netstat(1)
- NetBSD Manual Pages
NETSTAT(1) NetBSD Reference Manual NETSTAT(1)
NAME
netstat - show network status
SYNOPSIS
netstat [-Aan] [-f address_family] [-M core] [-N system]
netstat [-dgiLmnrsSv] [-f address_family] [-M core] [-N system]
netstat [-dn] [-I interface] [-M core] [-N system] [-w wait]
netstat [-p protocol] [-M core] [-N system]
netstat [-p protocol] [-M core] [-N system] -P pcbaddr
netstat [-p protocol] [-i] [-I Interface]
netstat [-s] [-f address_family] [-i] [-I Interface]
DESCRIPTION
The netstat command symbolically displays the contents of various net-
work-related data structures. There are a number of output formats, de-
pending 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 struc-
tures according to the option selected. Using the third form, with a
wait interval specified, netstat will continuously display the informa-
tion regarding packet traffic on the configured network interfaces. The
fourth form displays statistics about the named protocol. The fifth and
sixth forms display per interface statistics for the specified protocol
or address family.
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.
-b With the interface display (option -i), show bytes in and out, in-
stead of packets in and out.
-d With either interface display (option -i or an interval, as de-
scribed below), show the number of dropped packets.
-f address_family
Limit statistics or address control block reports to those of the
specified address family. The following address families are rec-
ognized: inet, for AF_INET; inet6, for AF_INET6; arp, for AF_ARP;
ns, for AF_NS; iso, for AF_ISO; atalk, for AF_APPLETALK; and local
or unix, for AF_LOCAL.
-g Show information related to multicast (group address) routing. By
default, show the IP Multicast virtual-interface and routing ta-
bles. If the -s option is also present, show multicast routing
statistics.
-I interface
Show information about the specified interface; used with a wait
interval as described below. If the -f address_family option (with
the -s option) or the -p protocol option is present, show per-in-
terface statistics on the interface for the specified
address_family or protocol, respectively.
-i Show the state of interfaces which have been auto-configured (in-
terfaces statically configured into a system, but not located at
boot time are not shown). If the -a options is also present, mul-
ticast addresses currently in use are shown for each Ethernet in-
terface and for each IP interface address. Multicast addresses are
shown on separate lines following the interface address with which
they are associated. If the -f address_family option (with the -s
option) or the -p protocol option is present, show per-interface
statistics on all interfaces for the specified address_family or
protocol, respectively.
-L Don't show link-level routes (e.g., IPv4 ARP or IPv6 neighbour
cache).
-M Extract values associated with the name list from the specified
core instead of the default /dev/kmem.
-m Show statistics recorded by the memory management routines (the
network manages a private pool of memory buffers).
-N Extract the name list from the specified system instead of the de-
fault /netbsd.
-n Show network addresses and ports as numbers (normally netstat in-
terprets addresses and ports and attempts to display them symboli-
cally). This option may be used with any of the display formats.
-S Show network addresses as numbers (as with -n) but show ports sym-
bolically).
-P pcbaddr
Dump the contents of the protocol control block (PCB) located at
kernel virtual address pcbaddr. This address may be obtained using
the -A flag. The default protocol is TCP, but may be overridden
using the -p flag.
-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. If this option is repeated, counters
with a value of zero are suppressed.
-r Show the routing tables. When -s is also present, show routing
statistics instead.
-v Show extra (verbose) detail for the routing tables (-r), or avoid
truncation of long addresses.
-w wait
Show network interface statistics at intervals of wait seconds.
The default display, for active sockets, shows the local and remote ad-
dresses, send and receive queue sizes (in bytes), protocol, and the in-
ternal state of the protocol. Address formats are of the form
``host.port'' or ``network.port'' if a socket's address specifies a net-
work but no specific host address. When known the host and network ad-
dresses 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 numeri-
cally, according to the address family. For more information regarding
the Internet ``dot format,'' refer to inet(3)). Unspecified, or ``wild-
card'', addresses and ports appear as ``*''. You can use the fstat(1) to
find out which process or processes hold references to a socket.
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 dis-
played.
The routing table display indicates the available routes and their sta-
tus. Each route consists of a destination host or network and a gateway
to use in forwarding packets. The flags field shows a collection of in-
formation about the route stored as binary choices. The individual flags
are discussed in more detail in the route(8) and route(4) manual pages.
The mapping between letters and flags is:
1 RTF_PROTO2 Protocol specific routing flag #1
2 RTF_PROTO1 Protocol specific routing flag #2
B RTF_BLACKHOLE Just discard pkts (during updates)
C RTF_CLONING Generate new routes on use
c RTF_CLONED Cloned routes (generated from RTF_CLONING)
D RTF_DYNAMIC Created dynamically (by redirect)
G RTF_GATEWAY Destination requires forwarding by intermediary
H RTF_HOST Host entry (net otherwise)
L RTF_LLINFO Valid protocol to link address translation.
M RTF_MODIFIED Modified dynamically (by redirect)
R RTF_REJECT Host or net unreachable
S RTF_STATIC Manually added
U RTF_UP Route usable
X RTF_XRESOLVE External daemon translates proto to link address
Direct routes are created for each interface attached to the local host;
the gateway field for such entries shows the address of the outgoing in-
terface. 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 mtu entry
shows the mtu associated with that route. This mtu value is used as the
basis for the TCP maximum segment size. The 'L' flag appended to the mtu
value indicates that the value is locked, and that path mtu discovery is
turned off for that route. A `-' indicates that the mtu for this route
has not been set, and a default TCP maximum segment size will be used.
The interface entry indicates the network interface utilized for the
route.
When netstat is invoked with the -w option and a wait interval argument,
it displays a running count of statistics related to network interfaces.
An obsolescent version of this option used a numeric parameter with no
option, and is currently supported for backward compatibility. This dis-
play 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 in-
terface 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.
SEE ALSO
fstat(1), nfsstat(1), ps(1), vmstat(1), inet(3), hosts(5), networks(5),
protocols(5), services(5), iostat(8), trpt(8), trsp(8)
HISTORY
The netstat command appeared in 4.2BSD. IPv6 support was added by
WIDE/KAME project.
BUGS
The notion of errors is ill-defined.
NetBSD 1.6 December 13, 1999 3
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