Display network status information, such as statistics about the state of network interfaces, routing tables, and various protocols, with the netstat command.
$ netstat [-i] [-r] [-s] |
-i |
Displays the state of the TCP/IP interfaces |
-r |
Displays the IP routing table |
-s |
Displays statistics for the UDP, TCP, ICMP, and IGMP protocols |
For more information, see netstat(1M).
The following example shows output from the netstat -i command, which displays the state of the interfaces used for TCP/IP traffic.
$ netstat -i Name Mtu Net/Dest Address Ipkts Ierrs Opkts Oerrs Collis Queue lo0 8232 software localhost 1280 0 1280 0 0 0 le0 1500 loopback venus 1628480 0 347070 16 39354 0 |
This display shows how many packets a machine has transmitted and received on each interface. A machine with active network traffic should show both Ipkts and Opkts continually increasing.
Calculate the network collisions rate by dividing the number of collision counts (Collis) by the number of out packets (Opkts). In the previous example, the collision rate is 11 percent. A network-wide collision rate greater than 5 to 10 percent can indicate a problem.
Calculate the input packet error rate by dividing the number of input errors by the total number of input packets (Ierrs/Ipkts). The output packet error rate is the number of output errors divided by the total number of output packets (Oerrs/Opkts). If the input error rate is high (over 0.25 percent), the host might be dropping packets.
The following example shows output from the netstat -s command, which displays the per-protocol statistics for the UDP, TCP, ICMP, and IGMP protocols.
UDP udpInDatagrams =196543 udpInErrors = 0 udpOutDatagrams =187820 TCP tcpRtoAlgorithm = 4 tcpRtoMin = 200 tcpRtoMax = 60000 tcpMaxConn = -1 tcpActiveOpens = 26952 tcpPassiveOpens = 420 tcpAttemptFails = 1133 tcpEstabResets = 9 tcpCurrEstab = 31 tcpOutSegs =3957636 tcpOutDataSegs =2731494 tcpOutDataBytes =1865269594 tcpRetransSegs = 36186 tcpRetransBytes =3762520 tcpOutAck =1225849 tcpOutAckDelayed =165044 tcpOutUrg = 7 tcpOutWinUpdate = 315 tcpOutWinProbe = 0 tcpOutControl = 56588 tcpOutRsts = 803 tcpOutFastRetrans = 741 tcpInSegs =4587678 tcpInAckSegs =2087448 tcpInAckBytes =1865292802 tcpInDupAck =109461 tcpInAckUnsent = 0 tcpInInorderSegs =3877639 tcpInInorderBytes =-598404107 tcpInUnorderSegs = 14756 tcpInUnorderBytes =17985602 tcpInDupSegs = 34 tcpInDupBytes = 32759 tcpInPartDupSegs = 212 tcpInPartDupBytes =134800 tcpInPastWinSegs = 0 tcpInPastWinBytes = 0 tcpInWinProbe = 456 tcpInWinUpdate = 0 tcpInClosed = 99 tcpRttNoUpdate = 6862 tcpRttUpdate =435097 tcpTimRetrans = 15065 tcpTimRetransDrop = 67 tcpTimKeepalive = 763 tcpTimKeepaliveProbe= 1 tcpTimKeepaliveDrop = 0 IP ipForwarding = 2 ipDefaultTTL = 255 ipInReceives =11757234 ipInHdrErrors = 0 ipInAddrErrors = 0 ipInCksumErrs = 0 ipForwDatagrams = 0 ipForwProhibits = 0 ipInUnknownProtos = 0 ipInDiscards = 0 ipInDelivers =4784901 ipOutRequests =4195180 ipOutDiscards = 0 ipOutNoRoutes = 0 ipReasmTimeout = 60 ipReasmReqds = 8723 ipReasmOKs = 7565 ipReasmFails = 1158 ipReasmDuplicates = 7 ipReasmPartDups = 0 ipFragOKs = 19938 ipFragFails = 0 ipFragCreates =116953 ipRoutingDiscards = 0 tcpInErrs = 0 udpNoPorts =6426577 udpInCksumErrs = 0 udpInOverflows = 473 rawipInOverflows = 0 ICMP icmpInMsgs =490338 icmpInErrors = 0 icmpInCksumErrs = 0 icmpInUnknowns = 0 icmpInDestUnreachs = 618 icmpInTimeExcds = 314 icmpInParmProbs = 0 icmpInSrcQuenchs = 0 icmpInRedirects = 313 icmpInBadRedirects = 5 icmpInEchos = 477 icmpInEchoReps = 20 icmpInTimestamps = 0 icmpInTimestampReps = 0 icmpInAddrMasks = 0 icmpInAddrMaskReps = 0 icmpInFragNeeded = 0 icmpOutMsgs = 827 icmpOutDrops = 103 icmpOutErrors = 0 icmpOutDestUnreachs = 94 icmpOutTimeExcds = 256 icmpOutParmProbs = 0 icmpOutSrcQuenchs = 0 icmpOutRedirects = 0 icmpOutEchos = 0 icmpOutEchoReps = 477 icmpOutTimestamps = 0 icmpOutTimestampReps= 0 icmpOutAddrMasks = 0 icmpOutAddrMaskReps = 0 icmpOutFragNeeded = 0 icmpInOverflows = 0 IGMP: 0 messages received 0 messages received with too few bytes 0 messages received with bad checksum 0 membership queries received 0 membership queries received with invalid field(s) 0 membership reports received 0 membership reports received with invalid field(s) 0 membership reports received for groups to which we belong 0 membership reports sent |
The following example shows output from the netstat -r command, which displays the IP routing table.
Routing Table: Destination Gateway Flags Ref Use Interface ------------------ -------------------- ----- ----- ------ --------- localhost localhost UH 0 2817 lo0 earth-bb pluto U 3 14293 le0 224.0.0.0 pluto U 3 0 le0 default mars-gate UG 0 14142 |
The fields in the netstat -r report are described in Table 37-2.
Table 37-2 Output From the netstat -r Command
Field Name |
|
Description |
---|---|---|
Flags |
U G H D |
The route is up The route is through a gateway The route is to a host The route was dynamically created using a redirect |
Ref |
|
Shows the current number of routes sharing the same link layer |
Use |
|
Indicates the number of packets sent out |
Interface |
|
Lists the network interface used for the route |