> For the complete documentation index, see [llms.txt](https://book.bsdcn.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://book.bsdcn.org/man/man4/lo.4.md).

# lo.4

`lo` — 软件环回网络接口

## 名称

`lo`

## 概要

`device loop`

## 描述

`loop` 接口是一种软件环回机制，可用于性能分析、软件测试和/或本地通信。与其他网络接口一样，环回接口必须为每个要使用的地址族分配网络地址。这些地址可通过相应地址族的适当 ioctl(2) 命令设置。环回接口应最后配置，因为协议可能将配置顺序作为优先级的指示。除非不存在硬件接口，否则环回接口*绝不*应首先配置。

如果在环回接口上启用了发送校验和卸载功能，IP、UDP、TCP 或 SCTP 不会为在该接口上发送的数据包生成校验和。默认情况下，此功能处于启用状态，以避免在数据损坏可能性较低的本地通信中产生校验和开销。

如果在环回接口上禁用了接收校验和卸载功能，则先前设置的指示有效校验和的标志将被清除。默认情况下，此功能处于启用状态，以避免在已验证后再次进行校验和验证。

## 诊断

* lo%d: can't handle af%d。接口收到一个地址格式不适用于当前地址族的消息；该数据包被丢弃。

## 参见

[inet(4)](/man/man4/inet.4.md), [intro(4)](/man/man4/intro.4.md)

## 历史

`loop` 设备出现于 4.2BSD。当前的校验和生成与验证回避策略出现于 FreeBSD 8.0。


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