Rockwell Automation 1783-BMxxx Stratix 5700 Ethernet Managed Switches User Manual - Manual (Page 139)

Rockwell Automation Publication 1783-UM004E-EN-P - June 2014 139
Manage the Switch via the Device Manager Web Interface Chapter 4
Reserve IP Addresses through DHCP Persistence
You can reserve and preassign an IP address from the IP address pool 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 require no
reconfiguration.
When the DHCP persistence feature is enabled, the switch acts as a DHCP
server for other devices on the same subnet, including devices connected to other
switches. If the switch receives a DHCP request, it responds with any unassigned
IP addresses in its pool. To prevent this from happening, check the Reserve Only
box on the DHCP window. This prevents the switch from responding when it
receives a request.
When DHCP persistence is enabled on a port and a DHCP request is made
from a connected device on that port, the switch assigns the IP address for that
port in the DHCP window. It also broadcasts the DHCP request to the
remainder of the network. If another DHCP server with available addresses is on
the network and receives this request, it can try and respond. This can override
the initial IP address assigned by the switch depending on how the end device
behaves (takes first IP address response or the last). To prevent the IP address
from being overridden, enable DHCP snooping on the appropriate VLAN.
Doing this blocks the broadcast of this DHCP request, so that no other server,
including another Stratix switch with DHCP persistence enabled, responds.
Ending IP 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…255.
Make sure that none of the IP address you assign are being used by other devices in your network.
This field is required.
Default Router The default router IP address for the DHCP client that uses this server. The format is a 32-bit numeric address written as four numbers
separated by periods. Each number can be from 0… 255.
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 Server 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…255.
CIP Instance A number from 1…15 to identify the address pool.
[Lease Length] The duration of the lease for an IP address that is assigned to a DHCP client. Click one of the following:
• Never Expires
• User Defined
If you click User Defined, enter the duration of the lease in the numbers of days, hours, and minutes. This lease length is used for all
assignments.
Field Description