loop back never goes down, helps maintaining adjacency of routers if used with routing protocols
(config)#no interface loopback x
The main advantage of running a loop back interface with OSPF enabled on the router is that there is minimal cost. The IP address will also remain stable in this set up.
Configure the router ID on both routers. Configure the R2 router interfaces for area 0. Configure a loopback interface on both routers. Configure the proper subnet masks on the router interfaces.
Outbound interface
The highest MAC address among the active interfaces of the network will be used. There will be no router ID until a loopback interface is configured. The highest IP address among the active FastEthernet interfaces that are running OSPF will be used. The highest IP address among the active interfaces will be used.
it should be on back of router!
The router ID is used to uniquely identify each router in the OSPF routing domain.If no loopback interfaces are configured, the router chooses the highest active IP address of any of its physical interfaces.
A(config)# router rip A(config-router)# passive-interface S0/0 B(config)# router rip B(config-router)# network 192.168.25.48 B(config-router)# network 192.168.25.64 A(config)# router rip A(config-router)# no network 192.168.25.32 B(config)# router rip B(config-router)# passive-interface S0/0 A(config)# no router rip
AUI
If a router has a route in its routing table, it will have a next hop IP address and / or outbound interface. If a router does not have a route in its routing table the packet will be dropped.
The command ip classless is enabled on the router.
Router(config-if)#