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使用 nc 命令无法看到 udp 数据包，使用 tcpdump 即可

tag-icon • tag-icon ip udp tcpdump netcat alpine
使用 nc 命令无法看到 udp 数据包，使用 tcpdump 即可

我尝试使用nc( netcat) 命令捕获 UDP 数据，但未输出任何内容。我需要向命令传递哪些选项/参数才能nc获取输出？

tcpdump确实显示了 UDP 数据。我尝试的原因nc是，当我知道如何捕获时，我可以在另一个最终需要监听传入数据的程序中使用这些设置。

我尝试过的事情nc有：

$ nc -ul 8002
$ nc -ulb 8002
$ nc -u -l -s 192.168.2.235 -p 8002
$ nc -u -l -s 192.168.2.255 -p 8002
$ nc -u -l -b -s 192.168.2.235 -p 8002
$ nc -u -l -b -s 192.168.2.255 -p 8002
$ nc -u -l -b -s 255.255.255.255 -p 8002
$ nc -u -l -s 192.168.2.235 8002
$ nc -u -l -s 192.168.2.255 8002
$ nc -u -l -s 255.255.255.255 8002

全部均无输出。

工作tcpdump命令：

$ sudo tcpdump -A -i eth1 'udp port 8002'
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on eth1, link-type EN10MB (Ethernet), snapshot length 262144 bytes
12:42:32.823653 IP 192.168.1.52.5678 > 255.255.255.255.8002: UDP, length 23
[email protected]....$RADPT,5.5,0.0,40,*57

12:42:32.987098 IP 192.168.1.53.5678 > 255.255.255.255.8002: UDP, length 24
E..4~(..@.:....5.......B. ..$RBDPT,0.04,0.0,40,*60

我的网络配置：

$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether 4c:02:89:17:be:de brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.2/24 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::4e02:89ff:fe17:bede/64 scope link
       valid_lft forever preferred_lft forever
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether 4c:02:89:17:be:df brd ff:ff:ff:ff:ff:ff
    inet 192.168.2.235/24 scope global eth1
       valid_lft forever preferred_lft forever
    inet6 fe80::4e02:89ff:fe17:bedf/64 scope link
       valid_lft forever preferred_lft forever
4: eth2: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
    link/ether 4c:02:89:17:be:e0 brd ff:ff:ff:ff:ff:ff
5: eth3: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
    link/ether 4c:02:89:17:be:e1 brd ff:ff:ff:ff:ff:ff
6: eth4: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
    link/ether 4c:02:89:17:be:dd brd ff:ff:ff:ff:ff:ff
8: docker0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default
    link/ether 02:42:22:77:fb:27 brd ff:ff:ff:ff:ff:ff
    inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0
       valid_lft forever preferred_lft forever
    inet6 fe80::42:22ff:fe77:fb27/64 scope link
       valid_lft forever preferred_lft forever
9: slcan0: <NOARP,UP,LOWER_UP> mtu 16 qdisc pfifo_fast state UNKNOWN group default qlen 10
    link/can
12: wg0: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1420 qdisc noqueue state UNKNOWN group default qlen 1000
    link/none
    inet 10.24.1.3/16 scope global wg0
       valid_lft forever preferred_lft forever

数据是在 eth1 上接收的，我无法更改 eth0 的 ip/网络掩码，因为这样我会失去与计算机的连接（一切都在远程运行）。操作系统是 Linux Alpine。

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