February 2024
Beginner to intermediate
304 pages
9h 13m
Japanese
Content preview from 実務で使える メール技術の教科書 基本のしくみからプロトコル・サーバー構築・送信ドメイン認証・添付ファイル・暗号化・セキュリティ対策まで
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1
−
4
—
—
通信相手を識別する
て、それに対して複数のローカル IP アドレスを割り当てることで、IPv4 の IP
アドレスの不足に対応する方法が使われています【図 1-19】。
これにより、インターネット上で相手を識別するために必要なグローバル
IP アドレスの数は減らせますが、利用者・利用端末の数が増え続けることに
変わりはありません。
■ IPv6 の登場
そこで、2 進数で 128 桁の値を用いる IPv6 というバージョンの IP アドレ
スが使われ始めています。1 桁増えると 2 倍になるので、膨大な数の端末を
識別できるようになり、当面は枯渇しないといわれています。
IPv4 では 8 桁ずつ 4 個に分けて 10 進数に変換し、ピリオドで区切って表
現しましたが、IPv6 では 16 桁ずつ 8 個に分けて 16 進数に変換し、コロン
で区切って表現します。
連続する「0」は 1 回に限り省略可能であるなどの違いがありますが、IPv4
のときと変換の考え方は同じです【図 1-20】。
図 1-19
ローカル IP アドレスとグローバル IP アドレスの変換
変換する
ローカル
IPアドレス
グローバル
IPアドレス
グローバル
IPアドレス
192.168.1.4
192.168.1.3
192.168.1.2
192.168.1.1
210.98.76.53210.98.76.54
192.168.1.1
192.168.1.4
192.168.1.3
192.168.1.2
ローカルIPアドレスは
内部で重複しなければ
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.