Re: OT: Loopback usages

Hi Tharak,

Loopback interfaces serve a number of purposes.

One reason they exist is for network management - when more than one
physical interface is used to reach a destination. For example, within a
mesh, or where the router has an interface for backup purposes (such as
DSL or 3G).
Consider this, the network management system will generally have a
single IP address configured to poll the device. If a physical interface
is used, and one of the other interfaces goes down you can still manage
the device. However, if the physical interface goes down then not only
do you lose status of the device, you usually lose access as well.
When a loopback interface is used for management purposes, it is always
up, and depending on how your network is configured, will be reachable
through a number of paths (and physical interfaces). If the best path
goes down, it no longer affects the reporting or reachability of the
device as a different path is chosen to reach the loopback address.

Another reason is to reduce convergence times when using dynamic routing
protocols, again as the loopback interface is always up, the loss of one
physical interface and the removal of its network from the routing table
will not cause the routing process (or multiple routing processes) to
re-converge, or worst case cause a new OSPF DR/BDR election to take
place. This can happen, however, when using a physical interface IP address.

regards Andy

Abraham, Tharak wrote:
> Thanks Richard and Keegan !
>
> Your point are valid, it has a little part played in almost every
> protocol/technology/services.
>
> Thinking of a router without loopback..will give the answer i guess..-:)
>
> Best Regards,
> Tharak Abraham Luke
>
>
> On Wed, Aug 5, 2009 at 2:56 AM, <Keegan.Holley_at_sungard.com> wrote:
>
>
>> I would say they are just there. They don't necessarily "do" anything.
>> It's just a logical interface. It's there to help you "do" things, not to
>> do things itself. You'll never list all of the uses for a loopback (in or
>> out of the classroom). I think the best definition would be a simple one.
>> Like "An interface that belongs to the router itself and not any particular
>> network.". Then list the popular uses. Router-id's, nat's, tunnels,
>> syslog, snmp...
>>
>> Have fun,
>>
>> Keegan
>>
>>
>>
>> From: "Abraham, Tharak" <tharakabraham_at_gmail.com>
>> To: Cisco certification <ccielab_at_groupstudy.com> Date: 08/04/2009 04:24 PM
>> Subject: OT: Loopback usages Sent by: nobody_at_groupstudy.com
>> ------------------------------
>>
>>
>>
>> Hi All,
>>
>> While giving some short lectures on CCNA, my colleague asked me ..
>>
>> What are these loopbacks interfaces doing in Routers ?
>>
>> I tried my best...
>> Stability for protocol functionality, BGP, OSPF blah blah..but it didnt
>> make
>> sense giving those examples..-:)
>> Avoiding situations when/if physical interfaces go down...but then..
>> Populating networks ..?
>>
>> I was not happy..:-(
>>
>> Is that all folks ?
>>
>>
>> Best Regards,
>> Tharak Abraham Luke
>>
>>
>> Blogs and organic groups at
>> http://www.ccie.net
>>
>>
>> _______________________________________________________________________
>> Subscription information may be found at:
>> http://www.groupstudy.com/list/CCIELab.html
>>
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html

Blogs and organic groups at http://www.ccie.net
Received on Wed Aug 05 2009 - 19:05:03 ART