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Home > Archive > alt.certification.cisco > February 2004 > question of the day
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| Author |
question of the day
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| binary 2004-02-19, 10:24 am |
| Which two problems can occur when a single OSPF area has too many routers?
(Choose two)
A. Excessive LSA traffic.
B. Frequent routing table recalculation.
C. Frequent adjacencies table recalculation.
D. Unacceptable number of reachability errors.
anyoone ?
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| Bob by The Bay 2004-02-19, 4:25 pm |
| While all 4 answers have merit, the problems I experienced in this situation
that most impacted the network were answers C & D.
That is, as the network grows the number of adjacencies tends to grow
exponentially, thus a recalculation tends to put much greater demand on a
router CPU. On lower end routers, having the CPU pegged during the
recalculation process can cause throughput and reachability issues, which in
turn can feed the network with increasing recalculations and further
instability and finally route flapping.
Of course there are also excessive LSA traffic and frequent router table
recalculation as a result.
FWIW,
Robert
"binary" <binary_0011@hotmail.com> wrote in message
news:4034cf3a$1@news.starhub.net.sg...
> Which two problems can occur when a single OSPF area has too many routers?
> (Choose two)
>
> A. Excessive LSA traffic.
>
> B. Frequent routing table recalculation.
>
> C. Frequent adjacencies table recalculation.
>
> D. Unacceptable number of reachability errors.
>
> anyoone ?
>
>
| |
| binary 2004-02-20, 9:25 am |
| why wasn't A the answer?
"Bob by The Bay" <nospam@forthisposter.org> wrote in message
news:5O8Zb.14700$Xp.77048@attbi_s54...
> While all 4 answers have merit, the problems I experienced in this
situation
> that most impacted the network were answers C & D.
>
> That is, as the network grows the number of adjacencies tends to grow
> exponentially, thus a recalculation tends to put much greater demand on a
> router CPU. On lower end routers, having the CPU pegged during the
> recalculation process can cause throughput and reachability issues, which
in
> turn can feed the network with increasing recalculations and further
> instability and finally route flapping.
>
> Of course there are also excessive LSA traffic and frequent router table
> recalculation as a result.
>
> FWIW,
> Robert
>
> "binary" <binary_0011@hotmail.com> wrote in message
> news:4034cf3a$1@news.starhub.net.sg...
routers?[color=blue]
>
>
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| Bob by The Bay 2004-02-20, 12:26 pm |
| It's true that subdividing a network into well sized areas and stub areas
keeps the LSAs down to a reasonable level. And of course it may be argued
that an increase in LSAs precedes and increase in recalculations of the
adjacencies. A & C would be my runner-up. From a test and study
perspective A & C may be what is expected - I honestly don't know and would
be curious to find out. If A & C are the answer, then D would be viewed as
the result rather than the cause I suppose.
I'm going solely by what I experienced. In my case, bandwidth wasn't being
overtaken by LSAs and wasn't directly causing my network problems. The
weaker routers were being maxed out by the SPF processing demands, directly
causing router throughput problems. Because intermittent reachability and
adjacency recalcs feed each other in an escalating cycle, I perceived these
to be the 2 more serious issues when experiencing the problems.
Don't you just love shades of gray?
Perhaps someone else can be more authoritative on this question.
Robert
"binary" <binary_0011@hotmail.com> wrote in message
news:40360ca5$1@news.starhub.net.sg...
> why wasn't A the answer?
>
>
> "Bob by The Bay" <nospam@forthisposter.org> wrote in message
> news:5O8Zb.14700$Xp.77048@attbi_s54...
> situation
a[color=blue]
which[color=blue]
> in
> routers?
>
>
| |
|
| I'll choose "A".
"binary" <binary_0011@hotmail.com> wrote in message
news:4034cf3a$1@news.starhub.net.sg...
> Which two problems can occur when a single OSPF area has too many routers?
> (Choose two)
>
> A. Excessive LSA traffic.
>
> B. Frequent routing table recalculation.
>
> C. Frequent adjacencies table recalculation.
>
> D. Unacceptable number of reachability errors.
>
> anyoone ?
>
>
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