- [Instructor] In this video,
we want to take a look at a couple of features
that can help us limit some of the EIGRP messages
going throughout our network.
For example, do we really need to send Hello messages
out of R1s gigabit zero slash one interface?
I mean, there's no other EIGRP speaking router
off of that interface.
Same thing for R3s gigabit zero slash two interface.
Would I really need to send Hello messages
out of that interface for EIGRP?
I'm going to say no.
In fact, that might be a security concern.
If we don't have authentication configured,
then we might have some rogue router out there
that's trying to form a neighborship with us
and inject incorrect routes.
So this could help with performance,
it could help with security to just not send Hellos
out of those interfaces.
And remember when we discussed the concept
of sending out queries,
we said that OSPF is going to have its successor route.
And we might have a backup path
that we can switch over to almost instantaneously
within just a couple of seconds or so.
And that backup path was called a feasible successor route.
But we might have another route
that would legitimately get us to a destination,
but it had failed the feasibility condition.
And in response to that,
the router is going to send queries
throughout the network saying,
Hey, does anybody else know how to get to this network?
Well, in a topology like this,
we can see that gigabit zero slash one on R1,
there's no way it's going to come back
and get us to any other network,
it's just connecting out to end devices.
Same thing with gigabit zero slash two on R3.
So those routers are not just configured on one router,
but those routers, they might be good candidates
to be Stub routers.
A Stub router is a router that we will not send
an EIGRP query to.
So what we're doing is we're limiting the scope
of the queries.
Now, is R1 going to advertise anything back to R2
if it's a stub router?
By default, it will advertise any directly connected routes,
and any summary routes that it knows about.
But we can adjust what gets advertised
if anything back to R2.
Let's take a look at the configuration
for both of those.
Beginning on R1,
let's go into router configuration mode
for EIGRP autonomous system one,
and first let's make gigabit zero slash one
a passive interface.
I'll say passive hyphen interface gig zero slash one.
That's going to suppress the sending of EIGRP
Hello messages out of gigabit zero slash one.
Now that does not mean that we'll not be advertising
of that network off of gig zero slash one,
we'll still advertise the 10 dot one dot one
dot zero slash 24 network.
However, we just won't be trying to form a neighborship
off of that interface.
Now let's set up stub routing.
I'll say EIGRP stub,
and if I just press Enter right now,
we're going to be advertising any directly connected
and summary routes.
So in our case,
we should see a 10 dot one dot one dot zero slash 24
show up on R2.
Let's confirm that, I'll just press enter.
Let's go to R2.
You notice the neighborship gets reset when we do that.
And if I do a show IP route,
we do indeed see 10 dot one dot one dot zero,
so it did get advertised.
And we can dig into our neighbors configuration
and see if it is a stub router.
And if it is, what is it advertising to us?
We can do a show IP EIGRP neighbors detail command.
And for our neighbor of 172 dot 16 dot one dot one,
that's R1, we see that it is a stub peer
and it is advertising the connected routes,
such as 10 dot one dot one dot zero slash 24
and any summary routes.
Now we don't have any of those,
but if we did, those would be advertised as well.
Now let's take a look at how we could limit
what gets advertised via a stub router.
Let's take a look at some context sensitive help.
Instead of saying just EIGRP stub,
we could do some other things.
I could say connected and that would,
that would only give me connected routes.
I could say leak map and this might be useful
if I'm really not just hanging off by myself
going out to end users.
If I really am getting routes from somewhere else.
I might not want to have those routes
sent into the EIGRP autonomous system.
But I might want certain routes to get through,
maybe to get to a single server as an example.
So what I could do is create a leak map.
Here's how that works.
You create an access control list
to identify the IP address or the network
that you want to be advertised to R2,
that you want to "leak" to R2.
You then take that IP access list
and you reference it in a route map.
You would say inside of your route map
that you wanted to match IP address
and give the number or the name
of your access control list.
Then when you're configuring stub routing,
you would say,
leak map, and you would put in
your route map name right here.
Or if I didn't want to advertise any routes
out to my neighbor,
I could say receive only.
In fact, let's do that.
If I say,
receive only it'll reset our neighborship.
Let's go back to R2 see what we've learned now.
Let's do a show IP route.
And 10 dot one dot one dot zero is gone,
because it's no longer being advertised by R1.
What other options do we have?
We could say if I'm getting a route
that was redistributed into my EIGRP autonomous system,
I'll advertise that or any statically configured routes,
or any summary routes.
So those are our options for making a router
an EIGRP stub router.
Again, the main goal for both of these things that we did,
the passive interface and the stub configuration,
we're trying to suppress the sending of any
unnecessary EIGRP packets.
This could be both for network performance
as well as security.