Ping、Traceroute
用於監測網路節點是否還活著｜｜抑或用於監測到網路節點的往返時間 RTT, Round Trip Time。
$ping google.com
PING google.com (172.217.24.14): 56 data bytes
64 bytes from 172.217.24.14: icmp_seq=0 ttl=116 time=4.345 ms
$ ping google.com.cn
PING google.com.cn (172.217.175.99): 56 data bytes
64 bytes from 172.217.175.99: icmp_seq=0 ttl=112 time=39.128 ms
用來發現測試點和目標主機之間的路由器。 從測試點對目標主機一次發送不同 TTL 值的多封包，可加速地發現路徑上經過的路由器。
原理：路由器在轉送封包至下一個 hop 之前，會將 TTL 值 -1，直到 0 則回到測試點，（回傳傳輸時間的結果）。
$ traceroute google.com
traceroute to google.com (172.217.24.14), 64 hops max, 52 byte packets
1 192.168.55.1 (192.168.55.1) 2.438 ms 1.181 ms 1.127 ms
2 h254.s98.ts.hinet.net (168.95.98.254) 2.141 ms 2.661 ms 2.341 ms
3 tpe4-3301.hinet.net (168.95.24.58) 2.472 ms 3.809 ms 3.852 ms
4 pcpd-3211.hinet.net (220.128.12.122) 2.616 ms 4.551 ms 3.160 ms
5 72.14.202.34 (72.14.202.34) 4.177 ms
6 * * *
7 209.85.243.196 (209.85.243.196) 5.646 ms
8 108.170.244.139 (108.170.244.139) 4.739 ms
9 tsa01s07-in-f14.1e100.net (172.217.24.14) 3.877 ms
-------------------------------------------------------------------------
$ traceroute yahoo.com
traceroute: Warning: yahoo.com has multiple addresses; using 74.6.143.25
traceroute to yahoo.com (74.6.143.25), 64 hops max, 52 byte packets
1 192.168.55.1 (192.168.55.1) 1.764 ms 0.998 ms 1.139 ms
2 h254.s98.ts.hinet.net (168.95.98.254) 2.160 ms 1.995 ms 1.967 ms
3 tpe4-3302.hinet.net (168.95.25.58) 2.114 ms 2.174 ms 2.474 ms
4 220-128-4-134.hinet-ip.hinet.net (220.128.4.134) 2.733 ms 2.608 ms 2.756 ms
5 r4102-s2.tp.hinet.net (220.128.14.93) 2.483 ms 2.906 ms
r4102-s2.tp.hinet.net (220.128.7.69) 3.455 ms
6 r4002-s2.tp.hinet.net (220.128.31.25) 2.570 ms 2.671 ms 2.559 ms
7 r12-pa.us.hinet.net (202.39.91.29) 127.031 ms 129.162 ms 127.047 ms
8 202-39-82-25.hinet-ip.hinet.net (202.39.82.25) 128.945 ms 136.553 ms 131.378 ms
9 ae-7.pat2.dnx.yahoo.com (216.115.96.115) 151.903 ms 152.112 ms 152.077 ms
10 ae-3.pat2.che.yahoo.com (216.115.96.54) 179.092 ms 176.538 ms 176.435 ms
11 ae-9.pat2.bfz.yahoo.com (216.115.101.199) 186.858 ms
ae-10.pat2.bfy.yahoo.com (184.165.16.0) 197.644 ms 206.787 ms
12 et-2-1-1.pat1.bfz.yahoo.com (216.115.104.77) 186.982 ms
13 et-19-1-0.msr2.bf1.yahoo.com (74.6.227.141) 188.735 ms
14 lo0.fab7-1-gdc.bf2.yahoo.com (74.6.123.238) 188.926 ms 188.787 ms
15 lo0.fab4-1-gdc.bf2.yahoo.com (74.6.123.241) 187.604 ms
16 usw2-1-lbb.bf2.yahoo.com (74.6.98.139) 187.076 ms
倘若主機位置是透過 DHCP 獲得，因為有分配的 ip 位址具時效性，則 DNS 對其無能為力。 DHCP 一般不適用於使用在無邊際路由器和 DNS 伺服器上。