ping 广播地址时出现问题
当我尝试对 LAN 上的广播地址执行 ping 操作时，每次都仅显示来自 3 个主机的 ICMP 回复，即使有许多主机连接到 LAN。
对于广播地址，我
$ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:1b:38:09:0b:26
inet addr:172.30.120.152 Bcast:172.30.127.255 Mask:255.255.248.0
inet6 addr: fe80::21b:38ff:fe09:b26/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:831096 errors:0 dropped:0 overruns:0 frame:0
TX packets:13022 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:66620362 (66.6 MB) TX bytes:3099025 (3.0 MB)
Interrupt:21 Base address:0x2000
使用了 Bcast addr 172.30.127.255 来 ping 所有人...
$ping -b 172.30.127.255
WARNING: pinging broadcast address
PING 172.30.127.255 (172.30.127.255) 56(84) bytes of data.
64 bytes from 172.30.120.1: icmp_seq=1 ttl=255 time=0.809 ms
64 bytes from 172.30.120.62: icmp_seq=1 ttl=64 time=1.06 ms (DUP!)
64 bytes from 172.30.120.50: icmp_seq=1 ttl=255 time=3.97 ms (DUP!)
64 bytes from 172.30.120.1: icmp_seq=2 ttl=255 time=0.364 ms
64 bytes from 172.30.120.62: icmp_seq=2 ttl=64 time=0.412 ms (DUP!)
64 bytes from 172.30.120.50: icmp_seq=2 ttl=255 time=1.48 ms (DUP!)
64 bytes from 172.30.120.1: icmp_seq=3 ttl=255 time=0.452 ms
64 bytes from 172.30.120.62: icmp_seq=3 ttl=64 time=0.506 ms (DUP!)
64 bytes from 172.30.120.50: icmp_seq=3 ttl=255 time=1.64 ms (DUP!)
为什么只有 3 个主机响应我的 ping。 ifconfig 给出的这个广播地址不是要使用的吗？ 我认为这可能是我无法对 LAN 上的系统进行放大攻击的原因。我用朋友主机的欺骗源地址注入了 ICMP-echo 数据包 并将其发送到这个广播地址，很失望地看到他的带宽没有受到影响...
请解释一下...
When I try to ping the broadcast address on my LAN, it shows ICMP replies from only 3 hosts, everytime, even though there many hosts connected to the LAN.
For the broadcast address, I did
$ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:1b:38:09:0b:26
inet addr:172.30.120.152 Bcast:172.30.127.255 Mask:255.255.248.0
inet6 addr: fe80::21b:38ff:fe09:b26/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:831096 errors:0 dropped:0 overruns:0 frame:0
TX packets:13022 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:66620362 (66.6 MB) TX bytes:3099025 (3.0 MB)
Interrupt:21 Base address:0x2000
I used the Bcast addr 172.30.127.255 to ping everyone...
$ping -b 172.30.127.255
WARNING: pinging broadcast address
PING 172.30.127.255 (172.30.127.255) 56(84) bytes of data.
64 bytes from 172.30.120.1: icmp_seq=1 ttl=255 time=0.809 ms
64 bytes from 172.30.120.62: icmp_seq=1 ttl=64 time=1.06 ms (DUP!)
64 bytes from 172.30.120.50: icmp_seq=1 ttl=255 time=3.97 ms (DUP!)
64 bytes from 172.30.120.1: icmp_seq=2 ttl=255 time=0.364 ms
64 bytes from 172.30.120.62: icmp_seq=2 ttl=64 time=0.412 ms (DUP!)
64 bytes from 172.30.120.50: icmp_seq=2 ttl=255 time=1.48 ms (DUP!)
64 bytes from 172.30.120.1: icmp_seq=3 ttl=255 time=0.452 ms
64 bytes from 172.30.120.62: icmp_seq=3 ttl=64 time=0.506 ms (DUP!)
64 bytes from 172.30.120.50: icmp_seq=3 ttl=255 time=1.64 ms (DUP!)
Why is that only 3 hosts respond to my ping. Is this bcast address given by ifconfig not the one to be used?
I think this might be the reason why I am not able to carry out an amplification attack on a system on my LAN. I injected ICMP-echo packets with spoofed source address of my friend's host
and sent it to this broadcast address, and was disappointed to see that his bandwidth was not affected...
Kindly explain...
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有些主机根本不响应广播 ping（例如，Windows 默认情况下就是这样配置的）。
Some hosts simply don't respond to broadcast pings (for example, Windows is configured by default this way).
因为在示例中，某些实现通过将广播发送到首选接口来工作，而不是全部。您需要一个中继来发送到所有接口。您可以考虑阅读 RFC 919
Because in example some implementations work by sending the broadcast to the preferred interface, not all of them. You need a relay to send to all interfaces. You may consider reading the RFC 919