Firewall-Nat-Linux - Netzwerk und Serveradministration

Erklärung

• XX = Platznummer
• Y = Klassensaal

Hostname

• hostnamectl set-hostname fw.it2XX.int

Interfaces

• cat /etc/network/interfaces

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
#WAN
auto enp0s3
iface enp0s3 inet static
 address 192.168.9.2XX/24
 gateway 192.168.9.254
 post-up ip route add 10.88.0.0/16 via 192.168.Y.88
 post-up /usr/local/sbin/nat.sh

#LAN
auto enp0s8
iface enp0s8 inet static
 address 172.16.2XX.1/24

#DMZ
auto enp0s9
iface enp0s9 inet static
 address 10.88.2XX.1/24

#SERVERS
auto enp0s10
iface enp0s10 inet static
 address 10.2XX.1.1/24

Hosts

• cat /etc/hosts

127.0.0.1        localhost
127.0.1.1        fw.it2XX.int fw

# The following lines are desirable for IPv6 capable hosts
::1      localhost ip6-localhost ip6-loopback
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

Resolver

• cat /etc/resolv.conf

search it2XX.int
nameserver 192.168.Y.88

Nat

• cat /usr/local/sbin/nat.sh

#!/bin/bash
LAN="172.16.2XX.0/24"
SERVERS="10.2XX.1.0/24"
DMZ="10.88.2XX.0/24"
#Nat Regeln flushen
iptables -t nat -F 
#Nat Regelen setzen
iptables -t nat -A POSTROUTING -s $DMZ -d 192.168.Y.0/24 -j RETURN
iptables -t nat -A POSTROUTING -s $DMZ -d 10.88.0.0/16 -j RETURN
iptables -t nat -A POSTROUTING -s $DMZ -o enp0s3 -j MASQUERADE
iptables -t nat -A POSTROUTING -s $LAN -o enp0s3 -j MASQUERADE
iptables -t nat -A POSTROUTING -s $SERVERS -o enp0s3 -j MASQUERADE

• chmod +x /usr/local/sbin/nat.sh

NAT mit nftables

#!/usr/sbin/nft -f

# Variablen
define LAN = 172.16.2XX.0/24
define SERVERS = 10.2XX.1.0/24
define DMZ = 10.88.2XX.0/24

# Alte Regeln löschen (flush)
flush table ip nat

# NAT-Tabelle erstellen/verwenden
table ip nat {
    chain postrouting {
        type nat hook postrouting priority 100; policy accept;
        
        # DMZ nach 192.168.Y.0/24 - kein NAT (RETURN)
        ip saddr $DMZ ip daddr 192.168.Y.0/24 return
        
        # DMZ nach 10.88.0.0/16 - kein NAT (RETURN)
        ip saddr $DMZ ip daddr 10.88.0.0/16 return
        
        # DMZ nach außen (enp0s3) - Masquerade
        ip saddr $DMZ oif enp0s3 masquerade
        
        # LAN nach außen - Masquerade
        ip saddr $LAN oif enp0s3 masquerade
        
        # SERVERS nach außen - Masquerade
        ip saddr $SERVERS oif enp0s3 masquerade
    }
}

Forward

• echo "net.ipv4.ip_forward=1" >> /etc/sysctl.conf
• sysctl -p

Reboot

• systemctl reboot