Dynamic NAT動態 NAT

While static NAT provides a permanent mapping between a single local and a single global address, dynamic NAT maps multiple local to multiple global addresses. Therefore, you must define two sets of addresses: the set of local addresses and the set of global addresses. The sets usually do not have the same size. Since the set of global addresses usually contains public IPv4 addresses, it is smaller than the set of local addresses.

靜態 NAT 提供單一本地位址與單一全域位址之間的永久對映，動態 NAT 則是將多個本地位址對映到多個全域位址。因此，你必須定義兩組位址：本地位址集合與全域位址集合。這兩組位址的數量通常不相同。由於全域位址集合通常包含的是公有 IPv4 位址，因此其規模通常小於本地位址集合。

In Cisco IOS Software terminology, a group of addresses is called a pool of addresses. Address pools are named and are referenced by their name in commands and command outputs. IP addresses that belong to a pool are specified using a reference IP address and a subnet mask or prefix length.

在 Cisco IOS 軟體術語中，一組位址稱為位址集區（pool）。位址集區會有名稱，並在指令與指令輸出中以其名稱作為參照。屬於某個集區的 IP 位址，是以一個參考 IP 位址搭配子網路遮罩或前綴長度來指定的。

Dynamic NAT takes global addresses from a pool on a first-come, first-served basis. Each connection initiated from the inside will use one of the addresses from the pool of global addresses. Once the global pool is exhausted, new connections will not be translated and the communication with the outside networks will not be possible. Although the global pool is smaller, it usually suffices, since local devices do not connect to the outside at the same moment. Nevertheless, you should make sure to provide enough global addresses to satisfy the need for outbound communications.

動態 NAT 會以先到先得的方式從集區中取用全域位址。每個由內部發起的連線都會使用全域位址集區中的其中一個位址。一旦全域集區用盡，新的連線就無法被轉譯，也就無法與外部網路通訊。雖然全域集區的規模較小，但通常已經足夠，因為本地裝置不會同時連線到外部。儘管如此，你仍應確保有足夠的全域位址可滿足出向通訊的需求。