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Man Pages


Manual Reference Pages  - NETSTAT (1)

NAME

netstat - show network status

CONTENTS

Description
See Also
History
Bugs

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.

.Bk -words netstat [-AaLnSW] [-f protocol_family |-p protocol] [-M core] [-N system]
.Ek
  Display a list of active sockets (protocol control blocks) for each network protocol, for a particular protocol_family, or for a single protocol. If -A is also present, show the address of a protocol control block (PCB) associated with a socket; used for debugging. If -a is also present, show the state of all sockets; normally sockets used by server processes are not shown. If -L is also present, show the size of the various listen queues. The first count shows the number of unaccepted connections, the second count shows the amount of unaccepted incomplete connections, and the third count is the maximum number of queued connections. If -S is also present, show network addresses as numbers (as with -n ) but show ports symbolically.

.Bk -words netstat -i -| -I interface [-abdhntW] [-f address_family] [-M core] [-N system]
.Ek
  Show the state of all network interfaces or a single interface which have been auto-configured (interfaces statically configured into a system, but not located at boot time are not shown). An asterisk ("*") after an interface name indicates that the interface is "down". If -a 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 -b is also present, show the number of bytes in and out. If -d is also present, show the number of dropped packets. If -h is also present, print all counters in human readable form. If -t is also present, show the contents of watchdog timers. If -W is also present, print interface names using a wider field size.

.Bk -words netstat -w wait [-I interface] [-d] [-M core] [-N system]
.Ek
  At intervals of wait seconds, display the information regarding packet traffic on all configured network interfaces or a single interface. If -d is also present, show the number of dropped packets.

.Bk -words netstat -s [-s] [-z] [-f protocol_family |-p protocol] [-M core] [-N system]
.Ek
  Display system-wide statistics for each network protocol, for a particular protocol_family, or for a single protocol. If -s is repeated, counters with a value of zero are suppressed. If -z is also present, reset statistic counters after displaying them.

.Bk -words netstat -i -| -I interface-s [-f protocol_family |-p protocol] [-M core] [-N system]
.Ek
  Display per-interface statistics for each network protocol, for a particular protocol_family, or for a single protocol.

.Bk -words netstat -m [-M core] [-N system]
.Ek
  Show statistics recorded by the memory management routines (mbuf(9)). The network manages a private pool of memory buffers.

.Bk -words netstat -r [-AanW] [-f address_family] [-M core] [-N system]
.Ek
  Display the contents of all routing tables, or a routing table for a particular address_family. If -A is also present, show the contents of the internal Patricia tree structures; used for debugging. If -a is also present, show protocol-cloned routes (routes generated by an RTF_PRCLONING parent route); normally these routes are not shown. When -W is also present, show the path MTU for each route, and print interface names with a wider field size.

.Bk -words netstat -rs [-s] [-M core] [-N system]
.Ek
  Display routing statistics. If -s is repeated, counters with a value of zero are suppressed.

.Bk -words netstat -g [-W] [-f address_family] [-M core] [-N system]
.Ek
  Show information related to multicast (group address) routing. By default, show the IP Multicast virtual-interface and routing tables, and multicast group memberships.

.Bk -words netstat -gs [-s] [-f address_family] [-M core] [-N system]
.Ek
  Show multicast routing statistics. If -s is repeated, counters with a value of zero are suppressed.

Some options have the general meaning:
-f address_family,-p protocol
  Limit display to those records of the specified address_family or a single protocol. The following address families and protocols are recognized:

Family Protocols
inet(AF_INET) bdg, divert, icmp, igmp, ip, ipsec, pim, tcp, udp
inet6(AF_INET6) bdg, icmp6, ip6, ipsec6, rip6, tcp, udp
pfkey(PF_KEY) pfkey
atalk(AF_APPLETALK) ddp
netgraph, ng(AF_NETGRAPH) ctrl, data
ipx(AF_IPX) ipx, spx
unix(AF_UNIX)
link(AF_LINK)
 

The program will complain if protocol is unknown or if there is no statistics routine for it.
-M Extract values associated with the name list from the specified core instead of the default /dev/kmem.
-N Extract the name list from the specified system instead of the default, which is the kernel image the system has booted from.
-n Show network addresses and ports as numbers. Normally netstat attempts to resolve addresses and ports, and display them symbolically.
-W In certain displays, avoid truncating addresses even if this causes some fields to overflow.

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 databases hosts(5) and networks(5), 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 IPv4 "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 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
3      RTF_PROTO3      Protocol specific routing flag #3
B      RTF_BLACKHOLE      Just discard pkts (during updates)
b      RTF_BROADCAST      The route represents a broadcast address
C      RTF_CLONING      Generate new routes on use
c      RTF_PRCLONING      Protocol-specified generate new routes on use
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
W      RTF_WASCLONED      Route was generated as a result of cloning
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 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. By default, this display summarizes information for all interfaces. Information for a specific interface may be displayed with the -I option.

The bpf(4) flags displayed when netstat is invoked with the -B option represents the underlying parameters of the bpf peer. Each flag is represented as a single lower case letter. The mapping between the letters and flags in order of appearance are:
p      Set if listening promiscuously
i      BIOCIMMEDIATE has been set on the device
f      BIOCGHDRCMPLT status: source link addresses are being
  filled automatically
s      BIOCGSEESENT status: see packets originating locally and remotely on the interface.
a      Packet reception generates a signal
l      BIOCLOCK status: descriptor has been locked
 

For more information about these flags, please refer to bpf(4).

SEE ALSO

fstat(1), nfsstat(1), ps(1), sockstat(1), bpf(4), inet(4), route(4), unix(4), hosts(5), networks(5), protocols(5), services(5), iostat(8), route(8), trpt(8), vmstat(8), mbuf(9)

HISTORY

The netstat command appeared in BSD 4.2 .

IPv6 support was added by WIDE/KAME project.

BUGS

The notion of errors is ill-defined.
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August 19, 2005 NETSTAT (1)

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