``Ping'' is a mechanism whereby one can check whether a specific computer is up, and whereby one can estimate the RTT (Round Trip Time) to that computer and the packet loss probability on the round trip path to that computer and back. You have to know either the name or one of the IP addresses of the computer in question. Example: Unfortunately, today (02/08/02) ICMP is disabled by our ISP (due to denial of service attacks) so my examples are internal to NJIT. --- alizarin-41 ott>: nslookup afs2 Server: dns1.njit.edu Address: 128.235.251.10 Name: argerich.njit.edu Address: 128.235.204.109 Aliases: afs2.njit.edu --- I am logged in to alizarin. I ask the ``nslookup'' system what it knows about the computer afs2. The computer that answers is Server: dns1.njit.edu Address: 128.235.251.10 and it tells me the ``official'' name of afs2 is Name: argerich.njit.edu Address: 128.235.204.109 and that it is also known as afs2.njit.edu --- alizarin-42 ott>: ping afs2 afs2 is alive --- I did ``ping afs2''. The echo-request went out and the echo-reply came back, so afs2 is alive. In the next ``ping'' I send 10 echo requests, 1 second in-between, with 100 data bytes per echo request. The IP packets have 108 data bytes (100 ICMP-data and 8 ICMP-header). --- alizarin-43 ott>: ping -s argerich 100 10 PING argerich: 100 data bytes 108 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=0. time=0. ms 108 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=1. time=0. ms 108 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=2. time=0. ms 108 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=3. time=0. ms 108 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=4. time=1. ms 108 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=5. time=0. ms 108 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=6. time=0. ms 108 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=7. time=0. ms 108 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=8. time=0. ms 108 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=9. time=0. ms ----argerich PING Statistics---- 10 packets transmitted, 10 packets received, 0% packet loss round-trip (ms) min/avg/max = 0/0/1 --- All echo replies return. The RTTs (rounded to whole msec) are 9 times 0 msec and once 1 msec. Next I send larger packets (1000 ICMP data bytes): --- alizarin-44 ott>: ping -s 128.235.204.109 1000 10 PING 128.235.204.109: 1000 data bytes 1008 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=0. time=4. ms 1008 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=1. time=4. ms 1008 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=2. time=4. ms 1008 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=3. time=4. ms 1008 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=4. time=4. ms 1008 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=5. time=4. ms 1008 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=6. time=4. ms 1008 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=7. time=4. ms 1008 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=8. time=4. ms 1008 bytes from argerich.njit.edu (128.235.204.109): icmp_seq=9. time=4. ms ----128.235.204.109 PING Statistics---- 10 packets transmitted, 10 packets received, 0% packet loss round-trip (ms) min/avg/max = 4/4/4 --- Now (with larger packets) the RTTs are larger. Each of the 10 RTTs is (about) 4 msec. --- Homework for 02/16/2002: Log in to a Unix computer. Do ``man ping''. Read ``man ping''. Find a computer outside of North America. Preferably in Asia, Africa, or Europe. Estimate the RTT from New Jersey to that computer, and the packet loss probability on the round trip path, for packet sizes 100 bytes and 1000 bytes. If you can not find a foreign computer yourself, try ftp.nl.net . But I prefer you find your own. Hints: If you have a friend with Email address (e.g.) friend@a.b.c.d , there is a high probability that the DOMAIN a.b.c.d contains a COMPUTER called a.b.c.d . If you know a website (e.g) www.bloe.blah or web.foo.oef there is a high probability that there also is a computer called www.bloe.blah or web.foo.oef . etc. Good Luck, Teun Ott. Addition on 04/03/2002: It now is possible to ping from inside NJIT to outside NJIT. Example: --- alizarin-59 ott>: ping -s ftp0.svc.ops.eu.uu.net 100 10 PING ftp0.svc.ops.eu.uu.net: 100 data bytes 108 bytes from ftp0.svc.ops.eu.uu.net (195.129.111.8): icmp_seq=0. time=90. ms 108 bytes from ftp0.svc.ops.eu.uu.net (195.129.111.8): icmp_seq=1. time=91. ms 108 bytes from ftp0.svc.ops.eu.uu.net (195.129.111.8): icmp_seq=2. time=107. ms 108 bytes from ftp0.svc.ops.eu.uu.net (195.129.111.8): icmp_seq=3. time=90. ms 108 bytes from ftp0.svc.ops.eu.uu.net (195.129.111.8): icmp_seq=4. time=92. ms 108 bytes from ftp0.svc.ops.eu.uu.net (195.129.111.8): icmp_seq=5. time=92. ms 108 bytes from ftp0.svc.ops.eu.uu.net (195.129.111.8): icmp_seq=6. time=92. ms 108 bytes from ftp0.svc.ops.eu.uu.net (195.129.111.8): icmp_seq=7. time=90. ms 108 bytes from ftp0.svc.ops.eu.uu.net (195.129.111.8): icmp_seq=8. time=94. ms 108 bytes from ftp0.svc.ops.eu.uu.net (195.129.111.8): icmp_seq=9. time=100. ms ----ftp0.svc.ops.eu.uu.net PING Statistics---- 10 packets transmitted, 10 packets received, 0% packet loss round-trip (ms) min/avg/max = 90/93/107 --- A few minutes ago the RTT was about 164 msec and up. (See traceroute.txt). We see that RTTs are highly variable. (But that was from sdf.lonestar.org to 195.129.111.8 , that is part of the difference). It still is impossible to traceroute from inside NJIT to outside NJIT. Good Luck. Teun Ott.