"David Armstrong" <[EMAIL PROTECTED]> wrote,
>This has been an awesome thread to me. Thanks everyone for the input.
>Evidently I'm not alone in being confused over BDR to DR promotion. The
>books and literature I've found have clearly stated that the event to
>promote BDR's to DR's is a missed LSA; however, the tests here show
>otherwise. Winston, I'm with you: I hope they never ask this on the test.
>I'll have to decide between what I believe to be right and what the book
>states as right.
I'd be surprised if it were asked. In general, however, take the RFC
over any review materials. In this case, though, I will quote a bit
from John Moy's _OSPF: Anatomy of an Internet Routing Protocol_ book.
John is the principal author/editor of the OSPF specification.
There really is more than one failure mode to consider:
(Moy p 106) "If the DR fails, so does database synchronization over
the broadcast subnet. OSPF deals with this problem by electing a BDR
for the broadcast subnet. All routers synchronize with both the DR
and BDR, and the BDR acts as a hot standby in case the DR fails."
(Moy p 107) " ...if the BDR does not see the Link State Update from
the DR within the LSA retransmission interval (typically 5 seconds),
it will step in and flood the LSA back onto the Ethernet in order to
keep the database synchronization going. "
So, if active updating is going on, the BDR will act to keep that
process working before a DR is elected. The absence of a DR,
especially when the subnet is otherwise idle, will be detected by
missing hellos, by the dead timer.
>I still think there's a piece missing. 40 seconds to take over the functions
>of DR seems like it could create routing delays or time outs on a large
>network. I'm going to continue to look for a definitive answer.
You are pointing to a very real problem in available protocols. See
http://www.nanog.org/mtg-0010/ppt/cengiz.pdf for some research
approaches to subsecond convergence times.
>
>Thanks Again,
>
>David
>
>""David Armstrong"" <[EMAIL PROTECTED]> wrote in message
>8uh8vj$c47$[EMAIL PROTECTED]">news:8uh8vj$c47$[EMAIL PROTECTED]...
>> Last night at our BSCN study group meeting in Dallas we had some questions
>> about OSPF that we weren't able to resolve. If someone or ones could
>answer
>> these it would clarify some areas we're a little fuzzy on. Also, if you're
>> iin the Dallas Ft. Worth area and would like to attend, we'd love to have
>> you join us..
>>
>> Thanks for any help,
>>
>> David Armstrong
>>
>>
>> 1) What is the default time period that the BDR waits when listening to
>> LSA's from the DR before it decides that the DR is down and promotes
>itself
>> to DR. All the literature we could find simply said that the BDR waits for
>> the specified time period but never said what that period is.
>>
>> 2) In a Point-to-Point network in which the router in Area 0 is connected
>to
>> FR, ISDN, X.25 or ATM branch offices (networks), how does convergence and
>> updates take place? From what we've found a DR and BDR is not elected in a
>> strictly Point-to-Point network.
>>
>> I think an example would explain this question better: We have one 3620
>> router in our Ft. Worth office connected to an office in Houston (via FR),
>> and office in Kansas City (via FR), an office in the DFW area (via ISDN)
>and
>> the owner's home (via ISDN). The 3620 is behind a firewall (Pix 520) and
>the
>> firewall is connected to a 1720 going to the Internet. I'd like to
>implement
>> OSPF on our network simply for the experience. However, I don't have 2
>> routers internally on our Ethernet LAN that can be configured for Area 0
>and
>> elected to DR and BDR. All other routers connected to that router are via
>> NBMA Point-to-Point connections. Since I only have one router on the
>> Broadcast Multiaccess network (the 3620) and routers connected via PtoP
>> don't participate in DR and BDR elections, how would updates occur? Can
>> their only be one DR (in this case the 3620)?
>>
>> 3) The books and tutorials all state that "router ospf 6" defines ospf on
> > the router with a process ID of 6. They then all say that you shouldn't
>> define more than one process. Does that mean that you can have a router
>with
>> the following:
>>
>> router ospf 6
>> network 10.100.0.0 0.0.255.255
>>
>> router ospf 7
>> network 10.200.0.0 0.0.255.255
>>
>> If this is an allowed configuration, what kind of instances would it be
>used
>> for? Also, exactly what is the process ID used for?
>>
>>
>>
>>
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