Switch User Manual

44 An 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

5.1 27 August 2007