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CHAPTER22
Advanced DHCP Server Properties
This chapter describes how to set up some of the more advanced DHCP server properties. Before clients
can use DHCP for address assignment, you must add at least one scope to the server. This is described
in Chapter 19, “Configuring Scopes and Networks.” The additional properties are:
� Configuring BOOTP, page 22-1
� Defining Advanced Server Parameters, page 22-3
� Integrating Windows System Management Servers, page 22-7
� Using Extensions to Affect DHC
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Chapter 22 Advanced DHCP Server Properties Configuring BOOTP Every Network Registrar DHCP policy has attributes with which you can configure the information you want returned directly in the file, siaddr, or sname fields. The Network Registrar DHCP server also supports a configuration parameter with which you can configure the policy options and determine which of the file, sname, or siaddr values you want returned to the BOOTP device. Network Registrar supports an analogous configuratio
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Chapter 22 Advanced DHCP Server Properties Defining Advanced Server Parameters Moving or Decommissioning BOOTP Clients When you move or decommission a BOOTP client, you can re-use its lease. To decommission a BOOTP client, you must remove its lease reservation from the scope and force its lease to be available. Force the lease available in the local cluster Web UI, or set scope name removeReservation and lease ipaddr force-available in the CLI. Using Dynamic BOOTP When you use dynamic BOO
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Chapter 22 Advanced DHCP Server Properties Defining Advanced Server Parameters Table 22-1 DHCP Advanced Parameters Advanced Parameter Action Description max-dhcp-requests set/ Controls the number of buffers that the DHCP server allocates for unset receiving packets from DHCP clients and failover partners. If this setting is too large, a burst of DHCP activity can clog the server with requests that become stale before being processed. This results in an increasing processing load that ca
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Chapter 22 Advanced DHCP Server Properties Defining Advanced Server Parameters Table 22-1 DHCP Advanced Parameters (continued) Advanced Parameter Action Description max-dhcp-responses set/ Controls the number of response buffers that the DHCP server unset allocates for responding to DHCP clients and performing failover communication between DHCP partners. In a non-failover deployment, the default setting of twice the number of request buffers is sufficient. In a failover deployment, you
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Chapter 22 Advanced DHCP Server Properties Defining Advanced Server Parameters In the CLI, use dhcp show and dhcp get to show the current server parameters, then use dhcp set, dhcp unset, dhcp enable, and dhcp disable to change them (see Table 22-1). Step 2 In the Web UI, click the name of the server. Step 3 In the Web UI, add or modify attributes on the Edit DHCP Server page. Step 4 In the Web UI, click Modify Server to make the changes. Deferring Lease Extensions The defer-lease-extensio
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Chapter 22 Advanced DHCP Server Properties Integrating Windows System Management Servers As a complication, the server also keeps track of the time when it last heard from the client. Known as the last transaction time, sites sometimes use this information as a debugging aid. Maintaining this time robustly requires a write to the database on every client interaction. The last-transaction-time- granularity attribute is the one to set. (See the attribute description in Table 22-1 on page 22
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Chapter 22 Advanced DHCP Server Properties Using Extensions to Affect DHCP Server Behavior When you install the Microsoft BackOffice Resource Kit, the system path is not updated to reflect the location of the SMS data link library (DLL). Use one of these methods to configure this attribute: a. Set the sms-library-path attribute to a relative path: � First, modify the system PATH variable to append the path of the directory where the DLL is installed: sms-install-directory\diagnose � Then
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Chapter 22 Advanced DHCP Server Properties Using Extensions to Affect DHCP Server Behavior You can solve the problem of the two IP addresses by writing either of these extensions: � One that causes the DHCP server to drop the Token Ring (6) hardware type packet. � One that changes the Token Ring packet to an Internet packet and then switches it back again on exit. Although this extension would be more complex, the DHCP client could thereby use either return from the DHCP server. You can w
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Chapter 22 Advanced DHCP Server Properties Tuning the DHCP Server � Windows: – For Tcl—\program files\Network Registrar\extensions\dhcp\tcl – C or C++—\program files\Network Registrar\extensions\dhcp\dex It is best to place these extensions in the appropriate directory for TCL or C/C++ extensions. Then, when configuring the filename, just enter the filename itself, without slash (/) or backslash (\). If you want to place extensions in subdirectories, enter the filename with a path separato
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Chapter 22 Advanced DHCP Server Properties Tuning the DHCP Server Table 22-2 DHCP Log Settings (continued) Log Setting (Numeric Equivalent) Description client-detail (8) After every client-class client lookup operation, logs the composite of the data found for the client and its client-class. Useful when setting a client-class configuration and debugging problems in client-class processing. client-criteria-processing Logs whenever a scope is examined to find an available lease or to (9
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Chapter 22 Advanced DHCP Server Properties Configuring Virtual Private Networks and Subnet Allocation � Adjust the mcd-blobs-per-bulk-read attribute value to tune DHCP start and reload times. Generally, a higher mcd-blobs-per-bulk-read attribute value results in faster server start and reload times, at the cost of using more memory. Values can be set to any number between 1 and 2500 using the mcd-blobs-per-bulk-read DHCP server attribute. The current default is 256 blobs. � Consider sett
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Chapter 22 Advanced DHCP Server Properties Configuring Virtual Private Networks and Subnet Allocation � Querying subnet utilization (see the “Generating Subnet Utilization History Reports” section on page 8-13). � Querying lease history (see the “Running IP Lease Histories” section on page 21-16). If you do not configure a VPN, Network Registrar uses the global VPN of 0 on each scope. To configure a VPN whereby a client can request IP addresses from a DHCP server using a relay agent, you
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Chapter 22 Advanced DHCP Server Properties Configuring Virtual Private Networks and Subnet Allocation If the server-id-override suboption of the relay-agent-info option (82) exists, the DHCP server uses its value to compare to that of the dhcp-server-identifier option in the reply packet. Any packet that the DHCP client unicasts then goes directly to the relay agent and not to the server (which may, in fact, be inaccessible from the client). Both partners in a failover environment can re
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Chapter 22 Advanced DHCP Server Properties Configuring Virtual Private Networks and Subnet Allocation Step 3 Specify the appropriate VPN identifier, either by VPN ID or VRF name. It is rarely both. � If you use a VPN ID, set the vpn-id attribute value for the VPN. The value is usually in hexadecimal, in the form oui:index, per IETF RFC 2685. It consists of a three-octet VPN Organizationally Unique Identifier (OUI) that corresponds to the VPN owner or ISP, followed by a colon. It is then f
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Chapter 22 Advanced DHCP Server Properties Configuring Virtual Private Networks and Subnet Allocation VPN Usage The VPN name is used to qualify many DHCP objects in Network Registrar, such as IP addresses (leases), scopes, and subnets. For example, lease names can have this syntax: vpn/ipaddress For example, red/192.168.40.0 A VPN can be any unique text string except the reserved words global and all. You can use global and all when you export address or lease data. The global VPN maps t
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Chapter 22 Advanced DHCP Server Properties Configuring Virtual Private Networks and Subnet Allocation In the CLI—To import leases, use import leases filename. Each lease entry in the file can include the VPN at the end of the line. If it is missing, Network Registrar assigns the [none] VPN. (See also the “Importing and Exporting Lease Data” section on page 21-3.) nrcmd> import leases leaseimport.txt To export the address or lease data to include the VPN, use export addresses with the vpn
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Chapter 22 Advanced DHCP Server Properties Configuring Virtual Private Networks and Subnet Allocation Step 1 Create a DHCP address block for a subnet, set the initial subnet mask and its increment, and set other subnet allocation request attributes. Also, associate a policy or define an embedded policy. � If you use VPNs, you can specify a vpn or vpn-id attribute (see the “Configuring Virtual Private Networks Using DHCP” section on page 22-12). Note Unsetting the VPN ID in the CLI reverts
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Chapter 22 Advanced DHCP Server Properties Setting DHCP Forwarding VPN and Subnet Allocation Tuning Parameters Consider these tuning parameters for VPNs and on-demand address pools. � Keep orphaned leases that have nonexistent VPNs—Network Registrar usually maintains leases that do not have an associated VPN in Network Registrar’s state database. You can change this by enabling the DHCP attribute delete-orphaned-leases. The server maintains a lease state database that associates clients
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Chapter 22 Advanced DHCP Server Properties Setting DHCP Forwarding As the DHCP server processes these scripts, it checks the environment dictionary for this string: cnr-forward-dhcp-request 3. When it finds that string and it has the value true (enabled), the server calls its forwarding code. 4. The forwarding code checks the environment dictionary for a string with this key: cnr-request-forward-address-list It expects a list of comma-separated IP addresses with an optional colon-delimite
