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[MUSIC PLAYING]

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Next up, let's have a quick
discussion about NSF and NSR.

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This is Non-Stop Forwarding
and Non-Stop Routing.

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Both of these sort
of do the same job.

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Although, NSR does it in
a slightly different way.

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And because they're basically
doing the same thing,

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we really don't need both.

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So we're going to be
using one or the other,

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where NSR is sort of
the newer way to do it.

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So let's jump in and
take a look at some

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of the details on these.

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And then we'll take a look
at what the defaults are

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on IOS XE and IOS XR.

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So Non-Stop Forwarding
and Non-Stop Routing

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are both here to pretty much
handle the exact same issue.

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Again, they're both technologies
that aid with stability,

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or you could say, convergence
during route processor

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switchovers.

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So if you have a router with
multiple route processors,

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one of them fails, and we
failover to the other one.

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These two technologies
help with the stability

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of things like our database
and our neighborship

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during that failover.

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So let's start by talking
about Non-Stop Forwarding.

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Non-Stop Forwarding has been
around for quite some time.

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And what this does is it
allows that forwarding

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to continue using
already known routes.

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So routes that are installed
on our neighbors, routes

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that are installed on our local
line cards, things like this,

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we continue forwarding traffic.

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Now, there are two
versions of this.

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There is a Cisco version, which
pretty much came along first.

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And then the IETF released
an industry standard version

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so that other vendors could
participate in this as well.

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Now, NSF routers generally
fall into three categories.

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The first is an
NSF capable router.

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You could say this is
the router actually doing

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the non-stop forwarding.

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One of its
requirements is it has

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to have dual route processors.

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If there aren't
redundant processors,

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well then there's
nothing to failover too.

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And if we lose our
route processor,

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well then we're just down.

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One of its jobs then is to
relearn the OSPF neighbors

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without causing any
neighbor resets.

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We don't want our neighbors
to completely wipe out

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their databases with
our information,

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and have our
neighbors start over.

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It's then going to reaquire
the link state database.

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In order for all
of this to work,

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it uses signaling,
which is actually

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done with a link local
LSA to the other routers,

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telling them that a
failover is occurring.

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Now, in order for
that to work, we

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need our second
category of routers,

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which is the NSF aware routers.

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These are routers that are
going to actually recognize

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that signal coming from
the failing router.

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So, the router above.

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What they're going to
do in response to this

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is they're going to
preserve the OSPF link state

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database, as well as
their own routing tables.

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We also allow the failing router
to rebuild its neighborships,

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again, without
doing a full reset.

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The whole idea here is we
rebuild everything with OSPF

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while we are continuing to use
the old information that we

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had from OSPF.

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Now, the third type
of router is one

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that is simply not NSF aware.

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And the problem with
this is, of course, it's

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not going to participate
in NSF at all.

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And after this
failover occurs, we're

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going to have to just
reconverge OSPF the normal way.

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We're going to have to
re-establish neighborships,

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re-exchange databases.

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They're just not
participating in NSF.

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Now, in fairness, most
routers today do support NSF.

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Again, they may
not all be capable

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because they don't have
dual route processors.

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But most routers are NSF aware.

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The big question we
have to worry about

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is, are they IETF aware or
are they Cisco only aware?

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And that could
affect our decisions

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as far as what to use.

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So the second technology here
is NSR, or Non-Stop Routing.

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This also allows for the
failover process restart

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or in-service software update,
without affecting neighbors.

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And this is where NSR is
a bit better than NSF.

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This uses something called
warm standby extensions, which

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essentially runs a standby
OSPF process on the standby RP.

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That is then kept synchronized
with the OSPF process

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on the primary RP.

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So now, when there's
an RP failover,

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the standby OSPF process simply
takes over on the standby RP,

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and we keep going as if
nothing ever happened.

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That's why this does not
affect the neighbors.

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That makes this a
better solution.

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Because now, the
neighbors don't have

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to be NSR aware, or NSF
capable, or anything else.

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This is all done in-house
on this NSR capable router.

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And again, since this
does the exact same job,

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but does it in-house,
this completely

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alleviates the
requirement for NSR.

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We don't need to have
both at the same time.

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So let's take a look at
these on the command line.

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We'll look at the
topology real briefly,

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just to see which routers
we're going to look at.

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But it really doesn't matter
where they are in the topology.

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We're just going to be looking
at their default settings.

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So we are going to want to
look at both IOS XR and IOS XE.

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So we will simply be
taking a look at Router 1,

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which is running IOS XR.

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And then we'll look at Router
5, which is running IOS XE.

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So we'll start by taking
a look at Router 1.

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So real simply here on Router
1, we'll do a show IP OSPF.

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And we see right here,
that it says NSR Non-Stop

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Routing is enabled.

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So this feature is enabled
by default on IOS XR.

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Since this supports NSR, there
would really be no reason

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to ever go back to NSF.

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However, that
feature is available

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if you wanted to enable it.

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Now let's take a
look at Router 5.

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Again, if we do
our show IP OSPF,

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this actually lists it down
towards the bottom more.

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But we can see here
that the IETF NSF helper

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support is enabled, as well as
the Cisco NSF helper support.

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Now, the helper support means
that this router is NSF aware.

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This router, of course,
is not NSF capable

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because it does not have
dual route processors.

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Since it doesn't have
dual route processors,

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there's also really no
good reason to turn on NSR.

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However, if you do
need it or want it just

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to look at it for
whatever reason,

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you can certainly turn it on.

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Simply go into router
OSPF and type NSR.

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It'll now be enabled.

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We do our show epos OSPF again.

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We see here now, Non-Stop
Routing is enabled.

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Again, it won't actually
do anything on this router

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because this router is not a
dual route processor device.

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In this video, we
talked about two, well,

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sort of competing
or redundant things

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that we can do on our routers
to aid in the event of a route

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processor failover.

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The first is NSF, or
Non-Stop Forwarding,

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which actually
involves the neighbors,

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and has them basically
negotiate this capability,

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so that we can keep forwarding
traffic in the event of a route

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process switchover.

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Then we looked at NSR, its
newer replacement, if you will,

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that allows it to do
all of that in-house.

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It simply fails over to
the other route processor,

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keeps right on going
as if nothing happened.

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Not affecting the
neighbors at all.

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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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