[AUDIO LOGO]
So during our introduction, we mentioned the fact
that segment routing completely changes the way the control
plane works in regard to MPLS.
Specifically, how the labels are going
to be exchanged between the devices.
We're going to be getting rid of LDP
and, actually, RSVP as well, and instead use
our IGPs, OSPF, and IS-IS.
We'll also take a look in this video
about some other options we have available,
such as using a controller or even using BGP.
So let's go ahead and take a look
at how we change the control plane to handle
segment routing.
So one of the big advantages to the changing of the control
plane is, since we're not using other protocols,
we're just using our IGP and/or other routing protocols
that we're already using.
This control plane for segment routing is far less complex.
We're using those routing protocols
that were already in place to distribute the labels.
And since that's what we're doing,
there's no dedicated protocol.
So that means that LDP and RSVP are no longer going
to be used in the environment.
So, of course, instead, that means
we're going to be using either our IGP, which
in the case of IS-IS means we're going
to be using new TLVs, or type-length-values,
and in the case of OSPF, it's going to use something called
opaque LSAs.
Specifically, it uses LSA type 10,
and we'll talk about this in more detail a little bit later.
Now, as we mentioned, we can also use BGP.
Specifically, we use something called BGP-LU, or labeled
unicast.
Another option is to use an SDN controller.
SDN, if you're not familiar, is software-defined networking.
And what this does most commonly is facilitates
that multidomain SRTE, which is the segment routing
traffic engineering.
For that multidomain function, it's
going to use BGP-LS, or link state,
and it uses something called PCEP, or path computation
element protocol.
So as an example, we could have a situation here where
we have a controller, which can be something as simple
as an iOS XR router.
Then the other devices connect to this using PCEP.
So these connections would be using that protocol.
Now, the individual devices have names as well.
The controller is actually called
the PCE, which is the path computation element,
and the clients are PCCs, which are your path computation
clients.
So this is how this entire SDN system works.
And, again, keep in mind that this is mostly
used for traffic engineering.
We'll be taking a much deeper look at all of these elements
and how this whole system works when we get to our skill
on segment routing traffic engineering.
So let's focus in a little bit more
on the changes we need to do our routing protocols.
So for IS-IS, it is going to support both IPv4 and IPv6.
As we mentioned, it uses new TLVs, or type-length-values,
for that SID advertisement.
Specifically, it can handle prefix SIDS, adjacency SIDS,
and prefix-to-SID mappings.
This is fully supported with both level 1 and level 2 IS-IS
routing, and it can handle PHP, which is
your penultimate hop popping.
Or it can also handle explicit null,
which is, of course, if you disable PHP.
But IS-IS can fully support both,
whether that's enabled on the MPLS stack or not.
OSPF is going to be modified in a very similar way.
However, it does have a few differences.
First, it only supports IPv4, at least right now.
Of course, things will change.
I'm sure that OSPF version 3 will be supported
at some point, but at the time of this recording,
it's currently not.
Now, this does, of course, use OSPF extensions.
We mentioned that it uses opaque LSAs, specifically type 10,
and then it can be used for your prefix
SIDs and your adjacency SIDs.
These, by the way, are carried in different subtypes
of the type 10.
We'll see that in a lot more detail
when we get to our implementation skill.
We see this on the command line, and we actually
dig into the OSPF database a bit.
So they're all LSA type 10s, but then there's
subtypes under that that carry the different types of SIDs
that we need here for segment routing.
Now, sort of along the same lines as supporting level 1
level 2 in IS-IS, this also fully
supports multiarea from an OSPF perspective,
and it also supports PHP and explicit null.
So those things are the same.
And, as we mentioned, BGP can also
be used to support segment routing.
We use a BGP prefix SID.
This is generally used between BGP domains
to establish a full label switch path.
Remember, that wouldn't normally be
possible outside of a single IGP.
That would break the label switch path.
The segment is then attached to the BGP prefix,
and this, of course, will have to be
global within the entire SR domain, meaning
not just within, of course, an IGP,
because now we're joining multiple IGPs together,
or multiple IGP domains together.
So this is going to have to be unique across everything.
We also have a feature where we support peering segments
for egress peer engineering, or EPE.
This is used within a BGP domain to control outbound traffic.
So this is to choose which exit you
wish to use when going into another BGP environment.
In this category, there are three families.
We have the peer node segment, the peer adjacency segment,
and the peer set segment.
Now, keep in mind, those are all peer segments.
They're just different types of peer segments.
That peer segment is then going to be
used to steer that traffic over specific links
to another BGP peer.
That's why it's a peer segment.
As of right now, there are currently three peering segment
identifiers defined.
We have the peer node SID, which is used
to forward on any interface.
We have the peer adjacency SID, which
is only used to forward on the related interface.
And then we have the peer set SID,
which is used to forward on any interface to a set of peers.
So in this video, we took a closer look at the changes
to the control plane for segment routing.
Specifically, we talked about how IS-IS and OSPF have both
been modified or updated to support carrying
labels for segment routing.
We also talked about how we could use an SDN controller
for this, which, by the way, can be something
as simple as running it on iOS XR,
and we will be doing that in a future skill.
But the next thing we need to look at
are the different segment types.
We've been talking a whole lot about SIDs,
but it's time to focus in on some of those different types.
And that's exactly what we're going to be covering next.
Until then, I hope this has been informative for you,
and I'd like to thank you for viewing.