* Many sites referred for information on this page
1. route -n
The route -n command lists the routing table; the -n option displays the results as IP addresses only and does not attempt to perform a DNS lookup which would replace the IP address with host names if they are available.
The default gateway is always shown with the destination 0.0.0.0 when the -n option is used. If -n is not used, the word "Default" appears in the Destination column of the output. The IP address in the Gateway column is that of the outbound gateway router. The netmask of 0.0.0.0 for the default gateway means that any packet not addressed to the local network or another outbound router by additional entries in the routing table are to be sent to the default gateway regardless of the network class.
The Iface (Interface) column in Figure 1 is the name of the outbound NIC, in this case, eno1. For hosts that are acting as routers, there will likely be at least two and sometimes more NICs used. Each NIC used as a route will be connected to a different physical and logical network. The flags in the Flag column indicate that the route is Up (U) and which is the default Gateway (G). Other flags may also be present.
The netstat -rn command produces very similar results.
1.5 netstat
The netstat command, meaning network statistics, is a Command Prompt command used to display very detailed information about how your computer is communicating with other computers or network devices.
2. arp –a : Prints the arp table
arp –s [pub] to add an entry in the table
arp –a –d to delete all the entries in the ARP table
arp -n
command to view all of the MAC addresses that your host has stored in its arp table.
3. The ifconfig command is used to get the information of active network-interfaces in a Unix-like operating system such as Linux, whereas ipconfig is used in the Windows OS.
4. Ping
—- 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.
5.
7.
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.
8.
nslookup —- Makes queries to the DNS server to translate IP to a name, or vice versa. eg. nslookup facebook.com will gives you the IP of facebook.com
9.
1. route -n
The route -n command lists the routing table; the -n option displays the results as IP addresses only and does not attempt to perform a DNS lookup which would replace the IP address with host names if they are available.
Figure 1: A simple routing table.[root@host1 ~]# route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 0.0.0.0 192.168.0.254 0.0.0.0 UG 100 0 0 eno1 192.168.0.0 0.0.0.0 255.255.255.0 U 100 0 0 eno1
The default gateway is always shown with the destination 0.0.0.0 when the -n option is used. If -n is not used, the word "Default" appears in the Destination column of the output. The IP address in the Gateway column is that of the outbound gateway router. The netmask of 0.0.0.0 for the default gateway means that any packet not addressed to the local network or another outbound router by additional entries in the routing table are to be sent to the default gateway regardless of the network class.
The Iface (Interface) column in Figure 1 is the name of the outbound NIC, in this case, eno1. For hosts that are acting as routers, there will likely be at least two and sometimes more NICs used. Each NIC used as a route will be connected to a different physical and logical network. The flags in the Flag column indicate that the route is Up (U) and which is the default Gateway (G). Other flags may also be present.
The netstat -rn command produces very similar results.
1.5 netstat
The netstat command, meaning network statistics, is a Command Prompt command used to display very detailed information about how your computer is communicating with other computers or network devices.
2. arp –a : Prints the arp table
arp –s
arp –a –d to delete all the entries in the ARP table
arp -n
command to view all of the MAC addresses that your host has stored in its arp table.
3. The ifconfig command is used to get the information of active network-interfaces in a Unix-like operating system such as Linux, whereas ipconfig is used in the Windows OS.
4. Ping
—- 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.
5.
telnet host
7 – echo port,
25 – SMTP, use to send mail
79 – Finger, provides information on other users of the network
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.
6. route add|delete [-net|-host] (ex. route add 192.168.20.0/24 192.168.30.4) to add a route
route flush : it removes all the routes
route flush : it removes all the routes
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 0.0.0.0 in the pace of
IP/SubNet.
route add -net 0.0.0.0 192.168.10.2 : to add a default route
7.
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.
8.
nslookup —- Makes queries to the DNS server to translate IP to a name, or vice versa. eg. nslookup facebook.com will gives you the IP of facebook.com
9.
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
/etc/networks —- network names to ip addresses
/etc/protocols —– protocol names to protocol numbers
/etc/services —- tcp/udp service names to port numbers
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