dhcp

| DHCP
Why Use DHCP: What is DHCP What is DHCP persistence Procedures: Enable DHCP server mode and display DHCP IP address pools Enable global DHCP snooping DHCP server settings Create a DHCP IP address pool Modify a DHCP IP address pool Delete a DHCP IP address pool Display DHCP persistent IP addresses Assign a switch port IP address Change the switch port IP address Delete the switch port IP address Tips on Using this Window: Click the column headings to sort information. Click Submit to save your changes. Click Cancel to discard unsaved changes. Back to the top ### What Is DHCP Every device in an IP-based network must have a unique IP address. The Dynamic Host Configuration Protocol (DHCP) automatically assigns IP address information to newly connected devices (DHCP clients) in the network. If a device leaves and then re-joins the network, the device receives the next available IP address, which might or might not be the same address that it had before. DHCP prevents many problems caused by manual IP address misconfigurations and conserves IP address space. The switch can be set to operate as a DHCP server. A DHCP server assigns and manages a pool (or range) of available IP addresses on the switch or on a default router. Back to the top ### What Is DHCP Persistence The switch supports DHCP persistence. You can reserve and preassign an IP address to a specific switch port, so that a device connected to that switch port always receives the same IP address regardless of its MAC address. DHCP persistence is useful in networks that are set up in advance, where dependencies on the exact IP addresses of some devices exist. Use DHCP persistence when the attached device has a specific role to play and when other devices know its IP address. If the device is replaced, the replacement device is assigned the same IP address, and the other devices in the network are not reconfigured. Back to the top ### Enable DHCP Server Mode and Display DHCP IP Address Pools By default, the switch is not enabled to operate in DHCP server mode (the Enable DHCP check box is not selected). Deselect the check box if you do not want the switch to automatically assign IP information to connected devices. The DHCP Server tab displays this information.
Pool Name | The name of the DHCP IP address pool configured on the switch. A DHCP IP address pool is a pool (or range) of available IP addresses that the switch can assign to connected devices.
Interface | The VLAN associated with the subnet specified for the DHCP IP address pool. The VLAN is automatically chosen based on the given subnet. If the pool address is not associated with the given VLAN, no VLAN is displayed.
Reserved Only | This option reserves the address pool to only devices that are directly connected to the switch and assigned in the persistence table. With Reserved Only enabled, if a device is connected to a port which is not defined in the persistence table an address will not be assigned. DHCP requests from devices indirectly connected to the switch are ignored. This does not eliminate the ability for other DHCP servers on the network to assign addresses to devices connected to this switch. With Reserved Only disabled, if you connect a device to a port the device will received the next available address from the pool. By default, this option is disabled (the Reserved Only check box is not selected).
DHCP Snooping | DHCP snooping restricts broadcast of DHCP requests beyond the connected switch. This means that devices will only receive address assignments from the connected switch. This option is available only on VLAN interfaces. By default, this option is enabled (the DHCP Snooping check box is selected) on each VLAN interface.
Back to the top ### Enable Global DHCP Snooping By default, DHCP snooping is enabled (the Enable DHCP Snooping check box is selected) on all VLAN interfaces. Deselect the check box if you do not want DHCP snooping on all VLAN interfaces. Back to the top ### Create a DHCP IP Address Pool Select the DHCP Server tab from the DHCP window. Click Create from the DHCP Server tab. Enter information for the required and optional DHCP server settings. Click Done. Back to the top ### Modify a DHCP IP Address Pool Select the check box for the pool. Click Modify. Enter information for the required and optional DHCP server settings. You cannot modify the name of the pool. Click Done. Back to the top ### Delete a DHCP IP Address Pool Select the check box for the pool. Click Delete. Back to the top ### DHCP Server Settings
DHCP Pool Name | The name of the DHCP IP address pool configured on the switch. The name can have up to 31 alphanumeric characters. The name cannot contain a ? or a tab. This field is required. A DHCP IP address pool is a range (or pool) of available IP addresses that the switch can assign to connected devices.
DHCP Pool Network | The subnetwork IP address of the DHCP IP address pool. The format is a 32-bit numeric address written as four numbers separated by periods. Each number can be from 0 to 255. This field is required.
Subnet Mask | The network address that identifies the subnetwork (subnet) of the DHCP IP address pool. Subnets segment the devices in a network into smaller groups. The default is 255.255.255.0. This field is required.
Starting IP Address | The starting IP address that defines the range of addresses in the DHCP IP address pool. The format is a 32-bit numeric address written as four numbers separated by periods. Each number can be from 0 to 255. Make sure that the IP address that you assign is not being used by another device in your network. This field is required.
Ending IP Address | The ending IP address that defines the range of addresses in the DHCP IP address pool. The format is a 32-bit numeric address written as four numbers separated by periods. Each number can be from 0 to 255. Make sure that the IP address you assign is not being used by another device in your network. This field is required.
Default Router | The default router IP address for the DHCP client. The format is a 32-bit numeric address written as four numbers separated by periods. Each number can be from 0 to 255. This field is required.
Domain Name | The domain name for the DHCP client. The name can have up to 31 alphanumeric characters. The name cannot contain a ? or a tab.
DNS Server1 and 2 | The IP addresses of the Domain Name System (DNS) IP servers available to a DHCP client. The format is a 32-bit numeric address written as four numbers separated by periods. Each number can be from 0 to 255.
WINS Server1 and 2 | The IP addresses of the primary and secondary Microsoft NetBIOS name servers (WINS servers) available to a DHCP client. The format is a 32-bit numeric address written as four numbers separated by periods. Each number can be from 0 to 255.
CIP Instance | The CIP instance associated with a DHCP IP address pool. Each pool has its own CIP instance value. The first available CIP instance value is automatically assigned when the DHCP IP address pool is created. The value will be from 1 to 15.You cannot change the value.
Lease Length | The duration of the lease for an IP address that is assigned to a DHCP client. Click either: Never Expires User Defined If you click User Defined, enter the duration of the lease in the numbers of days, hours, and minutes.
Back to the top ### Display DHCP Persistent IP Addresses The DHCP Server tab on the DHCP window displays this information.
Interface | The number of the switch port, including port type (such as Fa for Fast Ethernet and Gi for Gigabit Ethernet), the base switch or the switch expansion module number (1, 2, or 3), and the specific port number. For example: Fa1/1 is Fast Ethernet port 1 on the base switch. Fa2/1 is Fast Ethernet port 1 on the first switch expansion module. Fa3/1 is Fast Ethernet port 1 on the second switch expansion module.
Pool Name | The name of the DHCP IP address pool configured on the switch.
IP Address | The IP address assigned to the switch port. The IP address must be from within the associated pool.
Back to the top ### Assign an IP Address to a Switch Port Select the DHCP Persistence tab from the DHCP window. Click Create on the DHCP Persistence tab. Select the switch port. Select the DHCP IP address pool in which the IP address exists. Enter the specific IP address. The format is a 32-bit numeric address written as four numbers separated by periods. Each number can be from 0 to 255. Click Done. Back to the top ### Change the IP Address of a Switch Port Select the check box for the switch port. Click Modify. Select the DHCP IP address pool in which the IP address exists. Enter the specific IP address. The format is a 32-bit numeric address written as four numbers separated by periods. Each number can be from 0 to 255. Click Done. Back to the top ### Delete the IP Address of a Switch Port Select the check box for the switch port. Click Delete. Back to the top