How a single misbehaving client can take down your network Well, not really your entire network but definitely DHCP. I came across a linux client that had issues with assigning an IP address using dhclient. The dhclient process would throw a null pointer exception during the phase in which it attempts to validate the assigned IP address. From here, dhclient sends a DHCPDECLINE message to the server. The DHCPDECLINE message tells the server that something is either wrong with the DHCP parameters or that the client discovered that the IP was in use (through gratuitous ARP or in this case, a failed attempt at sending a gratuitous ARP). cat /var/log/messages : RFC 1541 states: “If the server receives a DHCPDECLINE message, the client has discovered through some other means that the suggested network address is already in use. The server MUST mark the network address as “not allocated” and SHOULD notify the local system administrator of a possible configuration pr...
There are a number of possible causes for the failure of a server to boot into Windows. This article deals with a problem in the boot files and demonstrates how to repair them. Solution IMPORTANT: Drive Letters Change in WinRE When booting to the Windows Recovery Environment (WinRE), the drive letters are assigned on a first-come, first-serve basis. For example, the C: drive in Windows will often have a different letter in WinRE. The DiskPart utility can be used to keep track of the drives and what is stored on them. Restoring Boot Files Note: If there is no System Reserved partition. It is okay to select the drive containing the Windows folder . First Partition: 100 MB System Reserved (No drive letter) Second Partition: 60 GB (C:) OS Third Partition:1.5 TB (D:) Data DVD Drive: E: Note: The DVD drive’s letter changes from E: to F: in WinRE. Boot to the Windows Server DVD. Open the command prompt. Server 2008 R2 If no driver is needed, p...
Occasionally my storage goes offline, this can put VMware ESXi into a bit of a spin if your VM guests are hosted on the storage that went offline. The guests on the datastore will be greyed out with “(inaccessible)” next to them. There is a quick and easy way to fix this, by restarting the management service on the host(s) that the vm guests reside on. ( Run these commands without the “#” ). Shell or console onto the host #/etc/init.d/hostd restart exit Close the vsphere client Open the vsphere client This won’t take effect immediately (up to 5 minutes), but it will come back. You can check to see if the hostd service is running: #ps aux | grep hostd If that doesn’t work you can try and reboot your vCenter server or at the very least, restart the services on the vCenter server. If that doesn’t work you will have to migrate the guests off the physical host and restart the host. Obviously the latter is drastic so only perform that action should you have no other optio...
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