Network Commands


ping <host> —- sends an ICMP echo message (one packet) to a host. This may go continually until you hit Control-C. Ping means a packet was sent from your machine via ICMP, and echoed at the IP level. ping tells you if the other Host is Up.

telnet host <port> —- talk to “hosts” at the given port number. By default, the telnet port is port 23. Few other famous ports are: 7 – echo port, 25 – SMTP, use to send mail 79 – Finger, provides information on other users of the network

Use control-] to get out of telnet.


Arp is used to translate IP addresses into Ethernet addresses. Root can add and delete arp entries. Deleting them can be useful if an arp entry is malformed or just wrong. Arp entries explicitly added by root are permanent — they can also be by proxy. The arp table is stored in the kernel and manipulated dynamically. Arp entries are cached and will time out and are deleted normally in 20 minutes.

arp –a : Prints the arp table

arp –s <ip_address> <mac_address> [pub] to add an entry in the table

arp –a –d to delete all the entries in the ARP table


netstat –r —- Print routing tables. The routing tables are stored in the kernel and used by ip to route packets to non-local networks.

route add —- The route command is used for setting a static (non-dynamic by hand route) route path in the route tables. All the traffic from this PC to that IP/SubNet will go through the given Gateway IP. It can also be used for setting a default route; i.e., send all packets to a particular gateway, by using in the pace of IP/SubNet.

routed —– The BSD daemon that does dynamic routing. Started at boot. This runs the RIP routing protocol. ROOT ONLY. You won’t be able to run this without root access.

gated —– Gated is an alternative routing daemon to RIP. It uses the OSPF, EGP, and RIP protocols in one place. ROOT ONLY.

traceroute —- Useful for tracing the route of IP packets. The packet causes messages to be sent back from all gateways in between the source and destination by increasing the number of hopes by 1 each time.

netstat –rnf inet : it displays the routing tables of IPv4

sysctl net.inet.ip.forwarding=1 : to enable packets forwarding (to turn a host into a router)

route add|delete [-net|-host] <destination> <gateway> (ex. route add to add a route

route flush : it removes all the routes

route add -net : to add a default route

routed -Pripv2 –Pno_rdisc –d [-s|-q] to execute routed daemon with RIPv2 protocol, without ICMP auto-discovery, in foreground, in supply or in quiet mode

route add : it defines the route used from RIPv2

rtquery –n : to query the RIP daemon on a specific host (manually update the routing table)


nslookup —- Makes queries to the DNS server to translate IP to a name, or vice versa. eg. nslookup will gives you the IP of

ftp <host>water —– Transfer files to host. Often can use login=“anonymous” , p/w=“guest”

rlogin -l —– Logs into the host with a virtual terminal like telnet

Important Files

/etc/hosts —- names to ip addresses

/etc/networks —- network names to ip addresses

/etc/protocols —– protocol names to protocol numbers

/etc/services —- tcp/udp service names to port numbers

Tools and network performance analysis

ifconfig <interface> <address> [up] : start the interface

ifconfig <interface> [down|delete] : stop the interface

ethereal & : it allows you open ethereal background not foreground

tcpdump –i -vvv : tool to capture and analyze packets

netstat –w [seconds] –I [interface] : display network settings and statistics

udpmt –p [port] –s [bytes] target_host : it creates UDP traffic

udptarget –p [port] : it’s able to receive UDP traffic

tcpmt –p [port] –s [bytes] target_host : it creates TCP traffic

tcptarget –p [port] : it’s able to receive TCP traffic


netmask [up]: it allows to subnet the sub-networks


ifconfig sl0 srcIP dstIP : configure a serial interface (do “slattach –l /dev/ttyd0” before, and “sysctl net.inet.ip.forwarding=1“ after)

telnet : to access the switch from a host in its subnetwork

sh ru or show running-configuration : to see the current configurations

configure terminal : to enter in configuration mode

exit : in order to go to the lower configuration mode


vlan n : it creates a VLAN with ID n

no vlan N : it deletes the VLAN with ID N

untagged Y : it adds the port Y to the VLAN N

ifconfig vlan0 create : it creates vlan0 interface

ifconfig vlan0 vlan ID vlandev em0 : it associates vlan0 interface on top of em0, and set the tags to ID

ifconfig vlan0 [up] : to turn on the virtual interface

tagged Y : it adds to the port Y the support of tagged frames for the current VLAN


socklab udp – it executes socklab with udp protocol

sock – it creates a udp socket, it’s equivalent to type sock udp and bind

sendto <Socket ID> <hostname> <port #> – emission of data packets

recvfrom <Socket ID> <byte #> – it receives data from socket

socklab tcp – it executes socklab with tcp protocol

passive – it creates a socket in passive mode, it’s equivalent to socklab, sock tcp, bind, listen

accept – it accepts an incoming connection (it can be done before or after creating the incoming connection)

connect <hostname> <port #> – these two commands are equivalent to socklab, sock tcp, bind, connect

close – it closes the connection

read <byte #> – to read bytes on the socket

write (ex. write ciao, ex. write #10) to write “ciao” or to write 10 bytes on the socket


rm /etc/resolv.conf – it prevent address resolution and make sure your filtering and firewall rules works properly

ipnat –f file_name – it writes filtering rules into file_name

ipnat –l – it gives the list of active rules

ipnat –C –F – it re-initialize the rules table

map em0 → em0 : mapping IP addresses to the interface

map em0 → portmap tcp/udp 20000:50000 : mapping with port

ipf –f file_name : it writes filtering rules into file_name

ipf –F –a : it resets the rule table

ipfstat –I : it grants access to a few information on filtered packets, as well as active filtering rules

Via :

  • system/linux/network-commands.txt
  • Dernière modification: 2020/06/19 20:55
  • (modification externe)