You define a loopback interface using the global configuration mode command:
int loopback 0
It immediately creates a virtual interface which is by default in the up/up
state. This interface does not depend on other things ( like keepalives,
clocking, physical cable connectivity ) to remain in the up/up state and
remains up as long as the router is up and running.
Take OSPF for example. In order for OSPF to function properly it requires a
Router ID which is the highest IP address of an active interface on the
router. In case you have loopback interfaces configured then the highest ip
address amongst those of the loopback interfaces will be chosen as the
router ID. The advantage you get is that if the Router ID is the ip address
of a physical interface and the interface goes down then the OSPF operation
is interrupted. However, if the Router ID is that of a loopback interface
then the OSPF operation will never get interrupted as long as the router
itself does not go down and a router going down is very uncommon as compared
to an interface going down.
BGP is another routing protocol that makes use of this advantage of the
loopback interface.
I hope this clears up things a bit.
Regards
Atif
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
Stephen Skinner
Sent: Tuesday, September 12, 2000 4:35 PM
To: [EMAIL PROTECTED]
Subject: BCRAN Loopback int
Chuck,Altif,Priscilla.....save me.....
it says in my book BCRAN
"a loopback interface is a virtual interface that never goes down ,therefore
it is an ideal line to use as the reference when using the ip unnumbered
command"
i don`t understand ... a loopback interface dosen`t go
anywhere????...how,why would i reference this ....Can i have a real world
example as i don`t seem to understand WHY i would do this....
sorry i`m being a bit thick
thanks to ALL in advance
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