tcpdump -n -e -i eth2 ether src FC:99:47:49:D4:9E or ether dst FC:99:47:49:D4:9E
但是,当我将计算机引导到已安装的操作系统(在本例中为Windows Server 2012)并为DHCP配置该网络接口时,它会从DHCP服务器获取IP地址.如果我让tcpdump运行,我会看到以下内容：
13:34:36.525646 fc:99:47:49:d4:9e > ff:ff:ff:ff:ff:ff,ethertype IPv4 (0x0800),length 126: 169.254.239.3.54275 > 255.255.255.255.111: UDP,length 84 13:34:40.118071 fc:99:47:49:d4:9e > ff:ff:ff:ff:ff:ff,length 110: 169.254.239.3.137 > 169.254.255.255.137: NBT UDP PACKET(137): REGISTRATION; REQUEST; BROADCAST 13:34:40.888206 fc:99:47:49:d4:9e > ff:ff:ff:ff:ff:ff,length 110: 169.254.239.3.137 > 169.254.255.255.137: NBT UDP PACKET(137): REGISTRATION; REQUEST; BROADCAST 13:34:40.975407 fc:99:47:49:d4:9e > 01:00:5e:00:00:fc,length 66: 169.254.239.3.55524 > 224.0.0.252.5355: UDP,length 24 13:34:41.387736 fc:99:47:49:d4:9e > 01:00:5e:00:00:fc,length 24 13:34:41.418849 fc:99:47:49:d4:9e > ff:ff:ff:ff:ff:ff,length 358: 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP,Request from fc:99:47:49:d4:9e,length 316 13:34:41.419144 60:73:5c:68:b4:b6 > fc:99:47:49:d4:9e,length 342: 10.10.0.131.67 > 10.10.0.151.68: BOOTP/DHCP,Reply,length 300
什么可能导致DHCP在PXE引导过程中失败,同时在引入操作系统时成功？据我所知,PXE使用的是与Windows相同的网络接口.至少,PXE启动期间报告的MAC地址与Windows启动时通过DHCP获取IP的MAC地址相同.
The other time you may see this issue is with Pre-Boot Execution (PXE)
devices,such as Windows Deployment Services. The following figure
shows a typical PXE implementation. Here is what happens with PXE:You apply power to your computer,which activates the NIC,but less
than five seconds later,the computer’s POST finishes and the NIC
attempts to get an IP address from DHCP so that it can load a boot
image directly from the PXE server,which fails.The computer attempts to get an IP address from a DHCP server several
times within approximately 10 seconds,after which it gives up and
moves onto another boot device,such as the hard drive. The
unfortunate part of this process is that because it fails to get an IP
address or connect with the PXE server,you are not able to install
your new operating system image on that computer.The problem with this scenario is that because STP makes the computer
wait 45 seconds prior to forwarding traffic on the port,the PXE
network boot has timed out. image0.jpg PortFast is the solution to
this problem of delays when client computers are connecting to
switches. PortFast is not enabled by default. With PortFast enabled on
a port,you effectively take the port and tell spanning tree not to
implement STP on that port.This solution is not a bad one if only one computer is plugged into
the port — so that people will not be creating accidental loops on the
network,which can be frighteningly easy to do.
http://www.dummies.com/how-to/content/spanning-tree-protocol-stp-and-portfast.html
