Manual Pages  — NETSTAT

• SYNOPSIS
• DESCRIPTION
• GENERAL OPTIONS
• SEE ALSO
• HISTORY
• BUGS

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 -x flag causes netstat to output all the information recorded about data stored in the socket buffers. The fields are:

R-MBUF	Number of mbufs in the receive queue.
S-MBUF	Number of mbufs in the send queue.
R-CLUS	Number of clusters, of any type, in the receivequeue.
S-CLUS	Number of clusters, of any type, in the send queue.
R-HIWA	Receive buffer high water mark, in bytes.
S-HIWA	Send buffer high water mark, in bytes.
R-LOWA	Receive buffer low water mark, in bytes.
S-LOWA	Send buffer low water mark, in bytes.
R-BCNT	Receive buffer byte count.
S-BCNT	Send buffer byte count.
R-BMAX	Maximum bytes that can be used in the receive buffer.
S-BMAX	Maximum bytes that can be used in the send buffer.
rexmt	Time, in seconds, to fire Retransmit Timer, or 0 if not armed.
persist	Time, in seconds, to fire Retransmit Persistence, or 0 if not armed.
keep	Time, in seconds, to fire Keep Alive, or 0 if not armed.
2msl	Time, in seconds, to fire 2*msl TIME_WAIT Timer, or 0 if not armed.
delack	Time, in seconds, to fire Delayed ACK Timer, or 0 if not armed.
rcvtime	Time, in seconds, since last packet received.

When netstat is invoked with -i (all interfaces) or -I interface, it 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.

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 interface option.

The bpf(4) flags displayed when netstat is invoked with the -B option represent 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 beingfilled automatically
s	BIOCGSEESENT status: see packets originating locally andremotely 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).

When netstat is invoked with the routing table option -r, it lists 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
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 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.