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Welcome to the video.

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My name is Keith Barker.

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And I have a dear
friend named Kevin

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who has a podcast
with a fantastic name.

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The name is The Broadcast Storm.

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I love it, because if we have
a Layer 2 environment that

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has loops, and
Spanning Tree hasn't

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done its job in identifying
the loops and preventing it,

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a broadcast can just loop
and loop and loop and loop

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forever at very,
very high speed.

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So in this video, I'd like to
share with you some protections

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that we can use against
that, called storm control,

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in a Catalyst
switched environment.

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So let's imagine we have
switch 1 and switch 2 here.
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So let's imagine we have
switch 1 and switch 2 here.

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It looks like there's
a trunk there.

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Let's put another trunk in.

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I'll put a trunk right there.

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Great.

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So we have two trunks.

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And let's say, for
a VLAN, number 10,

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that we have disabled
Spanning Tree.

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And we just told
the switch, don't

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worry about Spanning
Tree for VLAN 10.

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It's going to be OK through
some misconfiguration.

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Well, a user, in VLAN 10,
if they send an ARP request

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or do anything else that
involves a broadcast

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layer to broadcast,
that broadcast

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will go in the
switch, and then it's

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going to be forwarded,
because in VLAN 10,
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going to be forwarded,
because in VLAN 10,

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the trunks that are
associated with VLAN 10

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is going to be sent
out the trunks, who

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are going to forward it back
down to the other trunks.

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And that's going to
loop in both directions

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for a long, long time.

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Now, there's good news
and bad news of this.

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The good news is that
you have these fairly

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high-powered switches that do
allow switching in hardware,

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and they can forward like
millions of frames per second.

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However, our users are going to
have a really bad experience,

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because we could consume almost
all the bandwidth and resources

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on these switches just by having
the loops that are in place.

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So we might ask ourselves,
well, what can be done?
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So we might ask ourselves,
well, what can be done?

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Well, number one is
turn on Spanning Tree,

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so this won't happen.

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And then secondly to
protect our networks

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against this situation, where
we might have a broadcast

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storm that's just looping,
looping, then going around

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and around, what
we could do is use

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the feature called storm
control in a Catalyst Cisco

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environment.

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So I took the liberty of labbing
up three physical switches.

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And they're connected on
these ports respectively.

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And currently, I have VLAN
1 and VLAN 10 and VLAN 20.

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And what I propose we
do in this little lab

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environment, this little
closed loop, is let's go ahead
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environment, this little
closed loop, is let's go ahead

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and disable Spanning
Tree for VLAN 1,

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and then send a broadcast
like to an ARP request,

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and then just see the
lights just go crazy

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and utilization go
crazy, because there's

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nothing to prevent the
Layer 2 loop from happening.

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So we'll introduce the problem.

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And then the great news is that
we'll look at storm control

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as a method of helping
to survive that broadcast

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storm while it happens and
not have the whole network

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go belly up.

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All right, so I'm
using SecureCRT.

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I have three sessions open.

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I have the command
window that sends

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one command to all windows.
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one command to all windows.

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So let's verify our
connections to begin with.

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Do a show cdp neighbor.

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So from switch 1's perspective,
we are connected down

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to switch 2 off of
Fast Ethernet 0/3,

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and we're connected to switch
3 on Fast Ethernet 0/4.

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Let's verify that
against our topology.

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Sure enough, 0/3 and 0/4
to 2 and 3 respectively.

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And then let's also go
down to switch 2 just

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make sure that that port
0/5 goes over to switch 3.

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So if we go to switch 2,
and it says that switch 3

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is connected off of
its Fast Ethernet 0/5.
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is connected off of
its Fast Ethernet 0/5.

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That looks fantastic.

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Let's also verify
Spanning Tree is running.

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Show Spanning Tree for VLAN 1.

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And switch 3 has a root
port and a block port.

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Switch 1 is the root.

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Both of its ports
are designated.

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And switch 3 has a root port
and a designated port going over

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to switch 2.

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So currently, we're not going
to have a whole bunch of loops,

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because we have
Spanning Tree that's

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protecting against loops.

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But let's do this.

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Let's go ahead and do a
config t, and no Spanning

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Tree for VLAN 1.
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Tree for VLAN 1.

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And let's go to a
device, like switch 1,

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and do a config t, interface
VLAN 1, IP address.

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And let's do a ping
out to 1.1.1.88.

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It doesn't exist, but all
we're after is the actual ARP

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request.

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And I'm looking
over my shoulder.

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Let me see if I can
get this in frame.

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Let me walk over here.

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So these LEDs right here
are just all lit up.

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So we have a Layer 2 loop
that's currently happening.

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So if we do show
interface, let's go ahead

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and pick on Fast Ethernet 0/3.
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and pick on Fast Ethernet 0/3.

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So show interface FA 0/3.

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Here, it says we've
had 47,233 broadcasts.

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If we hit the up arrow
key again, and do a pipe,

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and just say include Received,
press Enter, now it's

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at 58,000.

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Yeah, it's climbing
pretty quick.

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So we have an
opportunity right now

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to help protect the switch
against a broadcast storm.

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Now, storm control isn't
just for broadcasts.

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It's also used
unicast and multicast.

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And let me walk you
through setting it up.

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And I'll talk with
you about some options
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And I'll talk with
you about some options

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how it's set up and then what
they mean as we implement it.

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So let's do a show
interface status.

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So let's do both interfaces
3 and 4 here on switch 1,

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interface range, Fast
Ethernet 0/3 through four.

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And the syntax is storm-control,
and it'll do a question mark.

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And we can specify
that we want it

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for broadcast traffic or
multicast traffic or unicast

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traffic.

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And let's start
off with broadcast.

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So we specified
broadcast, and then we're
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So we specified
broadcast, and then we're

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going to specify a level.

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This is a level
which, if it's hit,

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this switch will then start
going ahead and dropping

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or suppressing any
broadcasts above that level.

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Now, it doesn't actually
stop everything,

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because if you have CDP messages
and Spanning Tree BPDUs,

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those are still allowed through,
because that's our control

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plane.

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However, the general broadcast
traffic outside of that

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would be limited.

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So we use the keyword level
and then a question mark.

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And here we can
specify the level.

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So we can specify a
percentage of the bandwidth

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on that interface,
or we can specify
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on that interface,
or we can specify

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a threshold based
on bits per second,

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or a threshold based
on packets per second.

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The choice is totally yours.

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So I'm going to go
ahead and say 10%.

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I don't want anything higher
than 10% regarding broadcast

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before we start suppressing it.

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And then if we want to,
to we just press Enter.

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And then if it goes over
10, it'll start suppressing.

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And if it goes under 10,
it'll stop suppressing.

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So if we do a question
mark, we can also

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specify a falling threshold.

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So here we could say 5.

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So what this means if we got to
10% of our available bandwidth

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on that interface, we could
go ahead and start suppressing
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on that interface, we could
go ahead and start suppressing

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broadcasts, and we'd
continue to suppress

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until we dropped down to 5,
at which time it would relax.

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And then we'll press Enter.

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And we can do the same thing
for other types of traffic,

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too, including multicast.

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Let's say bits per second.

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And let's say 10K.

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And then for the following
threshold, let's say 5K.

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And let's do one more,
except this time,

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we'll do it for unicast.

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And this time, we want to make
sure our unicast traffic makes
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And this time, we want to make
sure our unicast traffic makes

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it.

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So I'm going to
say 85%, and then

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go ahead and stop suppressing
once it gets down to 80.

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Then we also have the option
of setting up the violation.

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Now, by default, the
violation is just

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to restrict that
additional type of traffic.

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However, we can specify action.

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And then we have two options.

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One is shutdown, which
is an error disable

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state for that port.

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And the other option is
sending an SNMP Trap.

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So I'm going to leave the
default of just suppressing it

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down to the levels we specified.

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And then if we do a
show storm control,
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And then if we do a
show storm control,

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press Enter, here, it's
showing that storm control's

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enabled on both those ports.

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I have an upper limit of
10, a lower limit of 5.

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And there's our
current utilization

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based on that one
ARP request that I

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sent into the switch
a few minutes ago.

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Another thing that's
important to know

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is that if we want to see
the details for each one,

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we could do a show storm
control for a specific interface

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or just for broadcasts by
adding the broadcast option.

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And that's what it
shows by default.

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But if we got rid of the
broadcast and said, unicast,

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it would show us
that information.

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And if we said, multicast, it
would show us that information.
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And if we said, multicast, it
would show us that information.

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So at the moment, not a whole
bunch of unicast or multicast

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07:36.110 --> 07:38.480 align:middle line:90%
going on, but we do have
quite a bit of broadcast

200
07:38.480 --> 07:39.813 align:middle line:84%
based on the ARP request I sent.

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07:39.813 --> 07:41.272 align:middle line:90%
So the appropriate
thing to do here

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07:41.272 --> 07:42.830 align:middle line:90%
to get it back
under control would

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07:42.830 --> 07:45.090 align:middle line:90%
be to go into
configuration mode and turn

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07:45.090 --> 07:48.230 align:middle line:90%
on Spanning Tree for VLAN 1,
which would go ahead and stop

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07:48.230 --> 07:49.100 align:middle line:84%
the madness.

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07:49.100 --> 07:50.780 align:middle line:90%
Because as Spanning
Tree converges,

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07:50.780 --> 07:53.070 align:middle line:90%
there will no longer
be a Layer 2 loop.

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07:53.070 --> 07:56.480 align:middle line:90%
So thanks for joining me in this
video regarding storm control.

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07:56.480 --> 07:58.880 align:middle line:90%
In the next video, we'll
take a look at root guard

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07:58.880 --> 08:01.850 align:middle line:90%
to help protect our environment
against unwanted Spanning Tree
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

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07:58.880 --> 08:01.850 align:middle line:90%
to help protect our environment
against unwanted Spanning Tree

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08:01.850 --> 08:02.780 align:middle line:84%
topology changes.

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08:02.780 --> 08:04.860 align:middle line:90%
So I'll see you there
in just a moment.

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08:04.860 --> 08:07.340 align:middle line:90%
Meanwhile, I hope this has
been informative for you.

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08:07.340 --> 08:10.690 align:middle line:90%
And I'd like to thank
you for viewing.