[AUDIO LOGO]
Let's be honest here.
One of the most important things in a service provider corps
is redundancy.
We have redundancy on everything.
However, if we're just doing a link-local session for LDP,
that doesn't have any redundancy.
But LDP does give us another option.
It's called Session Protection, and it's relatively easy
to set up and configure.
So let's go ahead and talk about how to configure it,
the different parameters that we can modify and change,
and just take a look at some of those details
with Session Protection.
So, of course, the main point of Session Protection
is using this to back up a normal LDP neighborship.
Now we do have a couple options when
it comes to configuring this.
First is, we can either configure
this for all of our neighbors, or we
can configure an access control list or an ACL
and choose which neighbors to actually protect
with Session Protection.
The other thing to note is if we don't do anything,
we won't have Session Protection because this
is, in fact, disabled by default.
So we would have to actually enable it.
The way it actually functions is it
sends targeted unicast hellos to the neighbors
that are on that ACL that we also
have primary adjacencies to.
So fundamentally, the way this works is you
already have to have a primary LDP neighborship with a peer,
and then session protection assuming
that peer is on the ACL, will then
start this unicast targeted hello
neighborship to that same peer.
But we do have that initial requirement
that the other router has to already be, we'll say,
a normal LDP neighbor.
And, of course, the whole purpose of this
is that backup-targeted hellos are
going to maintain that LDP adjacency when
the primary link goes down.
This is, after all, why we are calling it session protection.
It's protecting that neighborship.
Something else we can configure is the duration
that backup session is going to stay up,
assuming that the primary session doesn't come back.
So again, the scenario we're talking about here
is your primary neighborship goes down.
We switch over to our session protection
targeted neighborship.
And then the question is if that primary neighborship never
comes back up or doesn't come back up for what duration,
should we then just say, OK, well, I
guess we should just forget that neighbor then,
and we tear down the backup as well.
Now as we can see here, we can certainly
configure this to infinite or never, basically
keep that backup session up and running forever.
May or may not be the best idea.
Normally, of course, backup solutions
are meant to be temporary until we fix the primary problem.
However, maybe, it's going to take us
longer to fix that primary session,
and we need to keep the backup session longer.
The default, if we don't change anything,
is to keep the backup up and running for 24 hours.
So if we don't change anything, that's
what it's going to do by default. Now
the command to enable this is, of course, a little bit
different on each platform.
On IOS XR, the command is simply session protection
under the LDP configuration.
And on IOS XE, the command is mpls ldp session protection
under global configuration.
So although the commands are slightly different,
it does function the same way on both platforms.
In this video, we saw how to back up our primary LDP
neighborship with a backup session using targeted hellos
called Session Protection.
We also took a look at the commands
that we can use to enable this on both IOS XR and IOS XE,
and we talked a bit about how long
that backup circuit will be maintained
if the primary circuit doesn't come back online.
Now the circuit itself, of course,
is not the only thing that can fail that might
cause LDP to go down.
We could have something like a route
processor fail in our devices.
And to handle situations like that,
we have technologies like non-stop forwarding,
non-stop routing, stateful switchover, and so on.
And we're going to talk about some
of those things coming up next.
Until then, I hope this has been informative for you,
and I'd like to thank you for viewing.