It's very simple. A loopback interface provides a connection point on a router that is not tied to a physical interface. It is very useful in many situations, for basically the same reason. Take OSPF for example. Without a loopback it will use the address of one of its physical interfaces for the routerID (unless you force it). If that interface was to go down, then the OSPF process would burp, and you'd have "problems." Using a loopback interface will ensure the same routerID no matter what the physical interfaces were doing. Take management traffic for example. Typical management applications use SNMP to poll the router for interface statistics, etc. If you polled on the primary WAN interface, for example a T1 line, and that T1 went down, then you would not be able to retrieve any statistics at all, even if you had a backup ISDN line on the router.
Fred Reimer - CCNA Eclipsys Corporation, 200 Ashford Center North, Atlanta, GA 30338 Phone: 404-847-5177 Cell: 770-490-3071 Pager: 888-260-2050 NOTICE; This email contains confidential or proprietary information which may be legally privileged. It is intended only for the named recipient(s). If an addressing or transmission error has misdirected the email, please notify the author by replying to this message. If you are not the named recipient, you are not authorized to use, disclose, distribute, copy, print or rely on this email, and should immediately delete it from your computer. -----Original Message----- From: Robert Edmonds [mailto:[EMAIL PROTECTED] Sent: Tuesday, August 05, 2003 12:47 PM To: [EMAIL PROTECTED] Subject: Re: Loopback Interface [7:73305] You gentlemen have pointed out some good uses for loopback interfaces. However, my dilema still remains that I have yet to have somebody solidly explain loopback interfaces in a way that my simple mind can understand. I have also been unsuccessful in finding any website that accomplish this. Any takers? Robert ""p b"" wrote in message news:[EMAIL PROTECTED] > terminate iBGP sessions on **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=73550&t=73305 -------------------------------------------------- **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
