[1341]: read /tmp/hosts/dhcp.cfg02411c - 2 addresses
Mon Jun 26 22:08:51 2023 daemon.info dnsmasq-dhcp[1341]: read /etc/ethers - 0 addresses
Mon Jun 26 22:08:51 2023 daemon.notice odhcpd[753]: Got DHCPv6 request
Mon Jun 26 22:08:51 2023 daemon.warn odhcpd[753]: DHCPV6 SOLICIT IA_NA from 000100012441c58c186024424d6e on br-lan: ok fd23:458c:4258::714/128
Mon Jun 26 22:08:51 2023 daemon.info odhcpd[753]: Using a RA lifetime of 0 seconds on br-lan
Mon Jun 26 22:08:52 2023 daemon.notice odhcpd[753]: Got DHCPv6 request
Mon Jun 26 22:08:52 2023 daemon.warn odhcpd[753]: DHCPV6 REQUEST IA_NA from 000100012441c58c186024424d6e on br-lan: ok fd23:458c:4258::714/128
Mon Jun 26 22:08:52 2023 daemon.info dnsmasq[1341]: read /etc/hosts - 4 addresses
Mon Jun 26 22:08:52 2023 daemon.info dnsmasq[1341]: read /tmp/hosts/odhcpd - 1 addresses
Mon Jun 26 22:08:52 2023 daemon.info dnsmasq[1341]: read /tmp/hosts/dhcp.cfg02411c - 2 addresses
Mon Jun 26 22:08:52 2023 daemon.info dnsmasq-dhcp[1341]: read /etc/ethers - 0 addresses
Mon Jun 26 22:08:55 2023 daemon.info odhcpd[753]: Using a RA lifetime of 0 seconds on br-lan
Mon Jun 26 22:08:59 2023 daemon.info odhcpd[753]: Using a RA lifetime of 0 seconds on br-lan
Mon Jun 26 22:09:13 2023 daemon.err uhttpd[996]: dmesg: klogctl: Function not implemented
Mon Jun 26 22:10:09 2023 daemon.notice netifd: Network device 'eth0' link is down
This brings me to the firmware I have flashed from:
https://forum.openwrt.org/t/update-lede-17-01-6-custom-builds-for-tp-link-wr841n-d-wr941n-d-wr743n-d-wr741n-d-wr740n-d-all-versions/20638
I have flashed Wr740N v5 firmware. This v5 firmware I think is not the same as the v5 in China. So I have to dig into this a little more.