Cisco CCNA ICND2 640-816

Switch STP: Configuring Basic STP

by Jeremy Cioara

Start your 7-day free trial today.

This video is only available to subscribers.

A free trial includes:

  • Unlimited 24/7 access to our entire IT training video library.
  • Ability to train on the go with our mobile website and iOS/Android apps.
  • Note-taking, bookmarking, speed control, and closed captioning features.
Video Title Duration

Review: Rebuilding the Small Office Network, Part 1

Review: Rebuilding the Small Office Network, Part 2

Review: Rebuilding the Small Office Network, Part 3

Switch VLANs: Understanding VLANs

Switch VLANs: Understanding Trunks and VTP

Switch VLANs: Configuring VLANs and VTP, Part 1

Switch VLANs: Configuring VLANs and VTP, Part 2

Switch STP: Understanding the Spanning-Tree Protocol

Switch STP: Configuring Basic STP

00:00:00 - Now that we've talked about the concepts behind spanning tree
00:00:03 - protocol, let's get it set up. We're gonna take a look first off
00:00:07 - at our new network diagram. We're going to enhance what our network
00:00:10 - diagram looks like, add some redundant connections, then we will
00:00:13 - look at the, in the current spanning tree protocol configuration,
00:00:17 - because it's already running on all CISCO devices. Let's see
00:00:20 - how it ran, by default. Then we'll tweak it, we'll tune it, we'll
00:00:24 - make it more efficient, and then we'll do some tests. I'm gonna do some ping
00:00:27 - tests and pull some links and see what happens, and how long
00:00:30 - spanning tree takes to fail over. Now before we get going
00:00:34 - into the material, I have to show you something. I have to show
00:00:38 - you this most amazing, coolest thing, I've ever owned in my life.
00:00:42 - You may have heard of the Apple iPhone, right. Well, I got
00:00:46 - one, and you gotta see it. You gotta see this picture I just took
00:00:50 - of it. It is the biggest waste of time I have ever had, but I love
00:00:53 - it and I can't stop using it. Look at what I'm doing. This is an Apple
00:00:56 - iPhone, right. It is SSH'ed into a CISCO firewall. Look
00:01:02 - I went into privilege mode enable. I typed in my password. I got into global
00:01:06 - config, from my phone.
00:01:08 - Isn't that awesome. I could fix a network issue from a red light
00:01:12 - on, on, on the road, or a green light for that matter. Why not?
00:01:16 - So, anyway, this, this thing is great. I'm telling you. There's, there's
00:01:19 - hundreds of programs for it, and you can get all kinds of, like,
00:01:23 - network sniffers for it.
00:01:25 - It's, it's amazing. I haven't figured out how to connect to consul table
00:01:28 - to it yet, but that's, that's, that's my latest cool thing. Okay.
00:01:32 - Let's talk about STP.
00:01:34 - So I've made some slight changes to this network diagram since the
00:01:38 - previous video. All I did for this configuring and testing spanning
00:01:43 - tree, is move the pc's back out of their vlan's. Now don't worry,
00:01:47 - that's a temporary thing. This is just gonna be the basic
00:01:50 - STP, before we get into all the enhancements, and to do that, everything
00:01:54 - is just put back into VLAN one. So you can see these two computers
00:01:58 - are out of their vlans. They're a sign. They're, they're a normal vlan 1
00:02:01 - IP addresses. They're able to ping each other again. These vlan's
00:02:04 - are still there. They're just, I guess you, we could put a
00:02:07 - little, not in use, because everything is currently joining
00:02:12 - vlan 1. Now, in order to set up redundancy, what I did was, connect
00:02:18 - a cross over cable between switch two and switch three, on
00:02:22 - fastEthernet0/24 on both of them. Now what that
00:02:26 - does, is create a redundant link, so if switch one goes down,
00:02:30 - switch two and switch three can still communicate, and the pc's can
00:02:33 - talk, they can still at least get across the WAN links, and so on.
00:02:35 - They'll just lose connectivity to whatever switch one was connected
00:02:38 - to, but when I introduce that link into the picture, we now
00:02:42 - have a loop in the network, so spanning tree needs to jump in
00:02:45 - and block one of these connections, but before we can determine
00:02:49 - which one it's gonna block, we have to Telnet in and do
00:02:53 - some show commands to find out who the root bridge is, so let's do
00:02:56 - that. I'm gonna take you to the,
00:03:01 - let's, let's just start on switch one, that's our core switch. So I'll
00:03:04 - take you to switch one and type in the show command. You can just
00:03:07 - type this in from any switch that's running spanning tree.
00:03:11 - Just type, show spanning tree. You can also type that from your Apple iPhone
00:03:15 - if you wanted to. Alright, I'll stop. You can see, I'm gonna stop the
00:03:19 - upper right there. You can see we have vlan 1 running right
00:03:22 - now, and it gives some information about spanning tree. It says,
00:03:25 - spanning tree is enabled protocol i triple e, meaning, its industry
00:03:28 - standard. Underneath here, you'll see it divided into two sections,
00:03:32 - Root ID and Bridge ID.
00:03:36 - This, right here, is the information about the root, meaning, the
00:03:41 - root switch currently has the priority 32769. It
00:03:47 - It currently has the mac address 008, you know, there's
00:03:50 - a mac address. It currently costs 19 to reach the root
00:03:53 - and I'm going out port FastEthernet0/11
00:03:59 - to get there. As a matter of fact, if you glance down under interfaces, you can see
00:04:03 - FastEthernet0/11 is designated as the root port. Okay.
00:04:08 - So all of this information right here, is information about
00:04:13 - the root bridge. This, is information about switch one, the switch
00:04:18 - that you're currently on. You can see the bridge ID is the
00:04:22 - mac address is this. The hello timing, and how often it is saying hello
00:04:26 - and, and checking the spanning tree topology. This is actually
00:04:29 - how often it's sending out BPD use, to say, hey, is there a loop in
00:04:33 - the network, once every two seconds, because to a switch, that's, that's
00:04:37 - not a problem. There's tons of bandwidth to use, so it's always
00:04:40 - checking to see if there's a new loop in the network. So this
00:04:43 - is the divide between the two. Now, you might remember,
00:04:46 - that I said the default priority on every switch is 32768.
00:04:50 - That was from the previous video when we talked about
00:04:53 - the concepts. Now CISCO switches run a special version of spanning
00:04:58 - tree we're going to talk about in the enhancements called per VLAN
00:05:01 - spanning tree. So what it actually does to enhance it, is that
00:05:06 - the vlan number. They call it a system ID extension to the
00:05:10 - priority, and so all the switches that are in vlan 1, have
00:05:13 - 32769 as their priority. If you were in vlan 10, you
00:05:17 - would have 32778, which would be the priority
00:05:22 - plus ten more. So it always adds the vlan number, but it's, it's
00:05:26 - the same thing. All the switches are tied on their priorities,
00:05:29 - so it's using the mac address to find out the, or to, to break
00:05:34 - the tie and, and determine the root bridge. So, while
00:05:38 - it's all fine and dandy that this has told us, hey, this is
00:05:41 - the root bridge, I mean, how do you know who has that mac address?
00:05:46 - Well it's time to trace some cables. You look at your network diagram and find
00:05:49 - find out on switch one, what does port 11 or FastEthernet0/11
00:05:53 - connect to.
00:05:56 - We jump back here, FastEthernet0/11 connects to switch two.
00:06:00 - So chances are, if you follow that link, you're gonna
00:06:05 - find the root bridge, and as a matter of fact, you can also notice,
00:06:08 - notice right here FastEthernet0/12 is blocked.
00:06:13 - So that gives us a big clue, choonk, choonk, that that link is
00:06:18 - disabled, because that is the least efficient connection. So
00:06:21 - the two active links right now, are these two, so you can kind of see
00:06:27 - and diagnose what spanning tree is doing. Now the problem is, the thirty
00:06:30 - our core. We want that to be our root. It's the bigger
00:06:33 - switch, but switch two became the root, just because it has
00:06:36 - an older mac address, an older manufacturing date, so that's the
00:06:40 - one that is currently active right now as the root bridge.
00:06:43 - So, well actually, let's jump on over to switch two, and just verify
00:06:48 - from there.
00:06:50 - I'm going to type in, show spanning tree
00:06:52 - Look at that. VLAN 1, Root ID, this is the root
00:06:56 - information, and it says right there, it's very blatant, this
00:07:01 - bridge is the root. You can look below and see that the mac
00:07:05 - address of the bridge ID, which is this switch, matches the
00:07:09 - mac address of the Root ID, because they're one and the same,
00:07:11 - same priority, same mac address. Notice every single port is considered
00:07:16 - designated, because the root bridge never blocks its ports.
00:07:20 - So as of right now,
00:07:23 - this switch, switch two, is our root, and that's why it makes
00:07:27 - sense that this link over here ended up being blocked. Now when
00:07:31 - comparing switch three and switch one, switch one must have
00:07:35 - an older mac address then switch three, because it blocked its
00:07:39 - side of the connection. Let me show you what I'm talking about. I'll jump over switch
00:07:42 - switch three and do a show spanning tree,
00:07:46 - and you can see, you know, from switch three's perspective, it's like, ay,
00:07:50 - everything's great. Root port, we've got designated ports all down here.
00:07:54 - This is what I was talking about in the previous video, that
00:07:56 - sometimes it's difficult to determine who's blocking their
00:07:59 - interface, because from switch three's end of the picture,
00:08:03 - it's saying, hey, I'm great, because only switch one has blocked
00:08:07 - its interface. Okay. So that's the idea. We verify that spanning
00:08:11 - tree is operating. It's not operating efficiency, because the wrong
00:08:15 - switch got elected as the root. So how do we change that?
00:08:19 - Let me show you the one major command of spanning tree. If
00:08:23 - you wanna run nothing but standard spanning tree, this is
00:08:26 - the only command that you'll need. However, in modern times,
00:08:30 - most people will apply some of the spanning tree enhancements, so
00:08:33 - we'll talk about in the next video, but this is it. We want
00:08:36 - switch one to be our root, right? So I'm gonna go up to switch one
00:08:42 - Let's do a show spanning tree there one more time, just to verify
00:08:47 - that as of right now, we have somebody else as the root, and
00:08:50 - we know that's, that is currently switch two, so I'm gonna go into global
00:08:54 - config mode and type in, spanning tree, followed by vlan 1, because
00:09:00 - we're modifying spanning tree for vlan 1. Everything in this network
00:09:03 - is running vlan 1 as of right now, so spanning tree vlan 1,
00:09:06 - I heard the question mark. The key that I'm looking for, well
00:09:10 - I can do it one of two ways. I can type in root space, and then
00:09:15 - choose my primary, primary or secondary. If I type in primary, it will
00:09:20 - lower my switch priority to the i triple e recommended value.
00:09:25 - The i triple e is the standards body who created spanning tree,
00:09:28 - They're gonna set it to a recommended value that they say
00:09:31 - should be the primary root. The secondary root could be a
00:09:35 - backup. For instance, if I had two core switches, or two major
00:09:39 - switches in my network that I wanted to be redundant for each
00:09:41 - other, I could set the secondary one as a backup for vlan 1.
00:09:47 - So, I'll show you the other method in just a second, but let's go
00:09:49 - back and do a show spanning tree and hit enter, and notice what happened
00:09:54 - The priority, not the mac address, the priority on my switch
00:09:59 - was decreased.
00:10:02 - It went down to 24577. Again there's
00:10:06 - that nice dart on the dart board, right, and just, that's
00:10:09 - a good recommendation. So that is below the 32769,
00:10:14 - that everything else is in the network. So immediately, this
00:10:17 - which now becomes the root. Notice, we have designated ports
00:10:21 - on every single one. All of them are forwarding, except for the one
00:10:25 - that was blocked. It's currently in a state of learning. If I
00:10:27 - hit the up arrow, again, now you can see it's forwarding. I'm actually gonna show
00:10:31 - you what all the states are in just a moment too.
00:10:34 - So, this is now the root, which means, the switch two over here,
00:10:40 - let's, let's adjust our diagram. This is now the root. Switch
00:10:44 - two must have been bumped down, so let's hop over to switch two, do a show
00:10:48 - spanning tree,
00:10:50 - and sure enough, you can see switch two is no longer the root.
00:10:54 - It's pointing to the root bridge, which has that better
00:10:57 - priority right there, which is currently switch one. Notice it
00:11:01 - It has one root port, two designated ports, so just guessing, well, very, very
00:11:07 - confident guessing, I can say that switch three must have
00:11:11 - blocked that interface, fastEthernet0/24
00:11:14 - on that side, because, since this one has all forwarding ports, there
00:11:18 - has to be a blocked port in the networks, so switch from switch
00:11:21 - must have been it, and you can see it right there, that
00:11:24 - fastEthernet0/24 is currently in a blocked
00:11:27 - state. So that is setting the, the root bridge to switch one,
00:11:32 - and that's what you want to do in any one of your networks.
00:11:35 - Spanning tree is so easy to forget about. You get involved in
00:11:39 - all kinds of, you know, complex configurations, and you're setting
00:11:42 - things up, and things aren't working, and you're working through the
00:11:45 - night on this brand new network, and you get everything set up and
00:11:48 - you're like, aah, I'm going home, and you forget all about spanning tree.
00:11:52 - It's one command, but if you forget it, the, the network will never
00:11:57 - really run as well as it could, because it's not gonna be
00:12:00 - set up using the most efficient root bridge possible, and they'll
00:12:04 - just be running slow, and sure, everybody's gonna get used
00:12:07 - to it, and they're gonna be like, well, I guess the network is just that slow,
00:12:11 - and, and life goes on, not realizing all along that you could have
00:12:15 - a much faster network if you would just have the root bridge set
00:12:18 - correctly.
00:12:19 - Now let me show you the other way to do it.
00:12:23 - That was using a handy keyword, which was the spanning tree vlan 1
00:12:28 - root primary. The other way that you can set the root bridge,
00:12:31 - is to type in spanning tree vlan 1, and set the priority.
00:12:35 - This will manually allow you to type in the priority of spanning
00:12:40 - tree, which this is the value,
00:12:43 - right here, that it came up for us with, when we went in and, and
00:12:49 - typed in the primary. So notice right here, it's saying you can
00:12:53 - use any value from zero, or zero is obviously the best, all the
00:12:57 - way up to 61440, but you have
00:13:00 - to use increments of 4096.
00:13:05 - I don't know. I know you're thinking why, why did they do it
00:13:09 - that way, just, because, because they did. So that is the, the
00:13:14 - range of the, the priorities that you can have, all in increments
00:13:18 - of 4096. So you could use 04096
00:13:21 - 8192, and, you know, just keep adding
00:13:25 - 4096 to find out all the different values.
00:13:28 - So if you wanted to, you could actually set it down to
00:13:31 - zero, to make sure that this one always becomes the root. By
00:13:35 - the way, that is a known hacking method. I should mention this.
00:13:40 - You can set up, you know, so let's say, let's say this guy in his
00:13:43 - cubicle's, a very angry person who wants to try and destroy his,
00:13:46 - destroy your network. He could plug a managed switch, meaning a high end
00:13:51 - switch into the network cubicle wall jack, and type in spanning
00:13:55 - tree vlan 1 priority zero, to where his switch becomes the
00:14:00 - root bridge, and then everybody points to that cubicle as the
00:14:03 - center of the network, and the whole thing just starts going
00:14:05 - really slow, because it's going through a cubicle wall jack to
00:14:09 - do most of its connectivity. So there are actually methods
00:14:13 - out there that you can put in. It's actually known as root guard,
00:14:16 - and, and BPDU Guard, and things like that. Those are security
00:14:20 - systems that you can turn on, that if somebody plugs in an unauthorized
00:14:23 - switch that tries to do that, it will shut their port right
00:14:27 - down. Ha, take that. Alright, so we've got the root bridge set up.
00:14:32 - Now I want to show you a fail over.
00:14:36 - Actually, let's jump back to the topology here. I'm gonna show you what I'm gonna do.
00:14:40 - As of right now, we know we've determined that switch one is
00:14:43 - the root bridge, because that's what we set it to. This port
00:14:47 - and this port are forwarding. This link is blocked. It's set as
00:14:50 - the backup connection, should any one of those links fail, that
00:14:53 - spanning tree is managing. So here's what I want to do. I want
00:14:57 - to initiate a ping, a continual ping from, let's see, I'm sitting
00:15:03 - on this pc right now, so I'll do a ping from this pc to this
00:15:07 - pc that's constantly going. Once that ping is going, I'm going
00:15:11 - to disable, we'll just say this link right here, shut it
00:15:15 - down, so that it, it is no longer operational. I wanna see how long
00:15:19 - spanning tree takes to detect that problem, and then activate
00:15:24 - this switch link. You're ready.
00:15:26 - to watch. Here we go.
00:15:28 - Let me bring up the command prompt first,
00:15:32 - and I'm gonna type in ping. Actually let me just verify which
00:15:36 - one I'm on, IP config.
00:15:39 - This is, let me just scroll go back up. The 192.168.1.50
00:15:43 - pc, which is the smiling pc down here, and shrink
00:15:47 - his window down,
00:15:49 - about that big, so we can have the config window at the same
00:15:51 - time. Now I'm gonna type in ping, 192.168.1.20 - t,
00:15:56 - which is a repetitive thing, meaning, it's
00:16:00 - gonna go nonstop. It's just gonna keep on pinging. Alright.
00:16:03 - So that's going where we're now actively pinging network station.
00:16:07 - Let me bring up, actually, slide it up here
00:16:11 - this, this configuration window, which is switch one. Now let's
00:16:15 - see if I can still see my network diagram.
00:16:18 - Switch one is, I'm going to shut down fastEthernet0/12,
00:16:21 - which will disable the active link that's
00:16:25 - currently working for spanning tree. I'm gonna keep these both
00:16:28 - in the window, right here, so let me go into interface that
00:16:32 - fastEthernet0/12 and do a shut down.
00:16:40 - Alright, it is shut down, the pings have now stopped. Notice, the,
00:16:44 - the connections timing out below. I'm going to, let me just hop
00:16:48 - on over to switch three. I'm gonna do a show spanning tree right now. Notice
00:16:54 - what, what, oops, notice what mode,
00:16:57 - I don't know if you caught that before. It was in, and look at this.
00:17:01 - We're down. The networks down right now. It was in listening
00:17:04 - mode on that back up port, then it went to learning mode, and
00:17:10 - look at that. Wham. We're now back on line. The, the switch is pinging.
00:17:15 - Now that was, I'm, I'm sure you know with my kind of banter, talking
00:17:20 - and so on, that was about 30 to 50 seconds of a network
00:17:25 - outage that occurred, just to allow spanning tree to fail over.
00:17:29 - Now that may sound like, okay, that's, no worries, life is good, but remember,
00:17:34 - our networks nowadays, are running connections like voice over
00:17:39 - IP. You have phones running on the network. You have active
00:17:43 - file transfers. You have replications. You have airline schedules.
00:17:46 - You have credit card transactions. You have stock quotes. All of this
00:17:50 - stuff is happening real-time, step step, step, step, step, flying
00:17:53 - across your network. If you have a network outage of two seconds,
00:17:57 - that's something more people are like, whoa, what just happened? Phone
00:18:00 - calls drop everywhere, stock quotes get kind of, you know, off
00:18:04 - in, in off shift. If you go for 30 to 50 seconds in, and let me,
00:18:08 - let me revise my excitedness here, 30 to 50 seconds
00:18:13 - in
00:18:14 - a production network, in a critical business network, you're gonna
00:18:19 - have a major crisis on your hands. What I just demonstrated,
00:18:23 - is, why spanning tree, as it stands right now, is not used very
00:18:28 - often in full enterprise networks. There's enhanced versions
00:18:32 - of it that we use. As a matter of fact, watch this. I'm going to go,
00:18:36 - let's see, back on to switch one,
00:18:39 - under fastEthernet0/12, and do a no shut down.
00:18:42 - Let's power that guy back on, yay, will fix everything, right. What
00:18:46 - it's going to do, as, as soon as all the links are detected and,
00:18:49 - and back on line. Notice, notice, you see my equal signs, they've stopped.
00:18:53 - The network has gone down again. I'm serious. I'm gonna do a show spanning tree,
00:18:59 - Look at this. FastEthernet0/12 has gone into it's
00:19:02 - nice little listening state there. Let's do a spanning tree. Now
00:19:05 - it's learning. Meanwhile, imagine people right now going ha, ha
00:19:09 - network down, phone calls dropping, customer dissatisfaction, airlines
00:19:12 - are out of wack, credit cards aren't being processed. See, I'm trying to,
00:19:16 - I'm trying to hype this up here.
00:19:18 - There's got, you know, there's, there's a major network, and finally, we're,
00:19:22 - we're still dying here. It looks like the port is forwarding, but
00:19:25 - something still hasn't come back online. This is actually
00:19:28 - known as a blocking timer. Eventually,
00:19:33 - give it 60 seconds, give it a minute and a half or so, eventually
00:19:37 - it will renegotiate, and the port will come back on line and
00:19:40 - go active. Spanning tree, the version that we just saw,
00:19:45 - was developed a long time ago. I mean, think when switches came
00:19:49 - out, that's when spanning tree came with it, because people wanted a
00:19:52 - redundant connection. So we're talking a, a technology, that a decade
00:19:56 - ago, it wasn't that big of a deal to have an outage of 30
00:19:59 - seconds. That's alright, but nowadays, we have to use enhanced
00:20:03 - versions. So there it is, basic spanning tree protocol, essentially
00:20:09 - a protocol that is necessary in our networks, but needs to
00:20:12 - be enhanced and upgraded, as we just saw. So, what we first off
00:20:16 - looked at, was enhancing our network diagram, by adding
00:20:20 - in a redundant link between the two switches, which spanning
00:20:24 - tree did its job. It identified it, and it blocked it. So we identified
00:20:29 - the current spanning tree configuration, which just the oldest
00:20:32 - switch that you have in your network, will be elected as the
00:20:34 - root bridge, and all the switches will find the best way to reach
00:20:38 - that root bridge, and then block all the redundant connections.
00:20:41 - So, what we need to do, is find the best switch in our network,
00:20:45 - even in the enhanced version. I, I don't mean to hype
00:20:48 - the enhanced version, like everything's better, everything's
00:20:50 - changed, although it is a lot better, but in the enhanced version,
00:20:54 - we still have to elect a root bridge. We still have to make
00:20:57 - sure that we have, you know, all the core technology of spanning tree
00:21:00 - even in, in the enhanced versions is the same. So we have to
00:21:04 - configure a root bridge and set that up as the core of our
00:21:06 - network, and all the switches will find the best way to the
00:21:10 - center and work from there.
00:21:13 - I hope this has been informative for you like to thank you for viewing.

Switch STP: Enhancements to STP

General Switching: Troubleshooting and Security Best Practices

Subnetting: Understanding VLSM

Routing Protocols: Distance Vector vs. Link State

Routing Protocols: OSPF Concepts

Routing Protocols: OSPF Configuration and Troubleshooting

Routing Protocols: EIGRP Concepts and Configuration

Access-Lists: The Rules of the ACL

Access-Lists: Configuring ACLs

Access-Lists: Configuring ACLs, Part 2

NAT: Understanding the Three Styles of NAT

NAT: Command-line NAT Configuration

WAN Connections: Concepts of VPN Technology

WAN Connections: Implementing PPP Authentication

WAN Connections: Understanding Frame Relay

WAN Connections: Configuring Frame Relay

IPv6: Understanding Basic Concepts and Addressing

IPv6: Configuring, Routing, and Interoperating

Certification: Some Last Words for Test Takers

Advanced TCP/IP: Working with Binary

Advanced TCP/IP: IP Subnetting, Part 1

Advanced TCP/IP: IP Subnetting, Part 2

Advanced TCP/IP: IP Subnetting, Part 3

Please help us improve by sharing your feedback on training courses and videos. For customer service questions, please contact our support team. The views expressed in comments reflect those of the author and not of CBT Nuggets. We reserve the right to remove comments that do not adhere to our community standards.

comments powered by Disqus

Course Features

Speed Control

Play videos at a faster or slower pace.

Bookmarks

Pick up where you left off watching a video.

Notes

Jot down information to refer back to at a later time.

Closed Captions

Follow what the trainers are saying with ease.

Offline Training

Our mobile apps offer the ability to download videos and train anytime, anywhere offline.

Accountability Coaching

Develop and maintain a study plan with assistance from coaches.
Jeremy Cioara

Jeremy Cioara

CBT Nuggets Trainer

Certifications:
Cisco CCNA, CCDA, CCNA Security, CCNA Voice, CCNP, CCSP, CCVP, CCDP, CCIE R&S; Amazon Web Services CSA; Microsoft MCP, MCSE, Novell CNA, CNE; CompTIA A+, Network+, iNet+

Area Of Expertise:
Cisco network administration and development. Author or coauthor of numerous books, including: CCNA Voice 640-461 Official Cert Guide; CCNA Voice Official Exam Certification Guide (640-460 IIUC); CCENT Exam Prep (Exam 640-822); CCNA Exam Cram (Exam 640-802) 3rd Edition; and CCNA Voice 640-461 Official Cert Guide.


Stay Connected

Get the latest updates on the subjects you choose.


  © 2014 CBT Nuggets. All rights reserved. Licensing Agreement | Billing Agreement | Privacy Policy | RSS