Rockwell Automation Publication 1783-UM003G-EN-P - December 2012 75
Manage the Switch via the Device Manager Web Interface Chapter 3
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 (including other Stratix 8000 switches). If the switch receives a DHCP
request it will respond with any unassigned IP addresses in its pool. To prevent
this from happening, check the Reserve Only box on the DHCP dialog box. This
ensures that the switch will not respond when a request is received.
When the DHCP persistence feature 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 dialog box. It will also broadcast 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 may try and respond. This may
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 8000 or Stratix 8300 switch with DHCP
persistence enabled) will respond.
If you are using DHCP persistence, we recommend that you initially assign static
IP addresses to end devices. If an end device fails and is replaced, the DHCP
persistence feature assigns an IP address from the DHCP persistence table. The
device will function properly with this IP address, but you should reassign a static
IP address to the replaced devices.
To Next Page
Loading...
Need help?
General
