• kernelの再構築
• ipchainsのインストール

1. kernelの設定
   2.2.6での設定です。PPPを使う場合はNetwork device supportでPPPを[M]にします。

   <*> Packet socket
   [*] Kernel/User netlink socket
   [*] Routing messages
   <*> Netlink device emulation
   [*] Network firewalls
   [*] Socket Filtering
   <*> Unix domain sockets
   [*] TCP/IP networking
   [ ] IP: multicasting
   [*] IP: advanced router
   [*] IP: policy routing
   [ ] IP: equal cost multipath
   [ ] IP: use TOS value as routing key
   [ ] IP: verbose route monitoring
   [*] IP: large routing tables
   [*] IP: fast network address translation
   [*] IP: kernel level autoconfiguration
   [ ]       BOOTP support
   [ ]       RARP support
   [*] IP: firewalling
   [*] IP: firewall packet netlink device
   [*] IP: always defragment (required for masquerading)
   [*] IP: use FWMARK value as routing key
   [*] IP: transparent proxy support
   [*] IP: masquerading
   --- Protocol-specific masquerading support will be built as modules.
   [*] IP: ICMP masquerading
   --- Protocol-specific masquerading support will be built as modules.
   [*] IP: masquerading special modules support
    IP: ipautofw masq support (EXPERIMENTAL)
    IP: ipportfw masq support (EXPERIMENTAL)
    IP: ip fwmark masq-forwarding support (EXPERIMENTAL)
   [*] IP: optimize as router not host
   < > IP: tunneling
   < > IP: GRE tunnels over IP
   [*] IP: aliasing support
   [*] IP: ARP daemon support (EXPERIMENTAL)
   [*] IP: TCP syncookie support (not enabled per default)                  
   

2. /etc/conf.modulesに追加

   /etc/conf.modules

   alias net-pf-4 off
   alias net-pf-5 off
   
   alias ppp-compress-24 off
   alias ppp-compress-26 off
   

3. /etc/rc.d/rc.modulesに追加

   /etc/rc.d/rc.modules

   /sbin/modprobe ip_masq_ftp.o
   /sbin/modprobe ip_masq_raudio.o
   /sbin/modprobe ip_masq_irc.o
   /sbin/modprobe ip_masq_cuseeme.o
   /sbin/modprobe ip_masq_vdolive.o
   
   

1. ipchainsをインストール
   IP firewall の設定をするためにipchainsをインストールします。
   kernel2.0ではipfwadmを使用しましたが、2.1以降はipchainsで設定する事になります。 kernel2.0 + ipfwadmですでに動作させているという場合はipchainsのDocumentにコマンド対応表がついていますので、苦労無く乗り換えられると思います。
2. とりあえず ./configure ; make ; make install
3. IPCHAINS-HOWTO を熟読する。
4. 5.1 Masquerading/forwarding doesn't work!書いてある通り、
   /proc/sys/net/ipv4/ip_forward を1にするコマンドをrc.localに追加する

   /etc/rc.d/rc.local

   #
   # enable IP Fowarding
   #
   if [ -e /proc/sys/net/ipv4/ip_forward ]; then
           echo -n "Setting up IP forwarding..."
           echo 1 > /proc/sys/net/ipv4/ip_forward
           echo "done."
   fi