案例一 一天，小王突然急匆匆的来找我，他说：“我在机子上刚装的redhat怎么老也ping不通服务器，我网卡的驱动都安装了，ping 自己的两块网卡的IP都能通，可就时访问不了服务器。我输入http://172.31.0.101就提示‘当试图与172.31.0.101联系时，连接被拒绝’” 我来到小王的机器前查看了一下网络配置。 [root@rhas root]# ifconfig -a eth0 Link encap:Ethernet HWaddr 00:D0:B7:C6:8F:1D inet addr:172.31.0.200 Bcast:172.31.0.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:16 errors:0 dropped:0 overruns:0 frame:0 TX packets:5 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:1306 (1.2 Kb) TX bytes:210 (210.0 b) Interrupt:10 Base address:0xe800 Memory:d9100000-d9100038 eth1 Link encap:Ethernet HWaddr 00:01:03:40:A4:15 inet addr:172.31.0.201 Bcast:172.31.0.255 Mask:255.255.255.0 UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:32 errors:0 dropped:0 overruns:0 carrier:32 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 b) TX bytes:1920 (1.8 Kb) Interrupt:11 Base address:0xec00 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:1430 errors:0 dropped:0 overruns:0 frame:0 TX packets:1430 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:143776 (140.4 Kb) TX bytes:143776 (140.4 Kb) [root@rhas root]# route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 172.31.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1 172.31.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1 169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth1 127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 0 lo 0.0.0.0 172.31.0.254 0.0.0.0 UG 0 0 0 eth1 到这一步我猜想网线可能没有插到默认网关对应的网卡上即eth1(嗨！小王的机器被镶在桌子里不太好挪动。连他自己把网线插在那块卡上都不知道了。) 接着我在一机子上ping 172.31.0.200和172.31.0.201,在小王的机器监听 [root@rhas root]# tcpdump tcpdump: listening on eth0 19:32:29.109283 172.31.0.101 > 172.31.0.200: icmp: echo request (DF) 19:32:30.109337 172.31.0.101 > 172.31.0.200: icmp: echo request (DF) 19:32:31.109418 172.31.0.101 > 172.31.0.200: icmp: echo request (DF) 19:32:42.670162 172.31.0.101 > 172.31.0.201: icmp: echo request (DF) 19:32:43.670218 172.31.0.101 > 172.31.0.201: icmp: echo request (DF) 19:32:44.670291 172.31.0.101 > 172.31.0.201: icmp: echo request (DF) ........................ ........................ 19:32:56.671040 172.31.0.101 > 172.31.0.201: icmp: echo request (DF) 19:32:57.671064 172.31.0.101 > 172.31.0.201: icmp: echo request (DF) 19:32:58.671133 172.31.0.101 > 172.31.0.201: icmp: echo request (DF) 19:32:59.671187 172.31.0.101 > 172.31.0.201: icmp: echo request (DF) 19:33:00.671257 172.31.0.101 > 172.31.0.201: icmp: echo request (DF) 19:33:01.671349 172.31.0.101 > 172.31.0.201: icmp: echo request (DF) 19:33:02.671377 172.31.0.101 > 172.31.0.201: icmp: echo request (DF) 19:33:03.671441 172.31.0.101 > 172.31.0.201: icmp: echo request (DF) 36 packets received by filter 0 packets dropped by kernel 没有回应，看一下Firewall的设置。 [root@rhas3 123]# iptables -L -n Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination 又不是防火墙的问题，想了一下，我越发肯定刚才的想法是正确的。 [root@rhas root]# cat /etc/modules.conf alias eth0 e100 alias eth1 3c59x alias sound-slot-0 via82cxxx_audio post-install sound-slot-0 /bin/aumix-minimal -f /etc/.aumixrc -L >/dev/null 2>&1 : pre-remove sound-slot-0 /bin/aumix-minimal -f /etc/.aumixrc -S >/dev/null 2>&1 : alias usb-controller usb-uhci [root@rhas root]#mii-tool eth0: negotiated 100baseTx-Fd flow-control, link ok eth1: no linkk 找到原因了，果然是插反了。既然不方便换端口最简单的就把eth1即3Com网卡宕调就OK了 当然也可以把两块网卡分配在不同的网段。 [root@rhas root]# vi /etc/sysconfig/network-scripts/ifcfg-eth1 # 3Com Corporation3c905C-TX/TX-M [Tornado] DEVICE=eth1 BOOTPROTO=static BROADCAST=172.31.0.255 HWADDR=00:01:03:40:A4:15 IPADDR=172.31.0.201 NETMASK=255.255.255.0 NETWORK=172.31.0.0 ONBOOT=no TYPE=Ethernet~ ~ ~ "/etc/sysconfig/network-scripts/ifcfg-eth1" [已转换] 10L, 207C 9,1 全部 或者在启动哦时根本不要加载3Com网卡的驱动哦。 从启动我们的网络 [root@rhas root]# service network restart 正在关闭接口 eth0： [ 确定 ] 关闭环回接口： [ 确定 ] 设置网络参数： [ 确定 ] 弹出环回接口： [ 确定 ] 弹出界面 eth0： [ 确定 ] [root@rhas root]# [root@rhas root]# [root@rhas root]# [root@rhas root]# ifconfig eth0 Link encap:Ethernet HWaddr 00:D0:B7:C6:8F:1D inet addr:172.31.0.200 Bcast:172.31.0.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:68 errors:0 dropped:0 overruns:0 frame:0 TX packets:10 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:5560 (5.4 Kb) TX bytes:504 (504.0 b) Interrupt:10 Base address:0xe800 Memory:d9100000-d9100038 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:2041 errors:0 dropped:0 overruns:0 frame:0 TX packets:2041 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:209184 (204.2 Kb) TX bytes:209184 (204.2 Kb) [root@rhas root]# ping 172.31.0.101 PING 172.31.0.101 (172.31.0.101) 56(84) bytes of data. 64 bytes from 172.31.0.101: icmp_seq=0 ttl=64 time=0.542 ms 64 bytes from 172.31.0.101: icmp_seq=1 ttl=64 time=0.270 ms --- 172.31.0.101 ping statistics --- 2 packets transmitted, 2 received, 0% packet loss, time 1004ms rtt min/avg/max/mdev = 0.270/0.406/0.542/0.136 ms, pipe 2 [root@rhas root]# route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 172.31.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0 169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth0 127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 0 lo 0.0.0.0 172.31.0.254 0.0.0.0 UG 0 0 0 eth0 [root@rhas root]# 此时访问网络没有问题，故障排除。
案例二 由此我又想相类似的案例，一win98用户错将”TCP/IP-->拨号适配器”设置了IP，结果造成他ping不通其他机器。 e.g.将拨号适配器设置ip=172.31.0.1 C:\>ipconfig/all Windows 98 IP Configuration Host Name . . . . . . . . . : R4U2L8 DNS Servers . . . . . . . . : Node Type . . . . . . . . . : Broadcast NetBIOS Scope ID. . . . . . : IP Routing Enabled. . . . . : No WINS Proxy Enabled. . . . . : No NetBIOS Resolution Uses DNS : No 0 Ethernet adapter : Description . . . . . . . . : PPP Adapter. Physical Address. . . . . . : 44-45-53-54-00-00 DHCP Enabled. . . . . . . . : No IP Address. . . . . . . . . : 172.31.0.1 Subnet Mask . . . . . . . . :
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