Welcome to the video.
My name is Keith Barker.
And I have a dear friend named Kevin
who has a podcast with a fantastic name.
The name is The Broadcast Storm.
I love it, because if we have a Layer 2 environment that
has loops, and Spanning Tree hasn't
done its job in identifying the loops and preventing it,
a broadcast can just loop and loop and loop and loop
forever at very, very high speed.
So in this video, I'd like to share with you some protections
that we can use against that, called storm control,
in a Catalyst switched environment.
So let's imagine we have switch 1 and switch 2 here. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So let's imagine we have switch 1 and switch 2 here.
It looks like there's a trunk there.
Let's put another trunk in.
I'll put a trunk right there.
Great.
So we have two trunks.
And let's say, for a VLAN, number 10,
that we have disabled Spanning Tree.
And we just told the switch, don't
worry about Spanning Tree for VLAN 10.
It's going to be OK through some misconfiguration.
Well, a user, in VLAN 10, if they send an ARP request
or do anything else that involves a broadcast
layer to broadcast, that broadcast
will go in the switch, and then it's
going to be forwarded, because in VLAN 10, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
going to be forwarded, because in VLAN 10,
the trunks that are associated with VLAN 10
is going to be sent out the trunks, who
are going to forward it back down to the other trunks.
And that's going to loop in both directions
for a long, long time.
Now, there's good news and bad news of this.
The good news is that you have these fairly
high-powered switches that do allow switching in hardware,
and they can forward like millions of frames per second.
However, our users are going to have a really bad experience,
because we could consume almost all the bandwidth and resources
on these switches just by having the loops that are in place.
So we might ask ourselves, well, what can be done? WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So we might ask ourselves, well, what can be done?
Well, number one is turn on Spanning Tree,
so this won't happen.
And then secondly to protect our networks
against this situation, where we might have a broadcast
storm that's just looping, looping, then going around
and around, what we could do is use
the feature called storm control in a Catalyst Cisco
environment.
So I took the liberty of labbing up three physical switches.
And they're connected on these ports respectively.
And currently, I have VLAN 1 and VLAN 10 and VLAN 20.
And what I propose we do in this little lab
environment, this little closed loop, is let's go ahead WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
environment, this little closed loop, is let's go ahead
and disable Spanning Tree for VLAN 1,
and then send a broadcast like to an ARP request,
and then just see the lights just go crazy
and utilization go crazy, because there's
nothing to prevent the Layer 2 loop from happening.
So we'll introduce the problem.
And then the great news is that we'll look at storm control
as a method of helping to survive that broadcast
storm while it happens and not have the whole network
go belly up.
All right, so I'm using SecureCRT.
I have three sessions open.
I have the command window that sends
one command to all windows. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
one command to all windows.
So let's verify our connections to begin with.
Do a show cdp neighbor.
So from switch 1's perspective, we are connected down
to switch 2 off of Fast Ethernet 0/3,
and we're connected to switch 3 on Fast Ethernet 0/4.
Let's verify that against our topology.
Sure enough, 0/3 and 0/4 to 2 and 3 respectively.
And then let's also go down to switch 2 just
make sure that that port 0/5 goes over to switch 3.
So if we go to switch 2, and it says that switch 3
is connected off of its Fast Ethernet 0/5. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
is connected off of its Fast Ethernet 0/5.
That looks fantastic.
Let's also verify Spanning Tree is running.
Show Spanning Tree for VLAN 1.
And switch 3 has a root port and a block port.
Switch 1 is the root.
Both of its ports are designated.
And switch 3 has a root port and a designated port going over
to switch 2.
So currently, we're not going to have a whole bunch of loops,
because we have Spanning Tree that's
protecting against loops.
But let's do this.
Let's go ahead and do a config t, and no Spanning
Tree for VLAN 1. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Tree for VLAN 1.
And let's go to a device, like switch 1,
and do a config t, interface VLAN 1, IP address.
And let's do a ping out to 1.1.1.88.
It doesn't exist, but all we're after is the actual ARP
request.
And I'm looking over my shoulder.
Let me see if I can get this in frame.
Let me walk over here.
So these LEDs right here are just all lit up.
So we have a Layer 2 loop that's currently happening.
So if we do show interface, let's go ahead
and pick on Fast Ethernet 0/3. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
and pick on Fast Ethernet 0/3.
So show interface FA 0/3.
Here, it says we've had 47,233 broadcasts.
If we hit the up arrow key again, and do a pipe,
and just say include Received, press Enter, now it's
at 58,000.
Yeah, it's climbing pretty quick.
So we have an opportunity right now
to help protect the switch against a broadcast storm.
Now, storm control isn't just for broadcasts.
It's also used unicast and multicast.
And let me walk you through setting it up.
And I'll talk with you about some options WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And I'll talk with you about some options
how it's set up and then what they mean as we implement it.
So let's do a show interface status.
So let's do both interfaces 3 and 4 here on switch 1,
interface range, Fast Ethernet 0/3 through four.
And the syntax is storm-control, and it'll do a question mark.
And we can specify that we want it
for broadcast traffic or multicast traffic or unicast
traffic.
And let's start off with broadcast.
So we specified broadcast, and then we're WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So we specified broadcast, and then we're
going to specify a level.
This is a level which, if it's hit,
this switch will then start going ahead and dropping
or suppressing any broadcasts above that level.
Now, it doesn't actually stop everything,
because if you have CDP messages and Spanning Tree BPDUs,
those are still allowed through, because that's our control
plane.
However, the general broadcast traffic outside of that
would be limited.
So we use the keyword level and then a question mark.
And here we can specify the level.
So we can specify a percentage of the bandwidth
on that interface, or we can specify WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
on that interface, or we can specify
a threshold based on bits per second,
or a threshold based on packets per second.
The choice is totally yours.
So I'm going to go ahead and say 10%.
I don't want anything higher than 10% regarding broadcast
before we start suppressing it.
And then if we want to, to we just press Enter.
And then if it goes over 10, it'll start suppressing.
And if it goes under 10, it'll stop suppressing.
So if we do a question mark, we can also
specify a falling threshold.
So here we could say 5.
So what this means if we got to 10% of our available bandwidth
on that interface, we could go ahead and start suppressing WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
on that interface, we could go ahead and start suppressing
broadcasts, and we'd continue to suppress
until we dropped down to 5, at which time it would relax.
And then we'll press Enter.
And we can do the same thing for other types of traffic,
too, including multicast.
Let's say bits per second.
And let's say 10K.
And then for the following threshold, let's say 5K.
And let's do one more, except this time,
we'll do it for unicast.
And this time, we want to make sure our unicast traffic makes WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And this time, we want to make sure our unicast traffic makes
it.
So I'm going to say 85%, and then
go ahead and stop suppressing once it gets down to 80.
Then we also have the option of setting up the violation.
Now, by default, the violation is just
to restrict that additional type of traffic.
However, we can specify action.
And then we have two options.
One is shutdown, which is an error disable
state for that port.
And the other option is sending an SNMP Trap.
So I'm going to leave the default of just suppressing it
down to the levels we specified.
And then if we do a show storm control, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And then if we do a show storm control,
press Enter, here, it's showing that storm control's
enabled on both those ports.
I have an upper limit of 10, a lower limit of 5.
And there's our current utilization
based on that one ARP request that I
sent into the switch a few minutes ago.
Another thing that's important to know
is that if we want to see the details for each one,
we could do a show storm control for a specific interface
or just for broadcasts by adding the broadcast option.
And that's what it shows by default.
But if we got rid of the broadcast and said, unicast,
it would show us that information.
And if we said, multicast, it would show us that information. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And if we said, multicast, it would show us that information.
So at the moment, not a whole bunch of unicast or multicast
going on, but we do have quite a bit of broadcast
based on the ARP request I sent.
So the appropriate thing to do here
to get it back under control would
be to go into configuration mode and turn
on Spanning Tree for VLAN 1, which would go ahead and stop
the madness.
Because as Spanning Tree converges,
there will no longer be a Layer 2 loop.
So thanks for joining me in this video regarding storm control.
In the next video, we'll take a look at root guard
to help protect our environment against unwanted Spanning Tree WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
to help protect our environment against unwanted Spanning Tree
topology changes.
So I'll see you there in just a moment.
Meanwhile, I hope this has been informative for you.
And I'd like to thank you for viewing.