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如何在Java中获取UDP数据包的TTL？

[英]How to get TTL of a UDP packet in Java?

原文 2010-11-25 14:12:58 4 3 java/ android/ udp/ ttl

I am using a Java application to send UDP packets to an Android device. 我正在使用Java应用程序将UDP数据包发送到Android设备。 There I have another Java application that receives these UDP packets and displays its data - very simple. 我有另一个Java应用程序接收这些UDP数据包并显示其数据 - 非常简单。

Now I am working on some routing algorithms - therefore it would be nice to know how many hops a UDP packet did since it was send. 现在我正在研究一些路由算法 - 因此，知道UDP数据包自发送以来的跳数有多好。 My idea is to just read out the TTL (time-to-live) value of the packet and display it. 我的想法是只读出数据包的TTL（生存时间）值并显示它。 Do you know if this is possible with pure Java? 你知道纯Java是否可行吗？ The class DatagramPacket doesn't give any hints at all. DatagramPacket类根本不提供任何提示。

I guess that this is not possible because this information might already have been removed at a lower layer, but I just want to be sure. 我想这是不可能的，因为这些信息可能已经在较低层删除了，但我只想确定。 :-) :-)

3 个解决方案

The TTL field is, as you know, a feature of the underlying IP protocol (when used), not of UDP. 如您所知， TTL字段是底层IP协议（使用时）的一个特性，而不是UDP的特性。 So it makes sense for it not to be visible in the DatagramPacket API. 因此，它在DatagramPacket API中不可见是有意义的。 However, I think you're right; 但是，我认为你是对的; it's not normally possible to get access to the IP packets through datagram-level API:s. 通常不可能通过数据报级API访问IP数据包：s。 You probably need to look into packet capture. 您可能需要查看数据包捕获。

This is part of IP header and is set from socket, apparently only for multicast sockets. 这是IP头的一部分，是从套接字设置的，显然只适用于多播套接字。 Check this answer: 检查这个答案：

Java control IP TTL? Java控制IP TTL？

For your purpose, if I get it correctly, it would be sufficient to manipulate the TTL of the sender; 为了您的目的，如果我正确地理解，那么操纵发送者的TTL就足够了; eg set TTL of the sending socket to 1,2,3,4,5 and for each send one message with content "1","2","3","4" or "5" etc. Some will likely be missing on the receiver... 例如，将发送套接字的TTL设置为1,2,3,4,5，并为每个发送一条内容为“1”，“2”，“3”，“4”或“5”等的消息。有些可能是丢失在接收器上......