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Passive-interface

Hi ,

Can someone tell me...how does Passive-Interface work in OSPF & EIGRP with example           

  • LAN Switching and Routing
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2 REPLIES
Hall of Fame Super Silver

Re: Passive-interface

Hello Sivakanth,

passive interface combined with network  ( for EIGRP) and with network .. area ( for OSPF) allow to advertise the IP subnet associated to the involved interface as an internal route ( for EIGRP and for OSPF) without building neighborships on it.

A typical example is a campus network with 20 client vlans - 20 IP subnets served by two multilayer switches SW1 and SW2.

The IP subnets associated to these client vlans have to be advertised in the IGP in order to allow return traffic to client PCs from everywhere.

If we simply use the network ( for EIGRP) or network area command ( for OSPF) we achieve the advertisement but the price to pay is that SW1 and SW2 become neighbors in all 20 client Vlans. This is clearly a waste of resources as SW1 and SW2 are already interconnected by other means.

An alternative could be the use of redistribute connected eventually with a route filter implemented with a route-map.

However, redistributing connected creates external routes and this is specially important with OSPF: external routes are placed into LSA 5 type 2 or type 1 and they cannot be filtered at area boundary.

Hope to help

Giuseppe

New Member

Re: Passive-interface

Hello Giuseppe,

Thanks for quick response,

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