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[AUDIO LOGO]

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Now that we've looked at route
maps on IOS XE, let's jump in

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and look at the
similar feature that we

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have on IOS XR, which is
routing policy language, or RPO.

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Now it's similar in that we
use it to handle those advanced

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route filtering and
manipulation issues that we need

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to accomplish on our devices.

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It's a little bit different in
that, well, it's more advanced.

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It addresses some of the issues
that we have with route maps.

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Now this is very much a
scripted-type language.

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We're going to be using if,
then, else, endif, things

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like this, and use
that to both filter

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and manipulate our routes.

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So, in this video,
what we're going to do

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is jump in and take a look
at the formatting of RPO

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and some of the
different options we have

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and how it gets
processed on the devices.

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So let's go ahead and
jump in and take a look

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at those details.

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So, again, RPO is the upgraded
or more advanced version

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of route maps.

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And this is, of
course, what we have

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that's available on IOS XR.

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What shortcomings of route maps
was routing policy language

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designed to fix?

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Well, first, it has
better modularity.

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We can re-use pieces
in different scripts.

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So that also goes with
the better reusability.

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It also has
parameterization, which

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we'll take a look at
this in the next video

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when we get into more
advanced features.

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However, this is sort of like
using variables in a script.

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We can use this to pass values
between RPO scripts and things

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like this.

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We can also do nesting, both
for policies and conditions.

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We have very powerful
match options--

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again, we'll be looking
at those as well--

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and reusable value sets.

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Now the reusable value
sets, to a certain extent,

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are a little bit
like the access lists

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and the prefix lists that
we use with route maps.

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And we could reuse those in
different route maps too,

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but these are value sets that
are very easy to work with.

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Another difference between
route maps and RPO--

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RPO is not made up of
statements like route maps are,

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but instead, it's a policy.

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Again, this is much
more like a script.

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This is defined between
the opening words, where

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we start defining
our route policy,

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and the end policy command,
which is where the policy ends.

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So as we're writing
it, everything

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will start with
route-policy, and then

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once we've written
the whole policy,

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end-policy is how we exit
and save that policy.

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Now, of course, where they're
similar to route maps is

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they can filter and
manipulate routes.

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That's really the
whole purpose of this.

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To do this, we do
have some keywords.

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First, we have pass and drop.

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These are the commands that are
going to be used for filtering.

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Anything, of course, that is
set to pass will be permitted.

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Anything set to drop
will be dropped.

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And then, for manipulation
or modification of the route,

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we'll use set or delete.

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Now don't confuse
delete with drop.

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Drop, of course, means we're
dropping the route itself.

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Delete means we would be,
say, deleting an attribute.

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Maybe it's a BGP route that
has a certain community

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string on it.

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And we want to remove
that community string.

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Or maybe we want to
remove a route tag

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from a particular route.

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This is where the
delete comes in.

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So, again, delete is not
about whether we're permitting

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or denying the route.

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It's about removing attributes.

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So next up here, we have
quite a few rules about RPO

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that we want to be aware of.

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So let's make sure we
go through each of these

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and understand what they are.

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First is the default action, if
we don't specify, is to drop.

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This means, of course,
that an empty policy where

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we haven't specified
anything will implicitly

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deny all routes.

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So that's our first rule.

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Second, if you do an explicit
pass without any conditions,

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that will then
forward all routes.

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Now it won't change
anything about those routes.

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It will just forward
them through.

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So, again, there would be
no modifications to those.

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But they will simply be sent.

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Now rule number three here--

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an explicit drop
will do the same

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as an implicit drop, which
means it's literally just doing

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the same thing here.

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One advantage here is you
can get some logging on this.

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For our fourth
rule, our statement

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is that a set command will, of
course, modify the attributes--

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whatever it's set to change--

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and it will forward
all the routes.

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There's an implicit pass
when you use a set command.

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So you don't have to
specifically put in pass.

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Truth be told, I usually
still put pass in there,

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even when I do a
set, because I find

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it's a little bit easier
to read through later.

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That's just personal preference.

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You can certainly
put your own pass,

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but you don't have to as long
as there's a set command.

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And the last thing here is
if there's an explicit drop--

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so again, this is pretty much
what we did in statement three

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up here--

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but it will stop the
processing of the policy,

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denies the route, even if
there are other statements.

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Essentially, what
this last statement

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is saying is if the
action is to drop,

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it's going to ignore
any set commands.

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You don't want to modify
something if you're just

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going to discard it.

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The analogy I always use here
is if you're going to scrap

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your car-- it's no good,
you're going to send it

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to the junkyard--

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you don't usually
wash it, sand it down,

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and paint it so it looks
nice before you send it

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to the junkyard.

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Why would we modify something--
make it better, different,

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whatever-- if we're just
going to discard it anyway?

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So again, if there is a
drop statement, that's it.

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It stops all processing.

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So even if you put set commands
on that same statement,

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they would be ignored.

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So let's talk about some of
those conditional statements

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that we can use.

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So in the spirit of this
being a lot like a script,

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we have things like if, elseif--

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so, of course, that means if
the if statement is not true,

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it will then do
this other thing.

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You can also just do an
else, and we have endif

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to close that statement out.

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Conditions can be used in
these operators as well.

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We have equals, less than
or equal to, greater than

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or equal to, is, and in.

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A little bit of
clarification here--

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first off, we have equals
which, you might remember,

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we don't really
have on route maps

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and prefix lists and
things like that.

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Remember, we had to
use a combination

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of less than or equal to or
greater than or equal to.

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Here, we actually
have an equals.

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So you might look at that
and say, well, that's cool.

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But if we haven't equals,
then what is the is?

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How are those different?

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Well, equals is
going to be numeric.

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This will be some sort
of a numeric value.

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"Is" can be any kind of value.

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So, again, usually,
we would use equal

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because most of the things
we're going to be looking at

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will be numeric values.

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But if there's something else we
want to look at, we can say is.

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In if we're going to
use one of our sets.

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We'll be talking about
these in a little bit.

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But that's the basic idea behind
these different conditions.

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We can also use
Boolean operators.

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So we have available
and, or, and not.

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The way these work is
they can be combined.

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Not is processed first,
then and, and then or.

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So that's the order
of operations.

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However, that can be
modified with parentheses.

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So to a certain extent,
it's a little bit

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like an algebraic equation.

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We can modify the
order of operations

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based on the use of parentheses.

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Again, the best way to see this
is maybe to look at an example.

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So let's do that.

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So, our first example here,
we have no parentheses.

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We're not counting the
ones around the community

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back here, where we're saying
that we can match anything

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in that community string.

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So let's just look at
the statement itself.

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So the first thing is that
the med has to equal 100,

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and we sort of have two
operators together here--

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and not the local
preference equals 200.

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So really, there's
two conditions here

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where a route would
pass through this.

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First, if the med was 100
and the local preference

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was, say, 250, that would
match the first part of this

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that's in front of the or.

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So that means the route
would meet this criteria.

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Or we could have a route
where the community is 1000:1.

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So, essentially, what
we're saying here

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is the split on this statement
is right here at the or.

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We either have to meet the
first part or the second part.

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The first part is a
little more complicated

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because, again, it's compound.

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It's an and not.

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So what would not meet
this is, of course,

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if it was 100 and 200.

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That would not match
because it's not

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local preference equals 200.

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Now looking at the
second statement,

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we now introduce a
set of parentheses,

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and this is where things
get interesting because now

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what we have is an and.

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So now we have to meet
both of these criteria

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because the and is
outside the parentheses.

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Now the first criteria in
this one is fairly simple.

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The med has to equal 100.

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So a route comes in
with a med of 100.

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That's fine.

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And what?

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And it's either not a
local preference of 200

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or the community of 1000:1.

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So what would match this?

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Well, if the local
preference was 250, again,

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that would be OK.

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Or maybe something
comes in and it's

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100 with a local
preference of 200,

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but the community is 1000:1.

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So it's not matching
the local preference,

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but it is matching
on the community.

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So that would still be OK.

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What would not match
in this case is

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if it comes in
with a med of 100,

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the local preference is 200,
and the community string

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is 1010:10--

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something different.

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This is no good because it
doesn't meet the or criteria.

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The community
string is not right,

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and the local preference
is supposed to not be 200.

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So, in this case,
it doesn't meet

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either side of the criteria.

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The last example is
really interesting

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because all we really do
is change the position

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of the parentheses.

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Now it's and not, which
means the second half of this

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has to be not true.

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Now once again, we have
the med has to equal 100.

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And you might have
noticed, I haven't really

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been messing with the
med in these examples

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because it's fairly
straightforward.

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So OK, fine-- once
again, the med

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has to equal 100 and
not the local preference

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being 200 or the
community being 1000:1.

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So what would meet
this criteria?

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Well, local preference
could be 250.

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That's not 200.

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Or the community
could be 1010:10.

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That would be good because
that's a med of 100

250
00:13:27,570 --> 00:13:30,750
and not a local
preference of 200

251
00:13:30,750 --> 00:13:35,010
and not a community of 1000:1.

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00:13:35,010 --> 00:13:40,770
What would not match
this is if my med was 100

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00:13:40,770 --> 00:13:49,710
and my local preference was 200
and my community was 1010:10.

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00:13:49,710 --> 00:13:53,040
Where this is
failing is it's not

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00:13:53,040 --> 00:14:00,060
supposed to be 200 or 1000:1.

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00:14:00,060 --> 00:14:02,910
Well, unfortunately,
this one's a 200,

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00:14:02,910 --> 00:14:08,810
so that fails the not 200
part, just like if I had 100--

258
00:14:08,810 --> 00:14:10,890
250.

259
00:14:10,890 --> 00:14:14,400
So that matches
the not 200 part,

260
00:14:14,400 --> 00:14:19,350
but if my community was 1000:1--

261
00:14:19,350 --> 00:14:22,950
once again, that still wouldn't
pass the criteria because the

262
00:14:22,950 --> 00:14:26,650
or is now on the not part of it.

263
00:14:26,650 --> 00:14:29,940
So, as you can see, just
with changing the parentheses

264
00:14:29,940 --> 00:14:32,760
around a little bit,
we have completely

265
00:14:32,760 --> 00:14:36,840
changed the meaning of this
statement three different ways

266
00:14:36,840 --> 00:14:39,510
with the exact same statements.

267
00:14:39,510 --> 00:14:41,970
The only difference
is the parentheses,

268
00:14:41,970 --> 00:14:45,450
and it completely changes
what these matches mean.

269
00:14:45,450 --> 00:14:48,450
This is why it's so important to
understand how the parentheses

270
00:14:48,450 --> 00:14:53,030
work, the and, the
not, and the or.

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00:14:53,030 --> 00:14:58,030
So, in this video, we talked a
bit about the structure of RPO.

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00:14:58,030 --> 00:15:00,850
We talked about the
different operators we have,

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00:15:00,850 --> 00:15:04,780
our Boolean variables,
if-then-else statements.

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00:15:04,780 --> 00:15:07,270
So now what we're
going to do is move

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00:15:07,270 --> 00:15:10,540
on to some of the more
advanced features of RPO

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00:15:10,540 --> 00:15:12,380
in our next video.

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00:15:12,380 --> 00:15:16,060
Until then, I hope this has
been informative for you,

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00:15:16,060 --> 00:15:19,140
and I'd like to thank
you for viewing.

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