Nftables Firewall Basis Konfiguration

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Die Basis Konfiguration

  • Die Basiskonfiguration besagt das von der Firewall nach aussen alles erlaubt ist.
  • Wir schalten hier auch noch den 22 Zugang frei.
#!/usr/sbin/nft -f
flush ruleset
define local_tcp_ports = { 22 }
define save_interfaces = { enp0s8, enp0s9, enp0s10 }

table inet filter {
       chain input {
               type filter hook input priority filter; policy drop;
               ct state established,related accept
               ct state new iif "lo" accept
               ct state new tcp dport $local_tcp_ports accept
       }

       chain forward {
               type filter hook forward priority filter; policy drop;
                 ct state established,related accept
       }
       chain output {
               type filter hook output priority filter; policy drop;
               ct state established,related accept
               ct state new accept
       }

}

Weiter gehts

  • Wir schalten die lokalen Netze gegenseitig frei.
  • So wie auch den Zugriff auf unsere Firewall
  • In der Praxis sollte man das genau überlegen.
  • Für unsere Übung ist das aber ok.
#!/usr/sbin/nft -f
flush ruleset
define local_tcp_ports = { 22 }
define save_interfaces = { enp0s8, enp0s9, enp0s10 } 
table inet filter {
       chain input {
               type filter hook input priority filter; policy drop;
               ct state established,related accept
               ct state new iif "lo" accept
               ct state new tcp dport $local_tcp_ports accept
               ct state new iif $save_interfaces accept
       }

       chain forward {
               type filter hook forward priority filter; policy drop;
               ct state established,related accept
               ct state new iif $save_interfaces accept
               }
       chain output {
               type filter hook output priority filter; policy drop;
               ct state established,related accept
               ct state new accept
       }
 
}

Das Logging

  • Kurz vor dem erreichen der Default Policy wird geloggt
#!/usr/sbin/nft -f
flush ruleset
define local_tcp_ports = { 22 }
define save_interfaces = { enp0s8, enp0s9, enp0s10 } 
table inet filter {
       chain input {
               type filter hook input priority filter; policy drop;
               ct state established,related accept
               ct state new iif "lo" accept
               ct state new tcp dport $local_tcp_ports accept
               ct state new iif $save_interfaces accept
               log prefix "--nftables-drop-input--"
       }

       chain forward {
               type filter hook forward priority filter; policy drop;
               ct state established,related accept
               ct state new iif $save_interfaces accept
               log prefix "--nftables-drop-forward--" 
               }
       chain output {
               type filter hook output priority filter; policy drop;
               ct state established,related accept
               ct state new accept
               log prefix "--nftables-drop-output--"
       }
 
}

Wir gucken

  • tail -f /var/log/syslog | grep nft

Feb 28 17:30:09 firewall kernel: [ 2119.005002] --nftables-drop-input--IN=enp0s9 OUT= MAC=08:00:27:08:29:61:08:00:27:47:d1:33:08:00 SRC=172.16.100.151 DST=172.16.100.1 LEN=356 TOS=0x10 PREC=0xC0 TTL=64 ID=35132 PROTO=ICMP TYPE=3 CODE=3 [SRC=172.16.100.1 DST=172.16.100.151 LEN=328 TOS=0x10 PREC=0x00 TTL=128 ID=0 PROTO=UDP SPT=67 DPT=68 LEN=308 ]

Wir Snaten

  • Wir müssen hier eine neue Tabelle anlegen
  • Snat gehört zur nat-Tabelle
  • Wir müssen das Paket verändern kurz vor dem verlassen des Rechners
  • Der richtige Ort ist der postrouting Haken
#!/usr/sbin/nft -f
flush ruleset
define local_tcp_ports = { 22 }
define save_interfaces = { enp0s8, enp0s9, enp0s10 } 
define wandev = enp0s3
define wanip = 192.168.6.100
define lan-nets = { 172.16.100.0/24 , 172.17.100.0/24 }
table inet filter {
       chain input {
               type filter hook input priority filter; policy drop;
               ct state established,related accept
               ct state new iif "lo" accept
               ct state new tcp dport $local_tcp_ports accept
               ct state new iif $save_interfaces accept
               log prefix "--nftables-drop-input--"
       }

       chain forward {
               type filter hook forward priority filter; policy drop;
               ct state established,related accept
               ct state new iif $save_interfaces accept
               log prefix "--nftables-drop-forward--" 
               }
       chain output {
               type filter hook output priority filter; policy drop;
               ct state established,related accept
               ct state new accept
               log prefix "--nftables-drop-output--"
       }
 
}
table inet nat {
   chain postrouting {
       type nat hook postrouting priority srcnat; policy accept;
       oif $wandev ip saddr $lan-nets snat ip to $wanip
    }
}

Der Counter

  • Man kann auch Counter einbauen.
  • Diese sind im Vorgänger iptables automatisch dabei
  • Es werden Pakete und Bytes gezählt.
#!/usr/sbin/nft -f
flush ruleset
define local_tcp_ports = { 22 }
define save_interfaces = { enp0s8, enp0s9, enp0s10 }
define wandev = enp0s3
define wanip = 192.168.6.100
define lan-nets = { 172.16.100.0/24 , 172.17.100.0/24 }
table inet filter {
       chain input {
               type filter hook input priority filter; policy drop;
               ct state established,related counter accept
               ct state new iif "lo" counter accept
               ct state new tcp dport $local_tcp_ports counter accept
               ct state new iif $save_interfaces counter accept
               log prefix "--nftables-drop-input--"
       }

       chain forward {
               type filter hook forward priority filter; policy drop;
               ct state established,related counter accept
               ct state new iif $save_interfaces counter accept
               log prefix "--nftables-drop-forward--"
               }
       chain output {
               type filter hook output priority filter; policy drop;
               ct state established,related counter accept
               ct state new counter accept
               log prefix "--nftables-drop-output--"
       }

}
table inet nat {
   chain postrouting {
       type nat hook postrouting priority srcnat; policy accept;
       oif $wandev ip saddr $lan-nets counter snat ip to $wanip
    }
}

Frage

  • Wieso geht ein ssh server aber kein ssh ns?


#!/usr/sbin/nft -f
flush ruleset
define local_tcp_ports = { 22 }
define save_interfaces = { enp0s8, enp0s9, enp0s10 }
define wandev = enp0s3
define wanip = 192.168.6.100
define ns    = 10.88.100.21
define ns-tcp-ports = { 22, 53 }
define ns-udp-ports = {  53 }
define dmzdev = enp0s8

define lan-nets = { 172.16.100.0/24 , 172.17.100.0/24 }
table inet filter {
      chain input {
              type filter hook input priority filter; policy drop;
              ct state established,related counter accept
              ct state new iif "lo" counter accept
              ct state new tcp dport $local_tcp_ports counter accept
              ct state new iif $save_interfaces counter accept
              log prefix "--nftables-drop-input--"
      }

      chain forward {
              type filter hook forward priority filter; policy drop;
              ct state established,related counter accept
              ct state new iif $save_interfaces counter accept
              ct state new iif $wandev oif $dmzdev ip  daddr $ns tcp dport $ns-tcp-ports counter accept
              ct state new iif $wandev oif $dmzdev ip  daddr $ns udp dport $ns-udp-ports counter accept
              ct state new iif $wandev oif $dmzdev ip  daddr $ns icmp type echo-request counter accept
              log prefix "--nftables-drop-forward--"
              }
      chain output {
              type filter hook output priority filter; policy drop;
              ct state established,related counter accept
              ct state new counter accept
              log prefix "--nftables-drop-output--"
      }

}
table inet nat {
  chain postrouting {
      type nat hook postrouting priority srcnat; policy accept;
      oif $wandev ip saddr $lan-nets counter snat ip to $wanip
   }
}

Aufgaben

  • Installieren sie einen debian Rechner in der dmz
  • Er sollte die IP 10.88.X.33/24
  • Der Name sollte debian.itX.int lauten
  • Die restlichen Daten sollten bekannt sein.
  • Installieren sie hier folgende Pakete
  • apache2 dovecot-imap postfix
  • Welche ipv4 Ports sind nun geöffnet?
  • Schalten sie diese frei.
  • Testen sie mit nmap. (Wenn icmp abgeschaltet ist bitte Option -Pn nutzen)
Abgerufen von „http://wiki.ixheim.de/index.php?title=Nftables_Firewall_Basis_Konfiguration&oldid=42585“