nix-config/nixos/agares/rules.nft

flush ruleset

define IF_MGMT = "enp1s0"
define IF_FF = "ff.11"
define IF_LAN = "lan.10"
define IF_WAN = "ppp0"
define IF_SRV = "srv.13"

# Modem uses this for internet uplink via our WAN
define IF_MODEM = "enp2s0"

define IF_ROADW = "roadw"

table inet filter {
  # Will give "no such file or directory if hardware does not support flow offloading"
  # flowtable f {
  #   hook ingress priority 0; devices = { enp1s0, enp2s0 }; flags offload;
  # }

  chain input_local {
    ip6 saddr != ::1/128 log prefix "Dropped IPv6 nonlocalhost packet on loopback:" drop
    accept comment "Accept traffic to loopback interface"
  }

  chain input_icmp_untrusted {
    # Allow ICMP echo
    ip protocol icmp icmp type { echo-request } limit rate 1000/second burst 5 packets accept comment "Accept echo request"

    # Allow some ICMPv6
    icmpv6 type { destination-unreachable, packet-too-big, time-exceeded, echo-request, echo-reply, parameter-problem, mld-listener-query, mld-listener-report, mld-listener-done, mld-listener-reduction, nd-router-solicit, nd-router-advert, nd-neighbor-solicit, nd-neighbor-advert, mld2-listener-report } limit rate 1000/second burst 5 packets accept comment "Allow some ICMPv6"
  }

  chain input_modem {
    jump input_icmp_untrusted
  }

  chain input_wan {
    # DHCPv6 client
    meta nfproto ipv6 udp sport 547 accept comment "Allow DHCPv6 client"

    jump input_icmp_untrusted

    udp dport 51234 accept comment "Wireguard roadwarriors"
  }

  chain input_lan {
    counter accept comment "Accept all traffic from LAN"
  }

  chain input_mgmt {
    counter accept comment "Accept all traffic from MGMT"
  }

  chain input_srv {
    counter accept comment "Accept all traffic from services"
  }

  chain input_roadw {
    counter accept comment "Accept all traffic from roadwarriors"
  }

  chain input_ff {
    jump input_icmp_untrusted

    # DHCP
    meta nfproto ipv6 udp dport 547 accept comment "Allow DHCPv6 client"

    # Allow DNS and DHCP from Freifunk
    udp dport { 53, 67 } accept comment "Allow DNS and DHCP from Freifunk"
  }

  chain input_srv {
    jump input_icmp_untrusted

    # DHCP
    meta nfproto ipv6 udp dport 547 accept comment "Allow DHCPv6 client"

    # Allow DNS and DHCP from SRV
    udp dport { 53, 67 } accept comment "Allow DNS and DHCP from services"
  }

  chain input {
    type filter hook input priority filter; policy drop;

    ct state {established, related} counter accept comment "Accept packets from established and related connections"
    ct state invalid counter drop comment "Early drop of invalid packets"

    iifname vmap { lo : accept, $IF_WAN : jump input_wan, $IF_LAN : jump input_lan, $IF_FF : jump input_ff, $IF_ROADW : jump input_roadw, $IF_MODEM : jump input_modem, $IF_MGMT : jump input_mgmt, $IF_SRV : jump input_srv }
  }

# Only works if hardware flow offloading is available
#  chain offload {
#    type filter hook forward priority -100; policy accept;
#    ip protocol tcp flow add @f
#    counter packets 0 bytes 0
#  }

  chain forward {
    type filter hook forward priority filter; policy drop;

    # Accept connections tracked by destination NAT
    ct status dnat counter accept comment "Accept connections tracked by DNAT"

    # TCP options
    tcp flags syn tcp option maxseg size set rt mtu comment "Remove TCP maximum segment size and set a size based on route information"

    # ICMPv6
    icmpv6 type { destination-unreachable, packet-too-big, time-exceeded, echo-request, echo-reply, parameter-problem } limit rate 5/second counter accept comment "Forward up to five ICMP messages of allowed types per second"
    meta l4proto ipv6-icmp accept comment "Forward ICMP in IPv6"

    # mgmt <-> *
    iifname { $IF_LAN, $IF_ROADW } oifname $IF_MGMT counter reject comment "Reject traffic from LAN and roadwarrior to MGMT"
    iifname $IF_MGMT oifname { $IF_LAN, $IF_ROADW } counter reject comment "Reject traffic from MGMT to LAN and roadwarrior"
    # drop (instead of reject) everything else to MGMT

    # LAN, ROADW -> * (except mgmt)
    iifname { $IF_LAN, $IF_ROADW } counter accept comment "Allow all traffic forwarding from LAN and roadwarrior to all interfaces, except to mgmt"

    # FF -> WAN
    iifname { $IF_FF, $IF_SRV } oifname $IF_WAN counter accept comment "Allow all traffic forwarding from Freifunk and services to WAN"

    # { WAN, SRV } -> { FF, LAN, RW, SRV }
    iifname { $IF_WAN, $IF_SRV } oifname { $IF_FF, $IF_LAN, $IF_ROADW, $IF_SRV } ct state established,related counter accept comment "Allow established back from WAN and SRV"

    # WAN -> SRV
    iifname $IF_WAN oifname $IF_SRV tcp dport ssh accept comment "Allow all SSH traffic forwarding from WAN to services"
  }

  chain output {
    type filter hook output priority 100; policy accept;
  }
}

table ip nat {
  chain prerouting {
    type nat hook prerouting priority dstnat; policy accept;
  }

  chain postrouting {
    type nat hook postrouting priority srcnat; policy accept;
    ip saddr { 192.168.96.0/19 } oifname { $IF_WAN } masquerade comment "Masquerade traffic from LANs"
  }
}

table arp filter {
  chain input {
    type filter hook input priority filter; policy drop;
    iifname { $IF_MGMT, $IF_LAN, $IF_FF, $IF_SRV, $IF_MODEM } limit rate 1/second burst 2 packets accept comment "Limit number of ARP messages from LAN, FF, MGMT, SRV, modem"
  }
}