[MUSIC PLAYING]
Next up, let's have a quick discussion about NSF and NSR.
This is Non-Stop Forwarding and Non-Stop Routing.
Both of these sort of do the same job.
Although, NSR does it in a slightly different way.
And because they're basically doing the same thing,
we really don't need both.
So we're going to be using one or the other,
where NSR is sort of the newer way to do it.
So let's jump in and take a look at some
of the details on these.
And then we'll take a look at what the defaults are
on IOS XE and IOS XR.
So Non-Stop Forwarding and Non-Stop Routing
are both here to pretty much handle the exact same issue.
Again, they're both technologies that aid with stability,
or you could say, convergence during route processor
switchovers.
So if you have a router with multiple route processors,
one of them fails, and we failover to the other one.
These two technologies help with the stability
of things like our database and our neighborship
during that failover.
So let's start by talking about Non-Stop Forwarding.
Non-Stop Forwarding has been around for quite some time.
And what this does is it allows that forwarding
to continue using already known routes.
So routes that are installed on our neighbors, routes
that are installed on our local line cards, things like this,
we continue forwarding traffic.
Now, there are two versions of this.
There is a Cisco version, which pretty much came along first.
And then the IETF released an industry standard version
so that other vendors could participate in this as well.
Now, NSF routers generally fall into three categories.
The first is an NSF capable router.
You could say this is the router actually doing
the non-stop forwarding.
One of its requirements is it has
to have dual route processors.
If there aren't redundant processors,
well then there's nothing to failover too.
And if we lose our route processor,
well then we're just down.
One of its jobs then is to relearn the OSPF neighbors
without causing any neighbor resets.
We don't want our neighbors to completely wipe out
their databases with our information,
and have our neighbors start over.
It's then going to reaquire the link state database.
In order for all of this to work,
it uses signaling, which is actually
done with a link local LSA to the other routers,
telling them that a failover is occurring.
Now, in order for that to work, we
need our second category of routers,
which is the NSF aware routers.
These are routers that are going to actually recognize
that signal coming from the failing router.
So, the router above.
What they're going to do in response to this
is they're going to preserve the OSPF link state
database, as well as their own routing tables.
We also allow the failing router to rebuild its neighborships,
again, without doing a full reset.
The whole idea here is we rebuild everything with OSPF
while we are continuing to use the old information that we
had from OSPF.
Now, the third type of router is one
that is simply not NSF aware.
And the problem with this is, of course, it's
not going to participate in NSF at all.
And after this failover occurs, we're
going to have to just reconverge OSPF the normal way.
We're going to have to re-establish neighborships,
re-exchange databases.
They're just not participating in NSF.
Now, in fairness, most routers today do support NSF.
Again, they may not all be capable
because they don't have dual route processors.
But most routers are NSF aware.
The big question we have to worry about
is, are they IETF aware or are they Cisco only aware?
And that could affect our decisions
as far as what to use.
So the second technology here is NSR, or Non-Stop Routing.
This also allows for the failover process restart
or in-service software update, without affecting neighbors.
And this is where NSR is a bit better than NSF.
This uses something called warm standby extensions, which
essentially runs a standby OSPF process on the standby RP.
That is then kept synchronized with the OSPF process
on the primary RP.
So now, when there's an RP failover,
the standby OSPF process simply takes over on the standby RP,
and we keep going as if nothing ever happened.
That's why this does not affect the neighbors.
That makes this a better solution.
Because now, the neighbors don't have
to be NSR aware, or NSF capable, or anything else.
This is all done in-house on this NSR capable router.
And again, since this does the exact same job,
but does it in-house, this completely
alleviates the requirement for NSR.
We don't need to have both at the same time.
So let's take a look at these on the command line.
We'll look at the topology real briefly,
just to see which routers we're going to look at.
But it really doesn't matter where they are in the topology.
We're just going to be looking at their default settings.
So we are going to want to look at both IOS XR and IOS XE.
So we will simply be taking a look at Router 1,
which is running IOS XR.
And then we'll look at Router 5, which is running IOS XE.
So we'll start by taking a look at Router 1.
So real simply here on Router 1, we'll do a show IP OSPF.
And we see right here, that it says NSR Non-Stop
Routing is enabled.
So this feature is enabled by default on IOS XR.
Since this supports NSR, there would really be no reason
to ever go back to NSF.
However, that feature is available
if you wanted to enable it.
Now let's take a look at Router 5.
Again, if we do our show IP OSPF,
this actually lists it down towards the bottom more.
But we can see here that the IETF NSF helper
support is enabled, as well as the Cisco NSF helper support.
Now, the helper support means that this router is NSF aware.
This router, of course, is not NSF capable
because it does not have dual route processors.
Since it doesn't have dual route processors,
there's also really no good reason to turn on NSR.
However, if you do need it or want it just
to look at it for whatever reason,
you can certainly turn it on.
Simply go into router OSPF and type NSR.
It'll now be enabled.
We do our show epos OSPF again.
We see here now, Non-Stop Routing is enabled.
Again, it won't actually do anything on this router
because this router is not a dual route processor device.
In this video, we talked about two, well,
sort of competing or redundant things
that we can do on our routers to aid in the event of a route
processor failover.
The first is NSF, or Non-Stop Forwarding,
which actually involves the neighbors,
and has them basically negotiate this capability,
so that we can keep forwarding traffic in the event of a route
process switchover.
Then we looked at NSR, its newer replacement, if you will,
that allows it to do all of that in-house.
It simply fails over to the other route processor,
keeps right on going as if nothing happened.
Not affecting the neighbors at all.
I hope this has been informative for you,
and I'd like to thank you for viewing.