⁣⁣netstat command (Network statistics)

Description

The "netstat" command allows to monitor network connections, network packets statistic for each protocol, to display routing tables and statistics for network interfaces.

Syntax:

net -r print routing table
net -i [clear] print interface table
net -s print IP statistics
net -s{rut} print protocol statistics (raw,udp,tcp)

Parameters

Parameter	Description
-r	Displays the content of the system routing tables. Flags for specific routes have the following meaning: "U" – this routing table element is currently active. "H" – this route leads to a host. If this flag is not set, the route goes to a network. "D" – this route has been created using the "icmp redirect" protocol. "M" – this route has been modified using the "icmp redirect" protocol. "G" – this route is connected to a host. If this flag is not set, it is considered that the route destination is directly connected. "S" – it's a static route, set by the operator using a "route add" command. "1" – a pseudostatic route, set as a result of a "rip static" command. "L" – a route points to a directly connected host (for such a route an APR request may be performed). "C" – when using this route, more specific routes may be created (e.g. using the "L" flag).
-i [clear]	Displays an information about each network interface in the system. "clear" – resets a statistic of inbound / outbound packets and errors.
-s{rut}	Displays statistics for IP and ICMP packets. "r" – if added, statistic of RAW protocol packets is displayed. "u" – statistic of UDP protocol packets is displayed. "t" – statistic of TCP protocol packets is displayed.

Examples

Display the content of the system routing tables using the "-r" parameter.

Routing tables
Destination        Gateway            Flags     Refs     Use  Interface
default            192.168.103.1      UGS         1       47  svi1
10.10.10.0/24      link#2             UC          0        0  eth0
127.0.0.1          127.0.0.1          UH          2       26  lo0
192.168.103.0/24   link#6             UC          0        0  svi1
192.168.103.1      6c:3b:e5:51:e3:8d  UHL         1        0  svi1
192.168.103.20     bc:ee:7b:8d:32:65  UHL         0     1743  svi1
192.168.103.243    08:00:27:54:47:bf  UHL         1    17257  svi1
224.0.0.0/8        127.0.0.1          UGS         0        0  lo0

Reset the statistic of packets and display the information about network interfaces using the "netstat -i [clear]" command.

Name      Network            Address               Ipkts Ierrs      Opkts Oerrs
lo0       Link:                                        0     0          0     0
lo0       127.0.0.1/32       127.0.0.1
eth0      Link:              00043503f7dd              0     0          0     0
eth0      10.10.10.0/24      10.10.10.14
eth1      Link:              00043513f7dd              0     0          0     0
eth1      none               none
rf5.0     Link:              00043523f7dd              0     0          0     0
rf5.0     none               none
null0*    Link:                                        0     0          0     0
svi1      Link:              02043503f7dd              0     0          0     0
svi1      192.168.103.0/24   192.168.103.37

Use the "-s" parameter to display packet statistic.

IP statistic:
ips_total           8584161 (total packets received)
ips_badsum                0 (checksum bad)
ips_tooshort              0 (packet too short)
ips_toosmall              0 (not enough data)
ips_badhlen               0 (ip header length < data size)
ips_badlen                0 (ip length < ip header length)
ips_fragments             0 (fragments received)
ips_fragdropped           0 (frags dropped (dups,ipstat. out of space))
ips_fragtimeout           0 (fragments timed out)
ips_forward               0 (packets forwarded)
ips_cantforward     2496172 (packets rcvd for unreachable dest)
ips_redirectsent          0 (packets forwarded on same net)
ips_noproto               0 (unknown or unsupported protocol)
ips_delivered       6087989 (datagrams delivered to upper level
ips_localout         335787 (total ip packets generated here)
ips_odropped              0 (lost packets due to nobufs,ipstat. etc.)
ips_reassembled           0 (total packets reassembled ok)
ips_fragmented            0 (datagrams sucessfully fragmented)
ips_ofragments            0 (output fragments created)
ips_cantfrag              0 (don't fragment flag was set,ipstat. etc.)
ips_badoptions            0 (error in option processing)
ips_noroute               0 (packets discarded due to no route)
ips_badvers               0 (ip version != 4)
ips_rawout            17401 (total raw ip packets generated)
ips_badfrags              0 (malformed fragments (bad length))
ips_rcvmemdrop            0 (frags dropped for lack of memory)
ips_toolong               0 (ip length > max ip packet size)
 
ICMP Staticstic:
icps_error                0 ( # of calls to icmp_error )
icps_oldshort             0 ( no error 'cuz old ip too short )
icps_oldicmp              0 ( no error 'cuz old was icmp )
icps_badcode              0 ( icmp_code out of range )
icps_tooshort             0 ( packet < ICMP_MINLEN )
icps_checksum             0 ( bad checksum )
icps_badlen               0 ( calculated bound mismatch )
icps_reflect              0 ( number of responses )
icps_bmcastecho           0 ( rejected broadcast icmps )

Display statistic of UDP protocol packets using the "netstat -su" command.

UDP statistic:
udps_ipackets       5878277
udps_opackets         11019
udps_hdrops               0
udps_badsum               0
udps_badlen               0
udps_noport               0
udps_fullsock             0
udps_pcbhashmiss      17511
0.0.0.0:0 snmp
0.0.0.0:161 snmp
0.0.0.0:22534 trap