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Webcast-Catalyst9k
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The need of Loopback0 Interface on A Router !!!

Hi anyone plsease help to clarify the following;

RouterA;

Loopback0 - 10.0.1.10 255.0.0.0

e0/0 - 10.0.2.1 255.0.0.0

bri0/0 - no ip address

dialer1 - ip numbered loopback0

Questions;

(1) When do we need the loopback address on a router ?

(2) If the above RouterA dials to another RouterB, what is the role of loopback address here ?

(3) If the RouterB also has a loopback address, does it needs to be in the same subnet of loopback address of RouterA ?

(4) Is loopback address related to static IP route ?

Please help

2 REPLIES

Re: The need of Loopback0 Interface on A Router !!!

1) If you want to change your router ID (example for OSPF) but you can't renumber a physical interface. It is also good for peering in BGP and DLSW+, as the interface never goes down (unless you admin down it), and if your peer has multiple paths to you, they peer with the loopback so that if one path dies, you are still peered. They can also be used in almost any situation you want if you always want the interface to be up (eg Ipsec tunnel).

2) The dialer interface borrows the loopback's address. Packets are sent with a source IP of the loopback, and the loopback is routerb's next hop.

3)No, the loopback on routerb would have to be on a different subnet or you have routing problems. Ip unnumbered requires both ends of the link to be unnumbered though.

4) Not sure what you are getting at but, No they are not related.

Hope it helps.

Steve

Gold

Re: The need of Loopback0 Interface on A Router !!!

Loopbacks are very useful for things like:

OSPF router ID's

DLSW, and VPN Peers

GRE tunnels.

Think of it as an interface that never fails, unless the router dies.

2. In your case, the dialer profile is borrowing the loopback address,

thats acceptable.

3. I could as a target for the route statement, its always there.

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