netstat command in Linux

[Bruno007]

Many of Linux users would be curious to know about the nestat command. The command "nestat" displays statistical information and the current state of network connections, protocols, ports / sockets and appliances. The following is the syntax :

netstat [options]

The following are the options :

• -S displays statistical information about the protocols.
• -I displays statistical information about the network interface.
• -R displays the routing table.
• -C displays statistical information and updates every second
• -L displays information about all sockets that are ready to listen.
• -A displays information about all sockets that are ready to listen and not listen.
• -P displays information about sockets and PID with ProcessName.

[Bruno007]

EXAMPLE :

For statistics about network connections:

netstat

The sample output from above:

Active Internet connections (w / o servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 vhost: 32,803 LocalHost: smtp TIME_WAIT
tcp 0 0 vhost: 32,803 google.com http ESTABLISHED

Where,

• Proto - Specifies the protocol used for the connection.
• Recv-Q - Specifies the number of bytes that are not received.
• Send-Q - Specifies the number of bytes not sent to destination.
• Local Address - Specifies the local address or source port.
• Foreign Address - Specifies the destination address and port.
• State - Specifies the current state of the socket connection.
• ESTABLISHED - Connection is Established.
• TIME_WAIT - Waiting to Receive packets.
• LISTEN - Listening to Establish connection.

[Bruno007]

For the statistics of protocols:

netstat-s

The sample output from above:

• IP
  5193 incoming packets Delivered
  4813 requêtes feels out
• Tcp:
  Received 4033 segments
  4813 segments send out
• Icmp:
  41 ICMP Message Received
  178 ICMP messages feels

For statistics of the network interface:

netstat-i

The sample output from above:
Kernel Interface table
Iface MTU Met RX-OK RX-ERR TX-OK TX-ERR Flg
eth0 1500 0 1308 0 1345 0 BMRU

This is statistical information for the Ethernet card [eth0].

[Bruno007]

DESCRIPTION :

You can see the status of network connections by listing the sockets open. This is the default option: if you do not specify address family, active sockets of all families address will be displayed. With the parameter-e you get some additional information (userid). With the parameter-v you can ask netstat report address families known not supported by the kernel. The-o parameter displays additional information on network timers. By giving -p you will see the PID and process name that owns socket. The-a displays all sockets, including listening socket servers. The address family inet displays Raw sockets, udp and tcp.

FILES :

• / Etc / services - The service mapping file
  
• / Proc / net / dev - Device information
  
• / Proc / net / raw - RAW socket information
  
• / Proc / net / tcp - TCP socket information
  
• / Proc / net / udp - UDP socket information
  
• / Proc / net / igmp - IGMP multicast information
  
• / Proc / net / unix - Unix domain socket information
  
• / Proc / net / ipx - IPX socket information
  
• / Proc/net/ax25 - AX25 socket information
  
• / Proc / net / appeltalk - information sockets DDP (appeltalk)
  
• / Proc / net / nr - NET socket information / ROM
  
• / Proc / net / route - Kernel IP routing information
  
• / Proc/net/ax25_route - AX25 routing information from kernel
  
• / Proc / net / ipx_route - IPX routing information from kernel
  
• / Proc / net / nr_nodes - routing information NET / ROM kernel
  
• / Proc / net / nr_neigh - Neighbourhood NET / ROM kernel
  
• / Proc / net / ip_masquerade - Connecting with masquerade kernel