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[AUDIO LOGO]

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Let's be honest here.

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One of the most important things
in a service provider corps

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is redundancy.

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We have redundancy
on everything.

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However, if we're just doing
a link-local session for LDP,

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that doesn't have
any redundancy.

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But LDP does give
us another option.

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It's called Session Protection,
and it's relatively easy

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to set up and configure.

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So let's go ahead and talk
about how to configure it,

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the different parameters that
we can modify and change,

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and just take a look at
some of those details

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with Session Protection.

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So, of course, the main
point of Session Protection

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is using this to back up
a normal LDP neighborship.

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Now we do have a
couple options when

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it comes to configuring this.

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First is, we can
either configure

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this for all of our
neighbors, or we

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can configure an access
control list or an ACL

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and choose which neighbors
to actually protect

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with Session Protection.

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The other thing to note is
if we don't do anything,

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we won't have Session
Protection because this

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is, in fact,
disabled by default.

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So we would have to
actually enable it.

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The way it actually
functions is it

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sends targeted unicast
hellos to the neighbors

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that are on that
ACL that we also

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have primary adjacencies to.

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So fundamentally, the
way this works is you

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already have to have a primary
LDP neighborship with a peer,

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and then session
protection assuming

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that peer is on
the ACL, will then

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start this unicast
targeted hello

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neighborship to that same peer.

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But we do have that
initial requirement

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that the other router has
to already be, we'll say,

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a normal LDP neighbor.

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And, of course, the
whole purpose of this

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is that backup-targeted
hellos are

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going to maintain that
LDP adjacency when

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the primary link goes down.

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This is, after all, why we are
calling it session protection.

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It's protecting
that neighborship.

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Something else we can
configure is the duration

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that backup session
is going to stay up,

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assuming that the primary
session doesn't come back.

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So again, the scenario
we're talking about here

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is your primary
neighborship goes down.

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We switch over to our
session protection

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targeted neighborship.

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And then the question is if
that primary neighborship never

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comes back up or doesn't come
back up for what duration,

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should we then just
say, OK, well, I

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guess we should just
forget that neighbor then,

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and we tear down
the backup as well.

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Now as we can see
here, we can certainly

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configure this to infinite
or never, basically

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keep that backup session
up and running forever.

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May or may not be the best idea.

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Normally, of course,
backup solutions

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are meant to be temporary until
we fix the primary problem.

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However, maybe, it's
going to take us

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longer to fix that
primary session,

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and we need to keep the
backup session longer.

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The default, if we
don't change anything,

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is to keep the backup up
and running for 24 hours.

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So if we don't change
anything, that's

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what it's going to
do by default. Now

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the command to enable this
is, of course, a little bit

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different on each platform.

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On IOS XR, the command is
simply session protection

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under the LDP configuration.

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And on IOS XE, the command is
mpls ldp session protection

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under global configuration.

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So although the commands
are slightly different,

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it does function the same
way on both platforms.

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In this video, we saw how
to back up our primary LDP

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neighborship with a backup
session using targeted hellos

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called Session Protection.

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We also took a look
at the commands

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that we can use to enable this
on both IOS XR and IOS XE,

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and we talked a
bit about how long

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that backup circuit
will be maintained

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if the primary circuit
doesn't come back online.

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Now the circuit
itself, of course,

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is not the only thing
that can fail that might

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cause LDP to go down.

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We could have
something like a route

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processor fail in our devices.

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And to handle
situations like that,

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we have technologies
like non-stop forwarding,

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non-stop routing, stateful
switchover, and so on.

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And we're going
to talk about some

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of those things coming up next.

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Until then, 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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