Network statements in EIGRP are great.
However, they're not so great when one network statement
includes more interfaces than we intended.
We're going to fix that with a feature called
passive interface.
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And that's our objective for this video,
to identify why we would need this feature
and then to verify, when we use it, that it's working.
So let's use this topology and R4 as an example.
R4 has, on this interface, 2/0.
It is the 10.0.24 network. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
It is the 10.0.24 network.
And then off of 4/1, which is a fast ethernet connection,
it's got network 10.0.34.0.
And then over here on the right hand side,
its gig 00 interface is 10.0.4.0.
So any EIGRP, if we went into router,
EIGRP would put the autonomous system number.
And we use the network statement like network 10.0.0.0 WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And we use the network statement like network 10.0.0.0
with a wildcard mask of 0.0.255.
That 255, that's going to include all three interfaces.
And if we don't want this interface included, too bad.
It's coming in with this network statement.
And we could be more granular with our network statements.
But another option, if we have lots of interfaces
that start with 10.0 and we want to exclude this one, what
we can do is go into router EIGRP
and simply specify passive interface, fast ethernet, 4/1.
And it'll make that interface no longer send or receive WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And it'll make that interface no longer send or receive
updates or hello messages.
It basically won't participate for that interface
in EIGRP even though the network statement would otherwise say,
yes, you're invited to the party.
So here, on router 4, let's go ahead and verify,
show ip eigrp interfaces just to verify our EIGRP enabled
interfaces.
And here it shows us we have four interfaces that
are participating in EIGRP.
And if we want to see how they got there,
we could do a show ip protocols.
That'll give us some really good insight as to why.
Here's the command, show ip protocols, great.
And down here is showing us that we WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And down here is showing us that we
have a network statement that prop those four
interfaces into EIGRP.
So if we wanted to go ahead and take
one of those out, the interface 4/1,
let's verify that real quick with the other show ip
eigrp interface.
And we did a show ip eigrp neighbors.
We've got neighbors hanging off of three of those interfaces
including fast ethernet 4/1.
So let's specify interface Fa4/1 as passive
from EIGRP's perspective.
What we'll do is go into configuration mode and router WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
What we'll do is go into configuration mode and router
eigrp 1.
And then we'll simply say passive interface.
And one of the options here is default.
And passive interface default says, hey, by default
regards to the network statement,
all the interfaces are going to be passive by default
unless specifically specified otherwise.
In this case, we don't want to do default. All the interfaces,
we just want to do passive interface for fast ethernet.
And it is 4/1.
Great.
So we're going to lose a neighbor.
That's R3 across the way.
And now if we do a show ip eigrp interface and press Enter, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And now if we do a show ip eigrp interface and press Enter,
now we have those three interfaces left.
And if we do a show IP protocols and press Enter,
this is specifying here in the output of show IP protocols
that we have a passive interface.
And that can be handy if we need to remember, oh,
why isn't fast ethernet 4/1 participating in EIGRP?
It's got a network interface that begins with 10,
and our network statement supported it.
Why isn't it?
And the answer here is, because we've specified it
to be passive in router config.
So the concept of passive interface
applies to many routing protocols including
RIP and OSPF, where if we don't want a specific interface WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
RIP and OSPF, where if we don't want a specific interface
to participate, we can just go ahead and use
a passive statement for that interface.
And that interface will no longer
participate as part of the routing protocol.
So in this video and demonstration,
we've now identified that if we are running a network statement
and it includes multiple interfaces,
and one or two of those we don't want included,
we can use a passive interface statement
for those specific interfaces to basically kick them out
of the party.
I hope this has been informative for you.
And I'd like to thank you for viewing.