Hi
There are really two types of loopbacks when you are talking about
routers...
1) Is a, virtual interface, for lack of a better term. They are often used
with advanced routing, i.e. OSPF, BGP4.
2) Is a physical loopback. This is used for testing lines and CPE (customer
premise equipment).
An example would be placing a serial interface on a router into lookback.
You would use this to test the line and equipment on the far side of loop.
You can loop quite a few of the pieces on a line, e.g. CSU/DSU this would be
used to test the "line" between the CSU/DSU and the router's interface, NIU
(network interface unit) you would use this to test the "line" between the
demarc (sp) and the interface on the router, if you have the help of the
telco, they can also create loops inside their network to aide in testing.
HTH
--
John Hardman, MCSE+I, CCNA
ArrisTech/CCS-IS SysAdmin
<[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> I was just wondering why you would waste a physical int. for a loopback?
You
> can create logical interfaces with the "int Loopback0" and so on. So why
> would you take up a serial int unless you were using subinterfaces? I'm
not
> trying to be smart. I really want to know what or why this would be used
> instead of logical int's. Thanks group.
>
> Mark Z. ~ CCNA (CCDA on Monday the 31st) :)
>
>
> In a message dated 27.07.00 18:29:46 Central Daylight Time,
[EMAIL PROTECTED]
> writes:
>
> << just to let you know that you can set a loopback on a Cisco router
from
> the
> router ?
>
> You must be in the priv mode not user mode to put the router in
loopback.
>
> Router#
> Router#conf ter ( hit enter )
> Router(config)#int s0 ( hit enter )
> Router(config-if)#LOOPBACK (hit enter )
> Router(config-if)#end (hit enter )
> Router#sho int s0 ( you will now see the serial interface in loopback)
>
> To remove the loopback from the serial interface just reload the router
or
> do this:
>
>
> Router#
> Router#conf ter ( hit enter )
> Router(config)#int s0 ( hit enter )
> Router(config-if)#NO LOOPBACK (hit enter )
> Router(config-if)#end (hit enter )
> Router#sho int s0 ( you will now see the serial interface out of the
> loopback)
>
>
>
> Brian
> Email Address [EMAIL PROTECTED] >>
>
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