DHCP

DHCP（动态主机配置协议）¶

DHCP 的工作流程通常分为以下四个步骤（简称 DORA）： The DHCP process typically involves the following four steps, abbreviated as DORA:

DHCP Process

Discover（发现）:
当一个设备（例如电脑、手机等）首次连接到网络时，它会发送一个 DHCP Discover 报文，广播给网络中的所有设备，询问是否有 DHCP 服务器能够提供网络配置。 When a device (e.g., computer, smartphone) first connects to a network, it sends a DHCP Discover message, broadcasted to all devices on the network, asking if any DHCP server can provide network configuration.
Offer（提供）:
DHCP 服务器接收到 Discover 报文后，会回复一个 DHCP Offer 报文，提供一个可用的 IP 地址及其他网络配置信息。

Upon receiving the Discover message, the DHCP server replies with a DHCP Offer message, providing an available IP address and other network configuration details.
Request（请求）:
设备选择一个 DHCP 服务器提供的 IP 地址后，向该服务器发送一个 DHCP Request 报文，确认它将使用这个 IP 地址。

The device selects the offered IP address and sends a DHCP Request message to the server, confirming its intention to use that IP address.
Acknowledge（确认）:
最后，DHCP 服务器发送一个 DHCP Acknowledge 报文，确认设备的 IP 地址和配置，设备此时正式获得网络连接。

Finally, the DHCP server sends a DHCP Acknowledge message, confirming the device's IP address and configuration, at which point the device is fully connected to the network.

自动 IP 地址分配 (Automatic IP Address Assignment):
DHCP 自动为网络中的设备分配 IP 地址，确保 IP 地址不冲突，并且有效利用 IP 地址资源。

DHCP automatically assigns IP addresses to devices on the network, ensuring no IP conflicts and efficient use of IP resources.
减少手动配置错误 (Reduction of Manual Configuration Errors):
由于 DHCP 自动化配置过程，减少了手动配置时可能出现的错误，如 IP 地址冲突或错误的网络参数。

The automated process of DHCP reduces the likelihood of errors in manual configuration, such as IP address conflicts or incorrect network parameters.
IP 地址租约管理 (IP Address Lease Management):
DHCP 使用租约机制分配 IP 地址，设备只在租约期间拥有该 IP 地址。租约到期后，IP 地址可以被重新分配给其他设备。

DHCP uses a lease mechanism to allocate IP addresses, where a device only owns the IP address for the duration of the lease. After the lease expires, the IP address can be reassigned to another device.
动态网络配置 (Dynamic Network Configuration):
允许设备在移动到不同的网络时，自动获取新的网络配置，而不需要手动调整设置。

Allows devices to automatically obtain new network configurations when moving to different networks without the need for manual adjustment.

UDP 67: 服务器端端口，用于 DHCP Discover 和 DHCP Request 报文。
- Server-side port used for DHCP Discover and DHCP Request messages.
UDP 68: 客户端端口，用于接收 DHCP Offer 和 DHCP Acknowledge 报文。
- Client-side port used for receiving DHCP Offer and DHCP Acknowledge messages.

动态分配 (Dynamic Allocation):
DHCP 服务器自动从 IP 地址池中分配一个 IP 地址，设备在租约期间使用该地址，租约到期后，IP 地址可能会被回收并重新分配。
- The DHCP server automatically allocates an IP address from a pool, which the device uses during the lease period. Once the lease expires, the IP address can be recycled and reallocated.
自动分配 (Automatic Allocation):
类似于动态分配，但 DHCP 服务器会记录已分配的 IP 地址，并尽量为同一设备分配相同的 IP 地址。
- Similar to dynamic allocation, but the DHCP server remembers the previously assigned IP addresses and attempts to assign the same IP to the same device whenever possible.
手动分配 (Manual Allocation):
由管理员手动预先将设备的 MAC 地址与 IP 地址绑定，DHCP 服务器根据设备的 MAC 地址分配固定的 IP 地址。
- The administrator manually binds the device's MAC address to a specific IP address, and the DHCP server allocates that IP address to the device based on its MAC address.

简化网络管理 (Simplified Network Management):
DHCP 自动化分配 IP 地址和其他网络配置，大大简化了网络管理任务，尤其是在有大量设备的网络环境中。
- DHCP automates the allocation of IP addresses and other network configurations, significantly simplifying network management tasks, especially in environments with a large number of devices.
提高灵活性 (Increased Flexibility):
DHCP 允许设备轻松地在不同网络中移动，而不需要手动重新配置网络设置。
- DHCP allows devices to easily move between different networks without the need for manual reconfiguration.
减少 IP 地址冲突 (Reduction of IP Address Conflicts):
DHCP 确保每个设备获得唯一的 IP 地址，避免了手动配置可能导致的 IP 地址冲突问题。
- DHCP ensures that each device receives a unique IP address, avoiding IP address conflicts that can arise from manual configuration.

安全性 (Security):
DHCP 服务器可以通过广播方式发送 IP 地址配置，这意味着未经授权的设备也可能获得 IP 地址。为此，可以使用 DHCP Snooping 等技术来增加安全性。
- DHCP servers broadcast IP address configurations, meaning unauthorized devices could potentially obtain IP addresses. Techniques such as DHCP Snooping can be used to enhance security.
租约管理 (Lease Management):
在网络中可能会遇到租约到期后无法及时续约或冲突的情况，需合理配置租约时间和地址池大小。
- In a network, you may encounter situations where leases expire without timely renewal or conflicts occur. Proper lease time and address pool size configurations are necessary.
依赖性 (Dependence):
网络设备严重依赖 DHCP 服务器。如果 DHCP 服务器出现故障，网络中的设备可能无法获得 IP 地址，从而无法连接网络。
- Network devices heavily depend on the DHCP server. If the DHCP server fails, devices on the network may not obtain IP addresses and, consequently, cannot connect to the network.