As per david's msg, it would seem that I may be entirely mistaken! (like thats a first
:)
headed back to study :)
pete
*********** REPLY SEPARATOR ***********
On 11/29/2000 at 8:58 AM Peter Van Oene wrote:
>One or two comments inset.
>
>Chuck's Text
>>>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.
>>
>>Well, I proved my point. Under this scenario, when I unplug the DR ethernet
>>port, the BDR becomes the DR.
>>
>>1) I am correct that in the case of the ethernet DR becoming disabled, the
>>BDR still becomes the DR.
>>
>>
>>Conclusion:
>>
>>With regards to OSPF, at least, the idea that the loopback interface
>>provides any kind of reliability is in and of itself not true. Problems
>>arise with the advertising of the loopback throughout the OSPF domain,
>>particularly when the area 0 connection is lost, and the alternate routes do
>>not propogate.
>>
>>This of course is not an issue with IGRP or EIGRP or even RIP, which do not
>>have the same restriction with regards to routing behaviours. So while in
>>OSPF the existence of a loopback interface might prove to be of no use, and
>>probably more often than one might care to imagine, it still will prove
>>quite useful within other routing protocols.
>
>A couple quick notes. The resiliency that using a loopback interface on an ospf
>router has little to do with individual segments. Naturally, if you lose an
>interface into a multi access segment you will lose your adjacencies on that segment.
>
>
>However, let consider a router with 4 interfaces. Without using a loopback
>interface, if the interface with the highest IP address dies, the routers RID
>changes. What this means is that not only does the router lose its adjacencies on
>the defective interface, it also must changes its RID to the next highest address.
>This will force it to lose and rebuild all other adjacencies and as far as I know,
>for every router in the area to recalculate their SPF tree's. Using a loopback
>address, in the same situation, this failure would be contained to the one segment.
>
>Pete
>
>
>
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