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 * [http://linux-ip.net/ Guide to IP Layer Network Administration with Linux (http://linux-ip.net/)]
 * [http://www.linux.or.jp/JF/JFdocs/Adv-Routing-HOWTO/lartc.kernel.obscure.html Linux Advanced Routing & Traffic Control HOWTO - あまり知られていない設定]

 = disable ipv6 =
 * 以下の一行を、modprobeの設定ファイルに追加
{{{
install ipv6 /sbin/modprobe -n -i ipv6
}}}
   * Ubuntu -> /etc/modprobe.d/blacklist (/etc/modprobe.d/* のどれでも可)
   * RedHat -> /etc/modprobe.conf

 * [http://d.hatena.ne.jp/adsaria/20080525 UbuntuでIPv6を無効化 - adsaria mood]
 * [http://fun.poosan.net/sawa/index.php?UID=1197817541 Fedora で IPv6 をスマートに無効化]

 = open relay test =
 * telnet localhost 25 「以外」のIPで繋いで、以下のような例でメール送信できたらOpen relayになっているので注意
{{{
HELO mitty.jp
MAIL FROM: hoge@mitty.jp
RCPT TO: fuga@example.org
DATA
From: hoge@mitty.jp
Subject: test
relay testmail
.
QUIT
}}}

 = warning with dhcp3 =
 * [https://bugs.launchpad.net/ubuntu/+source/dhcp3/+bug/39249 Bug #39249 in dhcp3 (Ubuntu): “(Dapper, Hardy) can't create /var/lib/dhcp3/dhclient.eth0.leases: Permission denied”]
   * ◦sudo chown dhcp:dhcp /var/lib/dhcp3/

 = /etc/ppp/ip-up.local =
 * Ubuntu(Debian)の、/etc/network/interfacesにおけるpost-up command(のPPP版)にあたるもの
 * [http://tsutomu.lasttom.jp/item/30 らpapa's Web Site - CentOSでソースポリシールーティング]
 * [http://www.org3.net/tech_notes/flets-square.html フレッツ・スクウェア - マルチセッション]

 = SYN Cookies =
 * [http://ja.wikipedia.org/wiki/SYN_cookies SYN cookies - Wikipedia]
 * [http://lkml.org/lkml/2008/2/5/167 LKML: Andi Kleen: Re: [PATCH] Add IPv6 support to TCP SYN cookies]
 * [http://www.soi.wide.ad.jp/class/20060020/slides/11/26.html SYN Cookiesの動作]

 * to enable
   * sysctl -w net.ipv4.tcp_syncookies=1
   * /etc/sysctl.conf > net.ipv4.tcp_syncookies=1

 = calculate netmask =
 * ipcount <= perlのNet::IPモジュールに含まれる
   * aptitude install libnet-ip-perl
     * /usr/share/doc/libnet-ip-perl/examples/ipcount
{{{
Usage:
        ipcount [-r] [-d <prefix>] address

        -r: Print Reverse Ranges
        -d <prefix>: Cut down the original prefix in several prefixes

The address range can be one of:

ipcount IP + size
ipcount IP1 - IP2
ipcount IP/len
}}}
 * via [http://linux.mini13i.gotdns.org/?tool%2Fnetmask%B7%D7%BB%BB tool/netmask計算 - Linux Tips]

 = NICが活性化される順序 = #NIClinkOrder
 * CentOS
   * ifcfg? の数字が若い順に固定？(任意の順序に変更できるか不明)
 * Ubuntu
   * interfacesに記載された順の模様

 = wakeonlan =
 * sudo aptitude install -R wakeonlan
 * デフォルトルートとは違うNICから送出したい場合
   * wakeonlan -i 192.168.100.255 00:1D:60:XX:YY:ZZ
{{{
Sending magic packet to 192.168.100.255:9 with 00:1D:60:XX:YY:ZZ
}}}
   * tcpdump -np port 9 -i eth0
{{{
11:30:32.420790 IP 192.168.100.254.34625 > 192.168.100.255.9: UDP, length 102
}}}

 = fix DNS server on DHCP network =
 * DHCP配下のネットワークで、DNSを固定する
   * デフォルトではIP割り当て時に/etc/resolve.confが自動で書き換わってしまう
 * man dhclient.conf
{{{
OPTION MODIFIERS
       The supersede statement

        supersede [ option declaration ] ;

       If for some option the client should always use a locally-configured value or values rather than whatever is supplied by the  server,  these  values  can  be
       defined in the supersede statement.
}}}
 * /etc/dhcp3/dhclient.conf
{{{
supersede domain-name-servers 127.0.0.1;
}}}
   * => /etc/resolv.conf
{{{
nameserver 127.0.0.1
}}}