At 11:25 PM 11/27/00, Chuck Larrieu wrote:
>Yes and no. recall that a DR is elected on a shared broadcast medium,
>typically ethernet. ( dumb question - how does this play out in a token ring
>environment? My supposition is that it would work out the same, even though
>TR is not a broadcast medium )
Token Ring is a broadcast medium. Every station on a ring sees every frame.
I'll leave the real answer to someone else. Thanks for all your great study
challenges and answers, Chuck!
Priscilla
>So if you were to change your scenario to the ethernet port going down, then
>yes.
>
>Hhhhmmmm.......
>
>Suppose you had:
>
>------------------------------------- ethernet
>| | |
>DR BDR DR/other
>| |
>(---frame relay cloud ---)
>
>DR ethernet hardware fails.
>
>Now then, given that the DR hello is roughly 10 seconds by default, will the
>BDR be promoted to DR even though there is an alternate route to the
>existing DR. Recall that the SPF would most definitely be the ethernet port.
>Would there be a footrace among the various router interfaces? Would the
>alternate route to the DR be propagated to everyone prior to the BDR
>promotion? Without doing a Q&D lab, I would venture a guess that the BDR
>would be promoted because even though there is an alternative route to the
>DR loopback, hellos go only to adjacent routers, and the DR is no longer
>adjacent.
>
>Any comments?
>
>Can't answer number 2. As my real world OSPF experience is limited.
>
>Chuck
>
>
>-----Original Message-----
>From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of
>whitaker
>Sent: Monday, November 27, 2000 9:43 PM
>To: [EMAIL PROTECTED]
>Subject: RE: question about loopback interfaces
>
>Thanks for the response! I have two more questions:
>
>If in an OSPF and BGP environment, I think can see the stability with
>loopbacks... Correct me if I'm wrong in this theoritical scenario:
>Two routers in an OSPF share the highest priority. To break the tie and
>determine the DR, OSPF looks at router id, which is the highest interface
>address (let's say serial interface) and determines a particular router has
>the highest id. It becomes DR. Without a loopback address, if the serial
>interface goes down, then the BDR comes online and a new BDR election takes
>place. This requires processing power and could slow down the network.
>With a loopback interface configured with the highest IP address, then if a
>router is the DR and looses its serial interface, it would remain the DR.
>Is this correct?
>
>My second question involves the configuration of the loopback from
>real-world experience. What do most of you use - an address from the same
>subnet one of the interfaces is on or a seperate address?
>
>
>
>
>-----Original Message-----
>From: Tony van Ree [mailto:[EMAIL PROTECTED]]
>Sent: Monday, November 27, 2000 9:28 PM
>To: whitaker; [EMAIL PROTECTED]
>Subject: Re: question about loopback interfaces
>
>
>The notes I have here suggest that using a loopback interface provides a
>more stable interface than a physical interface. As the loopback interface
>is up as long as the RAM is working the chances of losing this interface are
>greatly reduced.
>
>Both OSPF and BGP use the highest active IP address as the router ID. If a
>loopback address is configured they will use the loopback address.
>Therefore the loopback address provides more stability.
>
>It can also make network management and troubleshooting tasks easier.
>
>Teunis.
>On Monday, November 27, 2000 at 08:58:00 PM, whitaker wrote:
>
> > Could someone explain the importance of using loopback interfaces? I keep
> > reading that it is important when using routing protocols to use loopback
> > interfaces. A consultant that is writing documentation for me suggested I
> > obtain an entire class C network just for loopback addresses. Cisco says
> > when configuring BGP that, "We recommend you use a loopback interface to
> > guarantee reachability in networks with multiple paths." (from
> > http://www.cisco.com/warp/public/459/23.html#3).
> >
> > Maybe I'm missing something totally obvious here, but exactly what benefit
> > do I gain from using loopback addresses? I know it is supposed to provide
> > reliability for routing protocols, but how?
________________________
Priscilla Oppenheimer
http://www.priscilla.com
_________________________________
FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
