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BAD_ADDRESS FLOOD IN WINDOWS DHCP SERVER

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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...
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Some Useful Storage Commands

Command to view all LUNs presented to a host #esxcfg-scsidevs -c And to check about a specific LUN, #esxcfg-scsidevs -c | grep  naa.id To find the unique identifier of the LUN,  you may run this command: # esxcfg-scsidevs -m To find associated datastore using a LUN id #esxcfg-scsidevs -m|grep  naa.id To get a list of RDM disks, you may run following command , #find /vmfs/volumes/ -type f -name ‘*.vmdk’ -size -1024k -exec grep -l ‘^createType=.*RawDeviceMap’ {} \; > /Datastore123/ rdmsluns.txt   This command will save the list of all RDM disk to a text file  rdmluns.txt  and save it to Datastore123. Now Run following command to find the associated LUNs, #for i in `cat /tmp/ rdmsluns.txt `; do vmkfstools -q $i; done This command will give you the  vml.id  of rdm luns, Now use following cmd to map  vml.id  to  naa.id #ls -luth /dev/disks/ |grep  vml.id     in output of t...
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How to fix “inaccessible” virtual machines in VMware ESX

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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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