NAT Fundamentals

このページで学ぶこと

• NAT Inside Local
• NAT Inside Global
• NAT Outside Local
• NAT Outside Global
• NAT Address Terminology
• NAT Inside Interface Role
• NAT Outside Interface Role
• NAT Inside Source Flow
• NAT Local Global Versus Private Public
• NAT Outside Address Typical Equality

NATの4 Address

Inside Host 10.10.10.10
↓ Inside Local
NAT Router
↓ Inside Global 203.0.113.10
Outside Network 198.51.100.20

Inside Source NATだけなら典型的に
Outside Local  = 198.51.100.20
Outside Global = 198.51.100.20

Inside / OutsideはNATの位置関係、Local / Globalはどちら側から見たAddressかを表します。Private / Publicの単純な別名ではありません。

Interface Role

interface GigabitEthernet0/0
 ip nat inside

interface GigabitEthernet0/1
 ip nat outside

ip nat inside / ip nat outsideはNAT処理上のInterface Roleを定義します。

Packetの見方

Inside Local 10.10.10.10
↓ Source Translation
Inside Global 203.0.113.10
↓
Outside Host 198.51.100.20

Inside Source NATでは主にInside HostのSource Addressを外部向けAddressへ変換します。

重要な注意点

• Inside Local ≠ Inside Global
• Outside Local ≠ Outside Global
• Local / Global ≠ Private / Publicの単純な別名
• Inside / Outside = NAT Interface Role
• Inside Source NATではOutside Local = Outside Globalとなることが多いが、普遍的規則ではない