[SOLVED] An upgrade to the NIC causes serious Internet connection problem

[M1ch23L]

Hi everyone,

Yesterday I changed my old NIC to a 4-port 2.5Gbe Realtek NIC on my DIY router. The weired thing is after changing the NIC, I can't connect to the Internet any more. The OPNSense version number is 23.1

When I tried to visit bing.com, the browser reports the error ERR_NAME_NOT_RESOLVED. Then I guess this is a DNS problem. I tried 3 methods of setting up DNS service:
1. Set DNS servers explicitly under System>Settings>General, while keeping "Allow DNS server list overridden by DHCP/PPP on WAN" unchecked and "Do not use the local DNS service as a nameserver for this system" unchecked.
2. Enable Unbound DNS, leave the DNS server list under System>Settings>General blank, add 1.1.1.1:853#cloudflare-dns.com within DNS over TLS
3. Use whatever DNS the ISP gives: tick the box of "Allow DNS server list to be overridden by DHCP/PPP on WAN", leave custom DNS server list blank, disable Unbound DNS

Unfortunately, all of them failed. The public IP given by PPPoE is shown on the dashboard so that PPPoE is ok; the ping tool in the OPNSense shell failed as well, with an error "unknown host". I am sure that the network itself is ok since I tried to use a hard router to connect to the Internet and it worked.

I also tried to read logs but didn't find any useful info.

I has never set DNS servers and the gateway under the DHCP section. I never enabled Dnsmasq. I only configured IPv4 settings, while left IPv6 ones blank.

I tried to change different NIC interfaces as WAN, but no matter which interface I use no one worked. Basically I tried to go back to my previous workable settings including reinstalling the OPNSense, I still find no way to connect to the Internet and the problem is still the DNS issue.

Can anyone give me some advice on this problem? Thanks.

Kind regards,
Michael