Just to put in some empirical data, I set up two routers on an Ethernet
link, in the classic OSPF broadcast scenario. Hello time is 10 seconds. Dead
time 40 seconds ( 4xhello )
I determined which of the two routers was the DR, and which was the BDR
I then plugged into and monitored from the BDR, using repeated "show ip ospf
neighbor" commands
I then unplugged the DR from the ethernet
I then repeatedly reissued the show ip ospf neighbor commands
I watched.
The result of the show command was that the neighbor state FULL/DR remained
in effect until the dead time was reached. After that, there was no
neighbor.
I also plugged it the first router back into the ethernet and repeatedly
issued the commands. After a few seconds the first router showed up as a
FULL/BDR
Of some interest - the debug ip ospf hello and debug ip ospf events were
silent immediately after unplugging the DR. It was only after the expiration
of the dead time that debug ip ospf events indicated the election of a new
DR, to whit, the router I was monitoring.
Where this 0.5 second / half second thing comes from I cannot say. But using
Cisco's defaults in a quick and dirty lab, it is safe to say that this is
not what happens.
Chuck
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of
Matthew Herman
Sent: Friday, November 10, 2000 9:56 AM
To: David Armstrong; [EMAIL PROTECTED]
Subject: RE: Some OSPF Questions
I'll throw my hat in..
1. .5 seconds (50 msec) (Chapter 7, p142 exam cram acrc)
2. yes, there will be only one DR and its your single point of failure as
well 8->.
3. doh...I have set up multiple as's on one router when I had multiple
customer and redistributed into my AS. It worked ok but I am not saying
that was a good way of configuring the router.
2/3 = 66 percent.... Still not enough to pass the ccie...
matt
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of David
Armstrong
Sent: Friday, November 10, 2000 8:46 AM
To: [EMAIL PROTECTED]
Subject: Some OSPF Questions
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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