NETSTAT(1)

NAME
netstat - show network status

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.

    netstat [-AaLnSTWx] [-f protocol_family | -p protocol] [-M core] [-N system] 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. If -x is present, display socket buffer and tcp timer statistics for each internet socket. When -T is present, display information from the TCP control block, including retransmits, out-of-order packets received, and zero-sized windows advertised.

    netstat -i | -I interface [-abdhnW] [-f address_family] [-M core] [-N system] 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 -W is also present, print interface names using a wider field size.

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

    netstat -s [-s] [-z] [-f protocol_family | -p protocol] [-M core] [-N system] 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.

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

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

    netstat -B [-z] [-I interface] Show statistics about bpf(4) peers. This includes information like how many packets have been matched, dropped and received by the bpf device, also information about current buffer sizes and device states.

    netstat -r [-AanW] [-f address_family] [-M core] [-N system] 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.

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

    netstat -g [-W] [-f address_family] [-M core] [-N system] Display the contents of the multicast virtual interface tables, and multicast forwarding caches. Entries in these tables will appear only when the kernel is actively forwarding multicast sessions. This option is applicable only to the inet and inet6 address families.

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

    netstat -Q Show netisr(9) statistics. The flags field shows available ISR handlers:
    C | NETISR_SNP_FLAGS_M2CPUID | Able to map mbuf to cpu id
    D | NETISR_SNP_FLAGS_DRAINEDCPU | Has queue drain handler
    F | NETISR_SNP_FLAGS_M2FLOW | Able to map mbuf to flow id

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)
        divert, icmp, igmp, ip, ipsec, pim, sctp, tcp, udp
    inet6 (AF_INET6)
        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 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 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).

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 receive
queue.
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.

SEE ALSO
fstat(1), nfsstat(1), procstat(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 4.2BSD.

IPv6 support was added by WIDE/KAME project.

BUGS
The notion of errors is ill-defined.