NTP工作模式
我是 NTP 协议的新手。我阅读了 RFC1305，并对 NTP 有一些疑问。 我的问题与 NTP 工作模式有关。 根据 RFC1305 有 8 种模式
| 0 |保留
| 1 |对称主动
| 2 |对称被动
| 3 |客户
| 4 |服务器
| 5 |广播
| 6 | NTP控制消息
| 7 |保留供私人使用
我的问题：
1- 对称无源设备和对称有源设备之间有什么区别？
2- 两个对称主动设备可以相互同步，两个被动主动设备也可以相互同步，但是对称被动设备是否可以由对称主动设备同步，反之亦然？
3- 当对称被动设备连接到对称主动设备时，哪一个首先发送 NTP 数据包？
4- 广播模式下会发生什么？客户端是否发送任何 NTP 数据包，还是只有广播者发送？
5-”为了同步一些具有 CLASS D IP 的客户端，服务器填充 3 个时间戳字段（接收时间戳为空）并将模式设置为 5 并将数据包发送到 224.0.1.1，客户端得到该信息数据包，并且他们在此过程中什么也不发送”这是真的吗？
6- 谁发送 NTP 控制消息？客户还是广播公司？这是做什么用的？它的正确答案是什么？它总是 12 字节长吗？
7-“第 1 层 NTP 服务器（已连接 GPS）的行为如下：模式 1 用模式 2 应答，模式 3 用模式 4 应答，模式 6 用 7 应答”这是真的吗？
I am new to NTP protocol. I read the RFC1305 and have some questions about NTP.
My questions are related to NTP working modes.
According to RFC1305 there are 8 modes
| 0 | reserved
| 1 | symmetric active
| 2 | symmetric passive
| 3 | client
| 4 | server
| 5 | broadcast
| 6 | NTP control message
| 7 | reserved for private use
My questions:
1- What are the differences between the symmetric passive device and symmetric active one?
2- Two symmetric active device can sync each other and Two passive active device can sync each other too ,but Can a symmetric passive device been synced by a symmetric active one and vice versa?
3- When a Symmetric passive device is connected to symmetric active one which one sends the NTP packet first?
4- What happens in broadcasting mode? Does the client send any NTP packet or only the broadcaster does that?
5- ”in order to sync some clients who have CLASS D IP ‘s , the server fills the 3 time stamp fields(receive time stamp is null) and set the mode to 5 and send the packet to 224.0.1.1 and clients get that packet and they send nothing in this procedure” Is this true?
6- Who sends the NTP control message? Client or broadcaster? What’s it for? What’s the appropriate answer for it?is it always 12 bytes long?
7- “A stratum 1 NTP server (GPS connected) acts like this: answer mode 1 requests with mode 2, mode 3 with mode 4 and mode 6 with 7” Is this true?
如果你对这篇内容有疑问，欢迎到本站社区发帖提问 参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。
绑定邮箱获取回复消息
由于您还没有绑定你的真实邮箱，如果其他用户或者作者回复了您的评论，将不能在第一时间通知您！
发布评论
评论（2）
只能回答几个问题：
-4。在此模式下，仅允许服务器（广播者）发送任何 ntp 数据包
客户端仅侦听接口，解析接收到的数据包并相应地设置其时钟 - 没有发送回复。
但客户端也可能发送 ntp 请求，服务器不应回复此请求。
-5。正确的。该客户没有应发送的答复。
can only reply to a few questions:
-4. only the server (broadcaster) is allowed to send any ntp-packet in this mode
clients only listen to the interface, parse the received packet and set their clock accordingly - there is no reply being send.
but clients may send a ntp-request too, the server should then not reply to this one.
-5. right. there is no answer supposed to be send by this clients.
模式6由ntpq程序使用。例如，它可以查询“服务器已知的对等点列表以及它们的状态摘要”（来自手册页）。
最近有人利用这一点进行DDOS反射攻击，因为它可以用欺骗的IP地址触发，并且回复大于查询。 1
因此，应阻止模式 6 和 7 查询外部来源。
Mode 6 is used by the ntpq program. It can for example query "a list of the peers known to the server as well as a summary of their state" (from the man page).
This has recently be exploited to do DDOS reflection attacks, because it can be triggered with spoofed IP address, and the reply is larger than the query. 1
For this reason mode 6 and 7 queries should be blocked from outside sources.