Computer networks -- 2007-2008 -- 5

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Important! These pages are somehow outdated and it is recommended to consult the newer version at Computer networks -- 2008-2009 -- (by Ciprian Crăciun).

Quick links:


In order to successfully accomplish this laboratory, you should be familiar with:

Man pages[edit]

Please consult User:Ciprian Dorin Craciun/Tools/Man.

SSH clients[edit]


This tool is used for checking that a specific host is reachable in an IP network, or for testing the local configuration. PING works by sending ICMP ECHO_REQUEST datagrams to the target host and listening for ICMP ECHO_RESPONSE replies.

ECHO_REQUEST datagrams have an IP and ICMP header, followed by a struct timeval and then an arbitrary number of "pad" bytes used to fill out the packet.

PING provides estimates the round-trip time and records any packet loss, and prints a statistical summary when finished.



user$ ping -c 4

PING ( 56(84) bytes of data.
64 bytes from ( icmp_seq=1 ttl=55 time=10.6 ms
64 bytes from ( icmp_seq=2 ttl=55 time=10.5 ms
64 bytes from ( icmp_seq=3 ttl=55 time=10.4 ms
64 bytes from ( icmp_seq=4 ttl=55 time=10.7 ms

--- ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3015ms
rtt min/avg/max/mdev = 10.449/10.592/10.717/0.165 ms


The ping tool can be used for:

  • fault isolation -- It is first run on the localhost in order to verify that the local network interface is running. Then, hosts and gateways further and further away should be "pinged" in order to check their status.
  • metrics -- PING computer Round-trip times and packet loss statistics. When PING sends the specified number of packets (and possibly has received them) a summary is displayed


Although RFC 1122 prescribes that any host must accept an echo-request and issue an echo-reply in return, one finds that this standard is frequently not followed on the public Internet.


arping is similar in functionality with ping, but operates by using the ARP protocol (opposed to ping which uses ICMP). Due to the usage of the ARP protocol the arping tool is only useful in the local network or in networks that provide an PROXY ARP.



root# arping -I eth1

ARPING from eth1
Unicast reply from [00:1D:60:95:77:16]  2.024ms
Unicast reply from [00:1D:60:95:77:16]  1.083ms
Unicast reply from [00:1D:60:95:77:16]  1.601ms
Sent 3 probes (1 broadcast(s))
Received 3 response(s)

nslookup and dig[edit]

netcat and telnet[edit]





Wireshark and tcpdump[edit]