Nortel Networks NN47200-503 manual Avoiding duplicate IP addresses, Automatic router ID change

44An Introduction to IP Routing Protocols

DHCP relay uses a hardware resource that is shared by switch Quality of Service applications. When DHCP relay is enabled globally, the Quality of Service filter manager will not be able to use precedence 11 for configurations. For the filter manager to be able to use this resource, DHCP relay must be disabled for the entire unit or stack.

Avoiding duplicate IP addresses

The Nortel Ethernet Routing Switch 5500 Series has built-in safeguards to avoid issuing duplicate IP addresses, because the switch functions as a stack as well as a stand-alone system. These safeguards apply to stack configuration changes (for example, when a stack is forming or after a unit is removed from a stack).

The system allows the use of an existing IP address under the following conditions:

•When a unit leaves a stack:

—If the unit was the acting Base Unit (BU) of the stack and the stack consisted of only two units.

—If the IP blocking mode in the stack was set to none.

•When a unit boots up:

—If the unit was never in a stack.

—If IP blocking was manually turned off prior to the current boot.

—If the unit was the designated Base Unit (BU); that is, selected by hardware switch on the unit, either on the back or on the UI button on the front; and the stack consisted of only two units.

—If the IP blocking mode was set to none.

If the desired switch IP address is blocked by the system, then the address must be configured manually in the command line interface.

Automatic router ID change

If a unit leaves the stack and becomes standalone (when the stack disjoins), the router ID is automatically changed to its default value. This prevents router ID duplication in the OSPF routing domain.

Prerequisites: IP blocking must be turned off (set to none) and OSPF must be globally enabled.

TIP: The change in router ID is temporary (not saved in non-volatile random access memory) and, upon reset, the router ID is restored.

Nortel Ethernet Routing Switch 5500 Series

Configuration-IP Routing Protocols

NN47200-503 03.01 Standard

5.127 August 2007

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