-1

You see, in my local Mac's network interface there is no 172.18.1.*:

$ ifconfig
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
    options=1203<RXCSUM,TXCSUM,TXSTATUS,SW_TIMESTAMP>
    inet 127.0.0.1 netmask 0xff000000 
    inet6 ::1 prefixlen 128 
    inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1 
    nd6 options=201<PERFORMNUD,DAD>
gif0: flags=8010<POINTOPOINT,MULTICAST> mtu 1280
stf0: flags=0<> mtu 1280
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
    ether a0:99:9b:17:50:07 
    inet6 fe80::1cd7:aab1:4dc2:a07b%en0 prefixlen 64 secured scopeid 0x4 
    inet 192.168.1.5 netmask 0xffffff00 broadcast 192.168.1.255
    nd6 options=201<PERFORMNUD,DAD>
    media: autoselect
    status: active
en1: flags=963<UP,BROADCAST,SMART,RUNNING,PROMISC,SIMPLEX> mtu 1500
    options=60<TSO4,TSO6>
    ether 4a:00:02:2c:3b:30 
    media: autoselect <full-duplex>
    status: inactive
en2: flags=963<UP,BROADCAST,SMART,RUNNING,PROMISC,SIMPLEX> mtu 1500
    options=60<TSO4,TSO6>
    ether 4a:00:02:2c:3b:31 
    media: autoselect <full-duplex>
    status: inactive
bridge0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
    options=63<RXCSUM,TXCSUM,TSO4,TSO6>
    ether 4a:00:02:2c:3b:30 
    Configuration:
        id 0:0:0:0:0:0 priority 0 hellotime 0 fwddelay 0
        maxage 0 holdcnt 0 proto stp maxaddr 100 timeout 1200
        root id 0:0:0:0:0:0 priority 0 ifcost 0 port 0
        ipfilter disabled flags 0x2
    member: en1 flags=3<LEARNING,DISCOVER>
            ifmaxaddr 0 port 5 priority 0 path cost 0
    member: en2 flags=3<LEARNING,DISCOVER>
            ifmaxaddr 0 port 6 priority 0 path cost 0
    nd6 options=201<PERFORMNUD,DAD>
    media: <unknown type>
    status: inactive
p2p0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 2304
    ether 02:99:9b:17:50:07 
    media: autoselect
    status: inactive
awdl0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1484
    ether 82:c0:df:ea:9f:d6 
    inet6 fe80::80c0:dfff:feea:9fd6%awdl0 prefixlen 64 scopeid 0x9 
    nd6 options=201<PERFORMNUD,DAD>
    media: autoselect
    status: active
utun0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 2000
    inet6 fe80::da49:83e0:5dd9:264%utun0 prefixlen 64 scopeid 0xa 
    nd6 options=201<PERFORMNUD,DAD>

but I can ping the 172.18.1.*.

$ ping 172.18.1.20
PING 172.18.1.20 (172.18.1.20): 56 data bytes
64 bytes from 172.18.1.20: icmp_seq=0 ttl=251 time=9.472 ms
64 bytes from 172.18.1.20: icmp_seq=1 ttl=251 time=17.316 ms
64 bytes from 172.18.1.20: icmp_seq=2 ttl=251 time=7.546 ms
64 bytes from 172.18.1.20: icmp_seq=3 ttl=251 time=6.194 ms
^C
--- 172.18.1.20 ping statistics ---
4 packets transmitted, 4 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 6.194/10.132/17.316/4.308 ms
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2
  • What is your question? You have given information, but never asked anything.
    – YLearn
    Commented Sep 1, 2018 at 17:05
  • @YLearn why i can ping the 172.18.1.20? i have no interface of this ip segment.
    – aircraft
    Commented Sep 1, 2018 at 17:07

1 Answer 1

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3

Note that you can ping across a router by default. If you traceroute 172.18.1.20 you will likely find it behind your default gateway. The ttl=251 indicates that it's three hops away.

If your ping is not supposed to cross a router you need to use a TTL of 1

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