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[AUDIO LOGO]

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Congratulations on
completing another skill.

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Now, it's time for a review
in the form of a quiz.

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So let's go ahead and jump
in with our first question.

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Which of the following
BGP attributes

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are generally used to effect
outbound path selection?

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So all of these can be used
to effect BGP traffic flow,

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but the key here is,
of course, that we're

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talking about outbound updates.

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And during our
discussion, we did

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mention which of these are
generally used for outbound.

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So let's go down our list.

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The first is weight.

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And weight has a very
important attribute

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towards this discussion.

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Weight is, of course,
only local to the device.

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And since it's
local to the device,

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it actually can't
affect anything other

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than the outbound
decision from that device.

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So 1, weight would definitely
be a correct answer.

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Number 2 is AS path prepending.

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Now, we haven't spoken
about this one in depth yet.

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However, this is generally
used for inbound.

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Technically, yes, it could
be used for outbound.

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But we did in the question
say, generally used to effect.

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Therefore, AS path prepending,
although it could technically

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be used for outbound
decisions, it usually is not.

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Therefore, I would
consider answer 2

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be an incorrect answer.

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Number 3 is MED.

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Once again, this is an
attribute we haven't spoken

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about in detail,
but this one also

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is used for inbound decisions.

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The idea behind MED is it will
influence the return path.

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The return path would,
of course, be inbound.

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Therefore, we're going to
consider 3 incorrect as well.

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Number 4 is local preference.

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Well, just like weight, we
have the word local here.

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However, it is local in
this case not to the router,

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but local to the AS, meaning
it's only sent in iBGP updates.

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Since it's only affecting
the local AS, once again

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without the assistance of
something else like BGP

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communities, this would, again,
only be for outbound decisions,

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making for another
correct answer.

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So in this case, our
answers are 1 and 4.

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Next question.

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Which of the following
AS paths would

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be considered equal
to 100 200 37 4

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for the purposes of
shortest AS path?

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So when we were discussing the
AS path length in our overview,

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we mentioned that it's
the number of ASes, not

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the actual values.

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So realistically,
what we have here

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is 1, 2, 3, and 4 AS numbers.

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So all we have to do is look
down our list and say 1 2

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3, that's not 4.

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So that's definitely going
to be an incorrect answer.

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1, 2, 3, 4, that one's 4.

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So that is a correct answer.

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Remember, we're
looking for equal here.

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So our next answer,
1, 2, 3, 4, 5.

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Clearly that's not correct.

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So 3 is incorrect.

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And of course, answer
4 here 1, 2, 3, 4.

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And again, clearly correct.

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So in this example, 2 and
4 are both four AS numbers,

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which would be equal
to the given path.

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Next question.

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What will be the default
weight of a prefix

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if it's learned
from an iBGP peer?

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So two big things we
need to consider here.

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First, of course,
we're looking at weight

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and we're looking at learned.

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In this particular
case, it really

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doesn't matter if it's iBGP.

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It's just the fact that
it's a learned route.

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So let's go down our list.

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Number 1-- 16384, this is
actually not the default value

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for anything in BGP.

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Number 2-- 32768, well,
this one can actually

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be the default weight,
but only if the prefix

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is being injected locally.

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Therefore, once again, 2
would be an incorrect answer.

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Just to skip ahead for
a moment, number 4--

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100, this one's actually the
default for local preference,

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but not for weight.

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So again, 4 would be
an incorrect answer.

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The correct answer is
for a learned prefixes,

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the default weight will be 0.

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Remember, weight highest wins.

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Therefore, 0 is actually
the worst value.

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Final question.

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Which of the following paths
would be chosen as best?

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So here we're given
a variety of paths

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with different attributes.

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Now, the first thing to keep
in mind is weight, of course,

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is going to be considered first.

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So what we have to do is
we have to look to see

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if the weights are equal.

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We have a weight of
90, a weight of 100,

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and then we have
two weights of 110.

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So what's going to
happen at this point

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is BGP is going to choose
the highest weight.

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That means that path 1
is going to be eliminated

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and path 2 is going
to be eliminated.

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Then it will look
at paths 3 and 4,

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and it'll look next
to local preference.

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Here we have a local
preference of 100

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and a local preference of 200.

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Highest local preference wins.

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So once again, what's
going to happen here

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is path 3 will be eliminated.

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And that means that
path 4 is going

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to be our correct answer
with a weight of 110

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and a local preference of 200.

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So that concludes this quiz.

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If you find that you are missing
any of the information needed

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to answer these
questions, please

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be sure to go back and
review the referenced videos

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on each question.

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Otherwise, congratulations
on completing

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explain outbound
BGP path selection.

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I hope this has been
informative for you,

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and I'd like to thank
you for viewing.

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