The netstat command displays the contents of certain network-related data structures in various formats, depending on the options you select.
The netstat command has the several forms shown in the SYNOPSIS section, above, listed as follows:
The first form of the command (with no required arguments) displays a list of active sockets for each protocol.
The second, third, and fourth forms (-g, -p, and -s options) display information from various network data structures.
The fifth form (-m option) displays STREAMS memory statistics.
The sixth form (-i option) shows the state of the interfaces.
The seventh form (-r option) displays the routing table.
The eighth form (-M option) displays the multicast routing table.
The ninth form (-D option) displays the state of DHCP on one or all interfaces.
These forms are described in greater detail below.
With no arguments (the first form), netstat displays connected sockets for PF_INET, PF_INET6, and PF_UNIX, unless modified otherwise by the -f option.
Show the state of all sockets, all routing table entries, or all interfaces, both physical and logical. Normally, listener sockets used by server processes are not shown. Under most conditions, only interface, host, network, and default routes are shown and only the status of physical interfaces is shown.
For the AF_INET address family showing IPv4 information.
For the AF_INET6 address family showing IPv6 information.
For the AF_UNIX address family.
With -r only, limit the display of routes to those matching the specified filter. A filter rule consists of a "keyword:value" pair. The known keywords and the value syntax are:
Selects an address family. This is identical to -f address_family and both syntaxes are supported.
Selects an input or output interface. You can specify the interface by name (such as hme0) or by ifIndex number (for example, 2). If any is used, the filter matches all routes having a specified interface (anything other than null). If none is used, the filter matches all routes having a null interface. Note that you can view the index number (ifIndex) for an interface with the -a option of ifconfig(1M).
Selects a source or destination IP address. If specified with a mask length, then any routes with matching or longer (more specific) masks are selected. If any is used, then all but addresses but 0 are selected. If none is used, then address 0 is selected.
Selects routes tagged with the specified flags. By default, the flags as specified must be set in order to match. With a leading +, the flags specified must be set but others are ignored. With a leading -, the flags specified must not be set and others are permitted.
You can specify multiple instances of -f to specify multiple filters. For example:
% netstat -nr -f outif:hme0 -f outif:hme1 -f dst:10.0.0.0/8
The preceding command displays routes within network 10.0.0.0/8, with mask length 8 or greater, and an output interface of either hme0 or hme1, and excludes all other routes.
Show the multicast group memberships for all interfaces. See DISPLAYS, below.
Show the state of the interfaces that are used for IP traffic. Normally this shows statistics for the physical interfaces. When combined with the -a option, this will also report information for the logical interfaces. See ifconfig(1M).
Show the STREAMS memory statistics.
Show network addresses as numbers. netstat normally displays addresses as symbols. This option may be used with any of the display formats.
Show the net to media tables. See DISPLAYS, below.
Show the routing tables. Normally, only interface, host, network, and default routes are shown, but when this option is combined with the -a option, all routes will be displayed, including cache.
Show per-protocol statistics. When used with the -M option, show multicast routing statistics instead. When used with the -a option, per-interface statistics will be displayed, when available, in addition to statistics global to the system. See DISPLAYS, below.
Verbose. Show additional information for the sockets, STREAMS memory statistics, and the routing table.
Show the state of a particular interface. interface can be any valid interface such as hme0 or le0. Normally, the status and statistics for physical interfaces are displayed. When this option is combined with the -a option, information for the logical interfaces is also reported.
Show the multicast routing tables. When used with the -s option, show multicast routing statistics instead.
Limit display of statistics or state of all sockets to those applicable to protocol. The protocol can be one of ip, ipv6, icmp, icmpv6, igmp, udp, tcp, rawip. rawip can also be specified as raw. The command accepts protocol options only as all lowercase.
Show the status of DHCP configured interfaces.
Display interface statistics accumulated since last display every interval seconds, repeating forever, unless count is specified. When invoked with interval, the first row of netstat output shows statistics accumulated since last reboot.
Display interface statistics the number of times specified by count, at the interval specified by interval.
The display for each active socket shows the local and remote address, the send and receive queue sizes (in bytes), the send and receive windows (in bytes), and the internal state of the protocol.
The numeric host address or network number associated with the socket is used to look up the corresponding symbolic hostname or network name in the hosts or networks database.
If the network or hostname for an address is not known, or if the -n option is specified, the numerical network address is shown. Unspecified, or "wildcard", addresses and ports appear as "*". For more information regarding the Internet naming conventions, refer to inet(7P) and inet6(7P).
The possible state values for TCP sockets are as follows:
Bound, ready to connect or listen.
Closed. The socket is not being used.
Closed, then remote shutdown; awaiting acknowledgment.
Remote shutdown; waiting for the socket to close.
Connection has been established.
Socket closed; shutting down connection.
Socket closed; waiting for shutdown from remote.
Idle, opened but not bound.
Remote shutdown, then closed; awaiting acknowledgment.
Listening for incoming connections.
Initial synchronization of the connection under way.
Actively trying to establish connection.
Wait after close for remote shutdown retransmission.
The form of the display depends upon which of the -g, -m, -p, or -s options you select.
Displays the list of multicast group membership.
Displays the memory usage, for example, STREAMS mblks.
Displays the net to media mapping table. For IPv4, the address resolution table is displayed. See arp(1M). For IPv6, the neighbor cache is displayed.
Displays the statistics for the various protocol layers.
Acting as a gateway.
Not acting as a gateway.
The IPv6 and ICMPv6 protocol layers maintain per-interface statistics. If the -a option is specified with the -s option, then the per-interface statistics as well as the total sums are displayed. Otherwise, just the sum of the statistics are shown.
For the second, third, and fourth forms of the command, you must specify at least -g, -p, or -s. You can specify any combination of these options. You can also specify -m (the fifth form) with any set of the -g, -p, and -s options. If you specify more than one of these options, netstat displays the information for each one of them.
The interface status display lists information for all current interfaces, one interface per line. If an interface is specified using the -I option, it displays information for only the specified interface.
The list consists of the interface name, mtu (maximum transmission unit, or maximum packet size)(see ifconfig(1M)), the network to which the interface is attached, addresses for each interface, and counter associated with the interface. The counters show the number of input packets, input errors, output packets, output errors, and collisions, respectively. For Point-to-Point interfaces, the Net/Dest field is the name or address on the other side of the link.
If the -a option is specified with either the -i option or the -I option, then the output includes names of the physical interface(s), counts for input packets and output packets for each logical interface, plus additional information.
If the -n option is specified, the list displays the IP address instead of the interface name.
If an optional interval is specified, the output will be continually displayed in interval seconds until interrupted by the user or until count is reached. See OPERANDS.
The physical interface is specified using the -I option. When used with the interval operand, output for the -I option has the following format:
input le0 output input (Total) output packets errs packets errs colls packets errs packets errs colls 227681 0 659471 1 502 261331 0 99597 1 502 10 0 0 0 0 10 0 0 0 0 8 0 0 0 0 8 0 0 0 0 10 0 2 0 0 10 0 2 0 0
If the input interface is not specified, the first interface of address family inet or inet6 will be displayed.
The routing table display lists the available routes and the status of each. Each route consists of a destination host or network, and a gateway to use in forwarding packets. The flags column shows the status of the route (U if "up"), whether the route is to a gateway (G), whether it is a redundant route established with the -multirt option (M), whether the route was established using the -setsrc option (S), and whether the route was created dynamically by a redirect (D). If the -a option is specified, there will be routing entries with flags for combined routing and address resolution entries (A), broadcast addresses (B), and the local addresses for the host (L).
Interface routes are created for each interface attached to the local host; the gateway field for such entries shows the address of the outgoing interface.
The use column displays the number of packets sent using a combined routing and address resolution (A) or a broadcast (B) route. For a local (L) route, this count is the number of packets received, and for all other routes it is the number of times the routing entry has been used to create a new combined route and address resolution entry.
The interface entry indicates the network interface utilized for the route.
The DHCP interface information consists of the interface name, its current state, lease information, packet counts, and a list of flags.
The states correlate with the specifications set forth in RFC 2131.
when the lease began;
when lease renewal will begin; and
when the lease will expire.
The interface has a lease obtained through BOOTP.
The interface is busy with a DHCP transaction.
The interface is the primary interface. See dhcpinfo(1).
The interface is in failure state and must be manually restarted.
See attributes(5) for descriptions of the following attributes:
arp(1M), dhcpinfo(1), dhcpagent(1M), ifconfig(1M), iostat(1M), mibiisa(1M), savecore(1M), vmstat(1M), hosts(4), inet_type(4), networks(4), protocols(4), services(4), attributes(5), inet(7P), inet6(7P)
Droms, R., RFC 2131, Dynamic Host Configuration Protocol, Network Working Group, March 1997.
When displaying interface information, netstat honors the DEFAULT_IP setting in /etc/default/inet_type. If it is set to IP_VERSION4, then netstat will omit information relating to IPv6 interfaces, statistics, connections, routes and the like.
However, you can override the DEFAULT_IP setting in /etc/default/inet_type on the command-line. For example, if you have used the command-line to explicitly request IPv6 information by using the inet6 address family or one of the IPv6 protocols, it will override the DEFAULT_IP setting.
The netstat utility obtains TCP statistics from the system by opening /dev/tcp and issuing queries. Because of this, netstat might display an extra, unused connection in IDLE state when reporting connection status.