Managing DHCP Server
Posted on Tuesday, October 13, 2009
This article was posted in Microsoft
- To change the DHCP server status open the DHCP console, go to actions menu and select one of Start, Stop, Pause, Restart and Resume
- You can also use the Net command to change the status of DHCP server, the command line syntax is Net [operation like start/stop/pause/continue] DHCP_server
- You can manage DHCP server from command line using netsh command line tool, with dhcp subcommand option.
- Superscope is an administrative grouping of scopes that is used to support multiple logical subnets also known as multinets on a single network segment. They exist on 1 physical network and work with multiple logical networks. This method is used for DHCP server to provide clients with addresses from multiple scopes. Administrator needs to delete the superscope before deleting any scope that is contained within it. Superscopes group scopes that can be activated together, it doesn’t carry any details about the scopes.
- To move a scope to a new addressing range first create a new scope with new range and then activate it and deactivate the old scope. Either manually or by waiting make sure all clients move to the new scope, delete old scope.
- If a superscope is not defined on a server then only one scope can be active at a time.
- In order for the DHCP server to not assign already assigned IP address to a new client DHCP has conflict detection (advanced tab of DHCP server properties) in which the server pings the address it is about to assign in order to check whatever it is free.
- Multicast scope – regular DHCP scopes to provide client configurations by allocating ranges of IP addresses from the standard classes (A, B, or C). The multicast address range uses an extra address class, D, IP addresses from 224.0.0.0 to 239.255.255.255 for use in IP multicasting. In every TCP/IP network, each host is gets own IP address, from regular address classes. The unicast IP address is assigned before host can support and use secondary IP addresses, such as a multicast IP address. Multiple PCs can share the same multicast IP address. On private networks it is recommended to start with 239.192.0.0 range. When a packet is sent with destination that is a multicast address it gets delivered to all PCs that have it. Multicast scopes are supported through the use of MADCAP (Multicast Address Dynamic Client Allocation Protocol).
- DHCP server performs backup by itself up every 60 minutes, you can also do manual backup. Manual backup is performed from Backup command in the DHCP console. When the backup is made the whole DHCP database is saved. Some things, like credentials are not saved. The manual backup default location is %systemroot%\system32\dhcp\backup. The following data is backed up: all scope information including superscopes and multicast scopes, reservations, leases, all options. The database backup file is called DHCP.mdb.
- To change backup behaviour of DHCP server, one needs to edit the following registry keys:
- HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DHCPServer\Parameters\BackupInterval\
- HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DHCPServer\Parameters\BackupDatabasePath\
- To migrate DHCP server all you need to do is move the database, simply back it up and then restore it on the new computer
- Jetpack.exe is a tool that allows support for offline compaction and repair of Jet databases such as DHCP or WINS. You can use dynamic compacting of DHCP server database without the need to bring server offline, but offline defragmentation is more efficient. Compacting should be done whenever the database size grows beyond 30 Mb or you get corruption errors.
- Option class – they way DHCP server manage provided to clients within a scope. When an option class is added, clients of that class can get class specific configuration options. There are two types of classes, Vendor classes and User classes.
- Vendor class is used to assign vendor specific options to clients that share common vendor
- User class is used to assign options to clients that share user defined similarities
- The DHCP server has a default user class called ‘Default routing and remote access‘. Options in this class apply only to clients that request address while connecting through Routing and Remote access. You can set different options, for example you can assign shorter leases to the clients connected remotely (this is option number 051 Lease).
- To create your own user or vendor class open DHCP console and r-click the DHCP server and select ‘Define User classes’. After defining a new class you need to assign ID to it and options. On the client side you need to make sure that the clients know in what class they are, you do this by executing ipconfig /setclassid. To view all classes allowed by the DHCP server execute ipconfig /showclassid