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Congratulations on completing another skill.
Now, it's time for a review in the form of a quiz.
So let's go ahead and jump in with our first question.
Which of the following BGP attributes
are generally used to effect outbound path selection?
So all of these can be used to effect BGP traffic flow,
but the key here is, of course, that we're
talking about outbound updates.
And during our discussion, we did
mention which of these are generally used for outbound.
So let's go down our list.
The first is weight.
And weight has a very important attribute
towards this discussion.
Weight is, of course, only local to the device.
And since it's local to the device,
it actually can't affect anything other
than the outbound decision from that device.
So 1, weight would definitely be a correct answer.
Number 2 is AS path prepending.
Now, we haven't spoken about this one in depth yet.
However, this is generally used for inbound.
Technically, yes, it could be used for outbound.
But we did in the question say, generally used to effect.
Therefore, AS path prepending, although it could technically
be used for outbound decisions, it usually is not.
Therefore, I would consider answer 2
be an incorrect answer.
Number 3 is MED.
Once again, this is an attribute we haven't spoken
about in detail, but this one also
is used for inbound decisions.
The idea behind MED is it will influence the return path.
The return path would, of course, be inbound.
Therefore, we're going to consider 3 incorrect as well.
Number 4 is local preference.
Well, just like weight, we have the word local here.
However, it is local in this case not to the router,
but local to the AS, meaning it's only sent in iBGP updates.
Since it's only affecting the local AS, once again
without the assistance of something else like BGP
communities, this would, again, only be for outbound decisions,
making for another correct answer.
So in this case, our answers are 1 and 4.
Next question.
Which of the following AS paths would
be considered equal to 100 200 37 4
for the purposes of shortest AS path?
So when we were discussing the AS path length in our overview,
we mentioned that it's the number of ASes, not
the actual values.
So realistically, what we have here
is 1, 2, 3, and 4 AS numbers.
So all we have to do is look down our list and say 1 2
3, that's not 4.
So that's definitely going to be an incorrect answer.
1, 2, 3, 4, that one's 4.
So that is a correct answer.
Remember, we're looking for equal here.
So our next answer, 1, 2, 3, 4, 5.
Clearly that's not correct.
So 3 is incorrect.
And of course, answer 4 here 1, 2, 3, 4.
And again, clearly correct.
So in this example, 2 and 4 are both four AS numbers,
which would be equal to the given path.
Next question.
What will be the default weight of a prefix
if it's learned from an iBGP peer?
So two big things we need to consider here.
First, of course, we're looking at weight
and we're looking at learned.
In this particular case, it really
doesn't matter if it's iBGP.
It's just the fact that it's a learned route.
So let's go down our list.
Number 1-- 16384, this is actually not the default value
for anything in BGP.
Number 2-- 32768, well, this one can actually
be the default weight, but only if the prefix
is being injected locally.
Therefore, once again, 2 would be an incorrect answer.
Just to skip ahead for a moment, number 4--
100, this one's actually the default for local preference,
but not for weight.
So again, 4 would be an incorrect answer.
The correct answer is for a learned prefixes,
the default weight will be 0.
Remember, weight highest wins.
Therefore, 0 is actually the worst value.
Final question.
Which of the following paths would be chosen as best?
So here we're given a variety of paths
with different attributes.
Now, the first thing to keep in mind is weight, of course,
is going to be considered first.
So what we have to do is we have to look to see
if the weights are equal.
We have a weight of 90, a weight of 100,
and then we have two weights of 110.
So what's going to happen at this point
is BGP is going to choose the highest weight.
That means that path 1 is going to be eliminated
and path 2 is going to be eliminated.
Then it will look at paths 3 and 4,
and it'll look next to local preference.
Here we have a local preference of 100
and a local preference of 200.
Highest local preference wins.
So once again, what's going to happen here
is path 3 will be eliminated.
And that means that path 4 is going
to be our correct answer with a weight of 110
and a local preference of 200.
So that concludes this quiz.
If you find that you are missing any of the information needed
to answer these questions, please
be sure to go back and review the referenced videos
on each question.
Otherwise, congratulations on completing
explain outbound BGP path selection.
I hope this has been informative for you,
and I'd like to thank you for viewing.