Cisco CCNA Exam Tutorial: Loopback Interfaces

As a CCNA prospect, you probably possess some background in PC hardware and workstation support. You are already knowledgeable about loopback interfaces, especially 127.0.0.1, the loopback address given to a PC, If so.

There’s one logical interface you need to know about, and that’s – you got it – when you are learning all about different physical interfaces for the CCNA assessment – serial, ethernet, and BRI, among others! – the loopback interface.

we use loopback interfaces on routers and switches to start with what is much less instantly obvious is. Many of the Cisco router features that can use loopbacks are intermediate and advanced features that you’ll understand in your CCNP and CCIE reports, but these features all return to one fundamental concept: If the loopback interface on a is down, that means the router is unavailable in general.

In comparison, a interface being down does not mean the router itself has gone out of commission. A router’s ethernet interface could decrease, nevertheless the other physical interfaces on that router remain working. There is nothing physical that will go wrong with it, since a loopback interface is rational.

As I stated, you’ll learn different Cisco router and switch functions that utilize loopback interfaces as you climb the Cisco certification ladder. There’s one myth about Cisco loopback interfaces that you would like to get clear on today, though. Youre probably acquainted with loopback interfaces on a PC, and may even know that the target selection 127.0.0.0 is reserved for loopback addressing.

Remember that this reserved handle range does not apply to loopbacks on Cisco devices, nevertheless. If you make an effort to assign an address from this variety to a Cisco loopback interface, you get this result:

R1#conf t

Enter configuration commands, one per line. End with CNTL/Z.

R1( config )#interface loopback0

R1( config-if )#ip handle 127.0.0.2 255.255.255.0

Not just a valid host address – 127.0.0.2

R1( config-if )#ip address 127.1.1.1 255.255.255.0

Not a legitimate host address – 127.1.1.1

The range 127.0.0.0 is reserved for host loopbacks (such as PCs), not hubs or switches. The most commonly used target from this range is 127.0.0.1 if you cant ping that on a, that means you cant ping your self, which means theres a problem with the TCP/IP mount itself.

Hold these facts in your mind on the exam and at work, and youre on the right path to CCNA exam success!

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