DESCRIPTION
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 a
wait 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 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 default display, show the current bpf(4) peers. To show only the peers listening to a specific interface, use the -I option. If the -s option is present, show the current bpf(4) statistics.
-
-b
-
With the interface display (option -i), show bytes in and out, instead of packets in and out.
-
-d
-
With either interface display (option -i or an interval, as described 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 recognized: inet, for AF_INET; inet6, for AF_INET6; arp, for AF_ARP; ns, for AF_NS; iso, for AF_ISO; atalk, for AF_APPLETALK; mpls, for AF_MPLS; 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 tables. 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-interface statistics on the interface for the specified address_family or protocol, respectively.
-
-h
-
When used with -b in combination with either -i or -I, output "human-readable" byte counts.
-
-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). If the -a options is also present, multicast addresses currently in use are shown for each Ethernet interface 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).
-
-l
-
With the -g option, display wider fields for the IPv6 multicast routing table “Origin” and “Group” columns.
-
-M
-
Extract values associated with the name list from the specified core instead of the default /dev/kmem.
-
-m
-
Show statistics recorded by the mbuf memory management routines (the network manages a private pool of memory buffers).
-
-N
-
Extract the name list from the specified system instead of the default /netbsd.
-
-n
-
Show network addresses and ports as numbers (normally netstat interprets addresses and ports and attempts to display them symbolically). This option may be used with any of the display formats.
-
-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.
-
-q
-
Show software interrupt queue setting/statistics for all protocols.
-
-r
-
Show the routing tables. When -s is also present, show routing statistics instead.
-
-S
-
Show network addresses as numbers (as with -n, but show ports symbolically).
-
-s
-
Show per-protocol statistics. If this option is repeated, counters with a value of zero are suppressed.
-
-T
-
Show MPLS Tags for the routing tables. If multiple tags exists, they will be comma separated, first tag being the BoS one.
-
-t
-
With the -i option, display the current value of the watchdog timer function.
-
-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.
-
-X
-
Force use of sysctl(3) when retrieving information. Some features of netstat may not be (fully) supported when using sysctl(3). This flag forces the use of the latter regardless, and emits a message if a not yet fully supported feature is used in conjunction with it. This flag might be removed at any time; do not rely on its presence.
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 ``*''. You can use the fstat(1) command 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 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 a collection of information 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_PROTO1 |
Protocol specific routing flag #1 |
|
2 |
RTF_PROTO2 |
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) |
|
p |
RTF_ANNOUNCE |
Link level proxy |
|
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 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 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 used 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 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.
The first character of the flags column in the -B option shows the status of the bpf(4) descriptor which has three different values: Idle ('I'), Waiting ('W') and Timed Out ('T'). The second character indicates whether the promisc flag is set. The third character indicates the status of the immediate mode. The fourth character indicates whether the peer will have the ability to see the packets sent. And the fifth character shows the header complete flag status.