Switch User Manual

IP routing 45

IP blocking

IP Blocking is a Layer 3 feature of the Nortel Ethernet Routing Switch

5500 Ser ies that provides built-in safeguards for the usage of duplicate IP

addresses in a stacked environment. IP Blocking is used whenever a unit

leaves a stack or is rebooting inside the context of a stack. Depending on

the setting in use, Layer 3 functionality is either continued or blocked by

this feature.

IP Blocking can exist in either a none or full condition. When IP Blocking

is set to none, duplicate IP addresses are permitted in the stack

unconditionally. When the full condition is set, duplicate IP addresses are

blocked in the stack unconditionally.

In a stack environment, Nortel recommends that IP blocking mode none be

used in a stack of 2 units. In such a stack environment and IP blocking

mode combination, the following functional characteristics can be expected:

•

If the stack base unit becomes non-operational the following will occur:

— Layer 3 functionality will continue to run on the non-base unit.

— Dynamic routing protocols still run on the non-base unit.

•

If the stack non-base unit becomes non-operational the following will

occur:

— Layer 3 functionality will continue to run on the base unit.

— Dynamic routing protocols run on the base unit.

A disadvantage of this conﬁguration is that if the non-operational unit does

not rejoin the stack, address duplication will occur.

In stack environments of more than 2 units, Nortel recommends using IP

blocking mode full. In such a stack environment and IP blocking mode

combination, the following functional characteristics can be expected:

• If the stack base unit becomes non-operational the following will occur:

— The temporary base unit takes over base unit duties.

— The temporary base unit runs the Layer 3 and DRP functionality.

— The takeover of the temporary base unit will cause the MAC

addresses of the Layer 3 interfaces to change and the MAC

addresses from the temporary base unit MAC address pool are

used. This may cause a minor disruption in routing trafﬁc. To

facilitate quick failover in this instance, gratuitous ARP messages are

sent out for each interface for 5 minutes at 15 second intervals.

•

If a stack non-base unit becomes non-operational the following will

occur:

Nortel Ethernet Routing Switch 5500 Series

Conﬁguration-IP Routing Protocols

NN47200-503 03.01 Standard

5.1 27 August 2007