【School】 upgrade the switch causes the weak can not get IP-address (to) --- Power By 【China】 weak home network.

<br> <BR> recently decided to upgrade network equipment unit, the original 3Com switches are used, all the computers are classified into two VLAN, except for some computer a fixed IP, the other computers are received by a DHCP server .address. .After the implementation of network upgrades, network-centric routers the same, most of the access-level switches to replace Cisco Catayst 3550 or Cisco Catayst 2950, but after upgrading the following: some start or restart the computer just can not get IP address, but in the manual .Set IP address and then receive. .Through observation, I found that only a computer with Windows 98 before that happens, I believe that the computer may be infected with a virus specifically for Windows 98, but were not detected by Norton and Kingsoft virus, so we ruled out the virus .reasons. .Is it a problem with DHCP server, DHCP server, check again to confirm DHCP server is running properly. .After careful observation, I found that only Cisco switches connected to a computer using Windows 98 similar problems, and use Windows 2000 or Windows XP computer has no problems, but when using 3Com switches, the use of computers are Windows 98 .work properly. .I selected a Cisco Catayst3550-48 switch, carefully check its configuration, ARP table, Mac-Add table and the Log, found no abnormalities. .I thought of using a computer is not Windows 98 can not obtain IP address, but not available at boot time, then, may be in the switch port initialization problems. .Cisco switch port is not connected to the computer in the forwarding state immediately, and it has a from Bloking (blocking), Listening (listening), Learning (Learning) to Forwarding (forward) state transition process. .So, most likely is in the process, Cisco switches and Windows 98 network initialization conflict. .If the Cisco switch to change the port forwarding, that is, the port once it power to in the forwarding state should be able to solve the problem. .So the author in the port configuration Cisco Catayst 3550 added configure statement "spanning-tree portfast" after solving the problem. .It seems, Windows 98 network boot process does the Spanning Tree Protocol, and Cisco switches, there is a conflict, but only in the case of using DHCP will be shown, but the "spanning-tree portfast" command can only be used for the switch port directly connected to the computer .case, if the port cascade of other switches, this command will run spanning tree protocol error. .In this case, the general does not require additional configuration, because the default Spanning Tree Protocol is enabled on the Cisco switch, of course, in the Cisco access layer switch port with "spanning-tree uplinkfast" command to reduce its .convergence speed. .<BR>.