追踪路由的小程序程序原理：程序发送一个请求回显类型为8的icmp包，开始设置此包ttl为1，到达第一个路由器时，路由器会将ttl减1，此时ttl变为0，

// 路由器即会丢弃此包，并发送一个超时类型为11的icmp包，程序接收此包，解析出此包的源ip，即为第一个路由器的ip,依次类推，

// 发第二个请求回显icmp包，ttl设置为2，第二个路由器也会像上面第一个一样处理此包，即可获得第二个路由器的ip, 这样不断的

// 增加icmp包ttl值，当ttl足够大，icmp包可以到达目的地时，

// 目的地会发送一个回应应答报文或者是目的地不可达报文，此时路由跟踪即完成-Trace the routing of the applet program Principle: The program sends a request echo type 8 icmp packet, began to set this packet ttl to 1, to reach the first router, the router will ttl minus 1, then ttl becomes 0,

// router will discard this packet and send a timeout type icmp package 11, the program receives this package, parse out the source of this package ip, is the first router ip, and so on,

// send a second request echo icmp package, ttl is set to 2, the second router will be the same as the first one to deal with this package, you can get the second router ip, so the constant

//Increase icmp packet ttl value, when ttl large enough, icmp package can reach the destination,

// The destination sends a reply-reply message or a destination-unreachable packet, and the route tracing is completed.