Loopback Interface??

Answered Question
Aug 2nd, 2010
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  Hi,


I want to know why do not have MAC address on loopback interface on Router or Switch??


If I see on useing #show int loopback 0


There is no MAC address.


If these are not support the MAC address then it's only depend on IP even on WAN area??


Please your helpful reply require..

Correct Answer by Richard Burts about 6 years 10 months ago

Encapsulation is how you build a header for a particular physical media. Since there is no physical media associated with a loopback interface there is no encapsulation associated with a loopback interface.


HTH


Rick

Correct Answer by Nagaraja Thanthry about 6 years 10 months ago

Hello,


Yes, the ping is via the IP addresses and IP routing. There is no

encapsulation required for that.


Regards,


NT

Correct Answer by Richard Burts about 6 years 10 months ago

Let us start the explanation by reviewing a fundamental concept about MAC address. The purpose of a MAC address is to distinguish individual devices on the media (it is a link local layer 2 address).
Since the loopback interface is by definition not connected on any physical media there is no purpose in a link local address and MAC addresses are not supported on loopback interfaces.


HTH


Rick

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Nagaraja Thanthry Mon, 08/02/2010 - 06:42
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Hello,


Loopback interfaces are virtual interfaces created in software by the router/switch. Unlike other virtual interfaces, the loopback interface will not have any physical connectivity with another device. Whoever needs to communicate with the loopback interface need to go through another physical interface enabled with IP routing. So, communication between that physical interface and the loopback interface happens in software (no need of MAC). Hence you do not need a MAC address for the loopback interface.


Hope this helps.


Regards,


NT

Correct Answer
Richard Burts Mon, 08/02/2010 - 11:03
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Let us start the explanation by reviewing a fundamental concept about MAC address. The purpose of a MAC address is to distinguish individual devices on the media (it is a link local layer 2 address).
Since the loopback interface is by definition not connected on any physical media there is no purpose in a link local address and MAC addresses are not supported on loopback interfaces.


HTH


Rick

abhi-adte Mon, 08/02/2010 - 20:35
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If Router A have loopback and Router B is can ping to loopback int. of Router A, so only on basis of IP address ping to same??


any idea abour encapsulation loopback??

Correct Answer
Nagaraja Thanthry Mon, 08/02/2010 - 20:40
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  • Cisco Employee,

Hello,


Yes, the ping is via the IP addresses and IP routing. There is no

encapsulation required for that.


Regards,


NT

Correct Answer
Richard Burts Tue, 08/03/2010 - 04:09
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Encapsulation is how you build a header for a particular physical media. Since there is no physical media associated with a loopback interface there is no encapsulation associated with a loopback interface.


HTH


Rick

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