网络工程 - TTl !=1 ICMP Port Unreachable 消息中的值 (traceroute) - 吾爱随笔录

我认为当一个跃点（包括目标跃点）回复一个 UDP 请求（通过 traceroute）时，总是有 ttl=1 如此链接

但我在来自目标跃点的 ICMP Port Unreachable 消息响应中看到 ttl 不等于 1。像这样

8.8.8.8 > 192.168.1.6: ICMP 8.8.8.8 udp port 33466 unreachable, length 36
    IP (tos 0x80, ttl 2, id 10956, offset 0, flags [none], proto UDP (17), length 60, bad cksum 8d66 (->bba7)!)
    192.168.1.6.33995 > 8.8.8.8.33466: UDP, length 32
19:03:42.346002 IP (tos 0x0, ttl 46, id 0, offset 0, flags [none], proto ICMP (1), length 56)
    8.8.8.8 > 192.168.1.6: ICMP 8.8.8.8 udp port 33467 unreachable, length 36
    IP (tos 0x80, ttl 3, id 10957, offset 0, flags [none], proto UDP (17), length 60, bad cksum 8c65 (->baa6)!)
    192.168.1.6.49358 > 8.8.8.8.33467: UDP, length 32
19:03:42.348871 IP (tos 0x0, ttl 46, id 0, offset 0, flags [none], proto ICMP (1), length 56)
    8.8.8.8 > 192.168.1.6: ICMP 8.8.8.8 udp port 33468 unreachable, length 36
    IP (tos 0x80, ttl 2, id 10959, offset 0, flags [none], proto UDP (17), length 60, bad cksum 8d63 (->bba4)!)
    192.168.1.6.44693 > 8.8.8.8.33468: UDP, length 32
19:03:42.362155 IP (tos 0x0, ttl 46, id 0, offset 0, flags [none], proto ICMP (1), length 56)
    8.8.8.8 > 192.168.1.6: ICMP 8.8.8.8 udp port 33469 unreachable, length 36
    IP (tos 0x80, ttl 2, id 10962, offset 0, flags [none], proto UDP (17), length 60, bad cksum 8d60 (->bba1)!)
    192.168.1.6.43577 > 8.8.8.8.33469: UDP, length 32
19:03:42.362185 IP (tos 0x20, ttl 47, id 0, offset 0, flags [none], proto ICMP (1), length 56)
    8.8.8.8 > 192.168.1.6: ICMP 8.8.8.8 udp port 33470 unreachable, length 36
    IP (tos 0x80, ttl 3, id 10963, offset 0, flags [none], proto UDP (17), length 60, bad cksum 8c5f (->baa0)!)
    192.168.1.6.60249 > 8.8.8.8.33470: UDP, length 32
19:03:42.382381 IP (tos 0x0, ttl 46, id 0, offset 0, flags [none], proto ICMP (1), length 56)
    8.8.8.8 > 192.168.1.6: ICMP 8.8.8.8 udp port 33471 unreachable, length 36
    IP (tos 0x80, ttl 3, id 10965, offset 0, flags [none], proto UDP (17), length 60, bad cksum 8c5d (->ba9e)!)
    192.168.1.6.33430 > 8.8.8.8.33471: UDP, length 32

你能解释一下为什么会这样吗？

谢谢阅读！