Netstat Reference Information

The netstat application provides MachTen system information about system network activities. Information about network interface status (netstat -i), network routing configuration (netstat -r) and Internet protocol statistics (netstat -s) are common uses of the application.

Netstat -i

Name Mtu Network Address Ipkts Ierrs Opkts Oerrs Coll
ie0 1500 192.83.246 scratch.tenon.c 69 0 60 0 0
lo0 1536 loopback localhost 0 0 0 0 0

Netstat -r

Routing tables
Destination Gateway Flags Refs Use Interface

INET routing:
default UG 0 27 ie0
localhost UH 1 0 lo0
192.83.246 U 1 30 ie0

Netstat -s

57 total packets received
0 bad header checksums
0 with size smaller than minimum
0 with data size < data length
0 with header length < data size
0 with data length < header length
0 fragments received
0 fragments dropped (dup or out of space)
0 fragments dropped after timeout
0 packets forwarded
0 packets not forwardable
0 redirects sent
18 calls to icmp_error
0 errors not generated 'cuz old message was icmp
Output histogram:
destination unreachable: 18
0 messages with bad code fields
0 messages < minimum length
0 bad checksums
0 messages with bad length
Input histogram:
destination unreachable: 3
time exceeded: 24
0 message responses generated
0 packets sent
0 data packets (0 bytes)
0 data packets (0 bytes) retransmitted
0 ack-only packets (0 delayed)
0 URG only packets
0 window probe packets
0 window update packets
0 control packets
0 packets received
0 acks (for 0 bytes)
0 duplicate acks
0 acks for unsent data
0 packets (0 bytes) received in-sequence
0 completely duplicate packets (0 bytes)
0 packets with some dup. data (0 bytes duped)
0 out-of-order packets (0 bytes)
0 packets (0 bytes) of data after window
0 window probes
0 window update packets
0 packets received after close
0 discarded for bad checksums
0 discarded for bad header offset fields
0 discarded because packet too short
0 connection requests
0 connection accepts
0 connections established (including accepts)
0 connections closed (including 0 drops)
0 embryonic connections dropped
0 segments updated rtt (of 0 attempts)
0 retransmit timeouts
0 connections dropped by rexmit timeout
0 persist timeouts
0 keepalive timeouts
0 keepalive probes sent
0 connections dropped by keepalive
0 incomplete headers
0 bad data length fields
0 bad checksums

Netstat Reference

netstat - show network status

netstat [ -Aan ] [ -f address_family ] [ system ] [ core ]
netstat [ -himnrs ] [ -f address_family ] [ system ] [ core ]
netstat [ -n ] [ -I interface ] interval [ system ] [ core ]
netstat [ -p protocol ] [ system ] [ core ]

The netstat command symbolically displays the contents of various
network-related data structures. There are a number of output
formats, depending on the options for the information presented.
The first form of the command displays a list of active sockets for
each protocol. The second form presents the contents of one of the
other network data structures according to the option selected.
Using the third form, with an interval specified, netstat will
continuously display the information regarding packet traffic on
the configured network interfaces. The fourth form displays
statistics about the named protocol.

The options have the following meaning:

-A With the default display, show the address of any protocol
control blocks associated with sockets; used for debugging.

-a With the default display, show the state of all sockets;
normally sockets used by server processes are not shown. -d
With either interface display (option -i or an interval, as
described below), show the number of dropped packets.

-i Show the state of interfaces which have been auto-configured
(interfaces statically configured into a system, but not
located at boot time are not shown).

-I interface
Show information only about this interface; used with an
interval as described below.

-m Show statistics recorded by the memory management routines (the
network manages a private pool of memory buffers).

-n Show network addresses as numbers (normally netstat interprets
addresses and attempts to display them symbolically). This
option may be used with any of the display formats.

-p protocol
Show statistics about protocol, which is either a well-known
name for a protocol or an alias for it. Some protocol names
and aliases are listed in the file /etc/protocols. A null
response typically means that there are no interesting numbers
to report. The program will complain if protocol is unknown or
if there is no statistics routine for it.

-s Show per-protocol statistics.

-r Show the routing tables. When -s is also present, show routing
statistics instead.

-f address_family
Limit statistics or address control block reports to those of
the specified address family. The following address families
are recognized: inet, for AF_INET, ns, for AF_NS, and unix, for

The arguments, system and core allow substitutes for the defaults
"/vmunix" and "/dev/kmem".

The default display, for active sockets, shows the local and remote
addresses, send and receive queue sizes (in bytes), protocol, and
the internal state of the protocol. Address formats are of the
form "host.port" or "network.port" if a socket's address
specifies a network but no specific host address. When known the
host and network addresses are displayed symbolically according to
the data bases /etc/hosts and /etc/networks, respectively. If a
symbolic name for an address is unknown, or if the -n option is
specified, the address is printed numerically, according to the
address family. For more information regarding the Internet "dot
format," refer to inet(3). Unspecified, or "wildcard",
addresses and ports appear as "*".

The interface display provides a table of cumulative statistics
regarding packets transferred, errors, and collisions. The network
addresses of the interface and the maximum transmission unit
("mtu") are also displayed.

The routing table display indicates the available routes and their
status. Each route consists of a destination host or network and a
gateway to use in forwarding packets. The flags field shows the
state of the route ("U" if "up"), whether the route is to a
gateway ("G"), whether the route was created dynamically by a
redirect ("D"), and whether the route has been modified by a
redirect ("M"). Direct 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 refcnt field
gives the current number of active uses of the route. Connection
oriented protocols normally hold on to a single route for the
duration of a connection while connectionless protocols obtain a
route while sending to the same destination. The use field
provides a count of the number of packets sent using that route.
The interface entry indicates the network interface utilized for
the route.

When netstat is invoked with an interval argument, it displays a
running count of statistics related to network interfaces. This
display consists of a column for the primary interface (the first
interface found during autoconfiguration) and a column summarizing
information for all interfaces. The primary interface may be
replaced with another interface with the -I option. The first line
of each screen of information contains a summary since the system
was last rebooted. Subsequent lines of output show values
accumulated over the preceding interval.

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