• ping ipaddress/hostname 命令可以显示计算机是否正在运行以及网络连接是否正常。该命令使用互联网控制消息协议(Internet Control Message Protocol， ICMP)中的Echo功能。 该命令通过网络将一个小型报文发至指定的 IP地址。 如果可以收到该报文的应答消息， 则表明这条计算机网络连接是存活的。该命令还可以显示出
  在源计算机和目的计算机之间存在着多少个中间跳数。
  
• route 命令可以显示路由表内容，在路由表中增删路由，以及清空所有的路由信息。如果ping命令不起作用，即网络连接没有激活，那么可以使用 arp命令来确定问题根源。该命令的-a选项可以确定硬件地址是否正确地关联到适当的系统上，其他可用的选项包括清空arp缓存、向 arp缓存中添加信息等 。
• ifconfig 可以确定主机的介质访问控制地址。如果网络上存在着另一台具有相同 IP地址的主机，则该主机的介质访问控制地址可能已存在于本机的 arp缓存中。在这种情况下， 可以使用 arp命令来删除缓存中保存的地址并将正确的地址添加到arp缓存中。
• traceroute 可以跟踪报文的某条路由路径。 当报文在网络中传输时， 该命令能够测量报文在每一跳(路由器)之间传输所用的时间，并标识出每一跳的地址。
•  ethtool 可以查询并修改以太网设备的设置参数。每个设备都被分配一个标识编号，例如对于系统中的 n个以太网设备，其编号为 eth0、 eth1…ethn。 ethtool工具使用这种设备名称来查询/修改设置信息。
• tcpdump 对网络报文进行嗅探，能够捕获计算机在网络上可见的所有报文。该工具可用于网络监视、 协议调试以及数据获取等功能。该命令将 NIC设置为杂收(promiscuous)模式以便捕获所有流经物理线路的报文。该命令提供了大量关于输出结果的过滤选项， 可以只显示需要关注的报文类型。但其缺点是缓冲区可能会发生溢出。 在高带宽网络上执行 tcpdump操作还有可能会丢弃报文， 即 tcpdump的处理速度无法匹配报文的传输速率。
• ethereal是另一种类似于 tcpdump的网络嗅探工具， 可以读取 tcpdump所捕获的文
  件。
• host 工具用于从域名系统(Domain Name System)中获取指定 IP地址的主机名。该工具远比 nslookup更灵活，并且适于在 shell脚本中使用。

[solarflar@localhost ~]$ netstat 
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State      
tcp        0      0 192.168.75.189:ssh      172.29.8.150:51963      TIME_WAIT  
tcp        0      0 192.168.75.189:ssh      192.168.194.59:48183    ESTABLISHED
tcp        0     52 192.168.75.189:ssh      172.29.8.150:52999      ESTABLISHED
tcp        0      0 192.168.75.189:ssh      192.168.194.55:19001    ESTABLISHED
tcp        0      0 192.168.75.189:ssh      192.168.194.55:17796    ESTABLISHED
Active UNIX domain sockets (w/o servers)
Proto RefCnt Flags       Type       State         I-Node   Path
unix  2      [ ]         DGRAM                    29748    /run/systemd/shutdownd
unix  2      [ ]         DGRAM                    11475    /run/systemd/notify
unix  5      [ ]         DGRAM                    11496    /run/systemd/journal/socket
unix  16     [ ]         DGRAM                    11498    /dev/log
unix  3      [ ]         STREAM     CONNECTED     37002    /run/systemd/journal/stdout
unix  3      [ ]         STREAM     CONNECTED     23698    /run/systemd/journal/stdout

[solarflar@localhost ~]$ netstat -i
Kernel Interface table
Iface      MTU    RX-OK RX-ERR RX-DRP RX-OVR    TX-OK TX-ERR TX-DRP TX-OVR Flg
eno1      1500 2034333467      0    182 0      3548944453      0      0      0 BMRU
eno2      1500        0      0      0 0             0      0      0      0 BMU
eno3      1500        0      0      0 0             0      0      0      0 BMU
eno4      1500        0      0      0 0             0      0      0      0 BMU
enp131s0  1500 1591418974      0  52118 0      486169278      0      0      0 BMRU
enp131s0  1500        0      0      0 0             0      0      0      0 BMU
lo       65536 594975131      0      0 0      594975131      0      0      0 LRU

[solarflar@localhost ~]$ netstat -s
Ip:4603736451 total packets received0 forwarded0 incoming packets discarded4423014584 incoming packets delivered4398660228 requests sent out42782 outgoing packets dropped22 dropped because of missing route36615113 reassemblies required7960999 packets reassembled ok1967473 fragments received ok9530756 fragments created
Icmp:1236458 ICMP messages received1826 input ICMP message failed.ICMP input histogram:destination unreachable: 1236301echo requests: 71echo replies: 74timestamp request: 4address mask request: 8405465 ICMP messages sent0 ICMP messages failedICMP output histogram:destination unreachable: 405135echo request: 255echo replies: 71timestamp replies: 4
IcmpMsg:InType0: 74InType3: 1236301InType8: 71InType13: 4InType17: 8OutType0: 71OutType3: 405135OutType8: 255OutType14: 4
Tcp:554771 active connections openings5422 passive connection openings551155 failed connection attempts1918 connection resets received6 connections established59059673 segments received69625408 segments send out24976 segments retransmited6 bad segments received.70797 resets sentInCsumErrors: 1
Udp:4325339161 packets received999602 packets to unknown port received.396416917 packet receive errors4345291695 packets sent10913928 receive buffer errors37346 send buffer errors
UdpLite:
TcpExt:32 invalid SYN cookies received36 resets received for embryonic SYN_RECV sockets73 packets pruned from receive queue because of socket buffer overrun4652 TCP sockets finished time wait in fast timer169068 delayed acks sent36 delayed acks further delayed because of locked socketQuick ack mode was activated 3651 times26222704 packets directly queued to recvmsg prequeue.3711962702 bytes directly in process context from backlog15106819553 bytes directly received in process context from prequeue2655495 packet headers predicted31357215 packets header predicted and directly queued to user3062089 acknowledgments not containing data payload received31242645 predicted acknowledgments2010 times recovered from packet loss by selective acknowledgementsDetected reordering 2 times using FACK2 congestion windows fully recovered without slow start308 congestion windows recovered without slow start by DSACK267 congestion windows recovered without slow start after partial ackTCPLostRetransmit: 22612 timeouts after SACK recovery1 timeouts in loss state4619 fast retransmits3282 forward retransmits413 retransmits in slow start518 other TCP timeoutsTCPLossProbes: 15920TCPLossProbeRecovery: 1404241 SACK retransmits failed7152 packets collapsed in receive queue due to low socket buffer4731 DSACKs sent for old packets2 DSACKs sent for out of order packets15907 DSACKs received11 DSACKs for out of order packets received10 connections reset due to unexpected data42 connections reset due to early user close206 connections aborted due to timeoutTCPDSACKIgnoredOld: 1TCPDSACKIgnoredNoUndo: 13716TCPSpuriousRTOs: 40TCPSackShifted: 19573TCPSackMerged: 2838TCPSackShiftFallback: 15102TCPRetransFail: 6TCPRcvCoalesce: 172790TCPOFOQueue: 62042TCPOFOMerge: 2TCPChallengeACK: 199TCPSYNChallenge: 5TCPAutoCorking: 133696TCPFromZeroWindowAdv: 20TCPToZeroWindowAdv: 20TCPWantZeroWindowAdv: 1589TCPSynRetrans: 33TCPOrigDataSent: 60622666TCPHystartTrainDetect: 154TCPHystartTrainCwnd: 3092TCPHystartDelayDetect: 21TCPHystartDelayCwnd: 899TCPACKSkippedSeq: 197TCPACKSkippedChallenge: 1
IpExt:InMcastPkts: 3045103079OutMcastPkts: 2727644667InBcastPkts: 16567InOctets: 1654553951951OutOctets: 351194071831InMcastOctets: 1058583515712OutMcastOctets: 221466960723InBcastOctets: 2639362InNoECTPkts: 4603779373InECT0Pkts: 30
[solarflar@localhost ~]$ 

[solarflar@localhost ~]$ nfsstat 
Server rpc stats:
calls      badcalls   badclnt    badauth    xdrcall
0          0          0          0          0