A basic nftables config. Only accept ssh, http and https.

nftables.conf

#!/usr/bin/nft -f
# ipv4/ipv6 Simple & Safe Firewall
# you can find examples in /usr/share/nftables/

table inet filter {
  chain input {
    type filter hook input priority 0;

    # allow established/related connections
    ct state {established, related} accept

    # early drop of invalid connections
    ct state invalid drop

    # allow from loopback
    iifname lo accept

    # allow icmp
    ip protocol icmp accept
    ip6 nexthdr icmpv6 accept

    # allow ssh,http
    tcp dport {ssh,http,https} accept

    # allow n2o
    tcp dport 8001 accept

    # everything else
    reject with icmp type port-unreachable
  }
  chain forward {
    type filter hook forward priority 0;
    drop
  }
  chain output {
    type filter hook output priority 0;
  }

}

# vim:set ts=2 sw=2 et:

I can't access the router