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Multiple Interfaces to a Link

Michael BarnesCisco Systems, Inc.

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Multiple Interfaces to a Link

● Specified in RFC2740● Too ambiguous

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Multiple Interfaces to a Link

● Each of the multiple interfaces are assigned different Interface IDs, used to detect MIL.

● If an interface has multiple instance IDs, it will be grouped with other interfaces based on matching instance Ids.

● Disable sending and receiving of OSPF packets on all but one of the interfaces to the link, except to receive self originated hellos

● Interface which continues to send and receive OSPF packets called the Active Interface

● Interfaces which do not send and receive OSPF packets called Standby Interfaces

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Multiple Interfaces to a Link

● All of the multiple interfaces to the link will however appear in the router-LSA

● Any link-local scope LSAs which are originated for a Standby Interface will be flooded over the Active Interface

● Prefixes on Standby Interfaces will be processed the same way as prefixes on the Active Interface

● If the Active Interface fails, another will have to take over, reforming all neighbor adjacencies from scratch

● All of the multiple interfaces to the link of adjacent router-LSAs must be found and used in the next-hop calculation

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Multiple Interfaces to a Link

● Standby state is added to the Interface finite state machine

● Events added to the Interface FSM– MultipleInterfacesToLink– ActiveInterfaceDead