Free CCNA | CDP & LLDP | Day 36 | CCNA 200-301 Complete Course

Welcome to Jeremy’s IT Lab. This is a free, complete course for the CCNA. If you like these videos, please subscribe to follow along with the series.

Also, please like and leave a comment, and share the video to help spread this free series of videos. Thanks for your help. In this video we will cover two Layer 2 discovery protocols, CDP and LLDP.

You might not have heard of a Layer 2 discovery protocol before, but I’ll explain what they are in this video. CDP and LLDP are exam topic 2. 3, which says you must be able to configure and verify Layer 2 discovery protocols CDP and LLDP.

CDP and LLDP are important topics for the CCNA, but there’s not as much information to absorb compared to topics like ACLs, IPv6, and OSPF. So, hopefully this video will be a little easier to get through. Here’s what we’ll cover in this video.

First I’ll give a brief overview of Layer 2 discovery protocols. Then I’ll cover Cisco Discovery Protocol, CDP. Finally I’ll cover Link Layer Discovery Protocol, LLDP.

CDP and LLDP are very similar in terms of function and configuration, but there are some key differences. Watch until the end of today’s video for a bonus practice question from Boson Software’s ExSim for CCNA. ExSim simulates the style and difficulty of the real CCNA exam better than any other practice exams, and I highly recommend ExSim to anyone preparing for the CCNA.

Let’s get started with a brief intro to Layer 2 discovery protocols. Layer 2 discovery protocols such as CDP and LLDP share information with, and discover information about, neighboring (connected) devices. They are called ‘Layer 2’ discovery protocols because the protocols themselves operate at Layer 2, they don’t use IP addresses.

We’ll look at some Wireshark captures later, and you’ll see that there are no IP packets inside of the frames sent by CDP and LLDP. Although they are Layer 2 discovery protocols, they can be used to share layer 3 information such as IP addresses too. The shared information includes host name, IP address, device type, etc.

CDP is a Cisco proprietary protocol, developed by Cisco for Cisco devices. LLDP is an industry standard protocol, IEEE 802. 1AB.

So, if your network uses only Cisco devices CDP is fine. However if there is a mix of vendors, for example Cisco routers, Juniper switches, and Palo Alto firewalls, you will have to use LLDP if you want to use a Layer 2 discovery protocol in your network. However, because these protocols share information about the devices in the network, they can be considered a security risk and are often not used.

It’s up to the network engineer or admin to decide if they want to use them in the network or not. At my workplace, for example, we always disable these protocols, but I’m sure many networks make use of them. To demonstrate how these protocols work, here are two devices, R1 and SW1, directly connected.

R1 will periodically send frames to SW1, telling it information like R1’s hostname, device type, interface ID, IP address, etc. SW1 will do the same, periodically sending frames to R1. Note that SW1 doesn’t include an IP address in the information it sends to R1, because it’s a switch.

Its interface doesn’t have an IP address. So let’s move on to talk about CDP specifically. To repeat, CDP is a Cisco proprietary protocol.

It is enabled on Cisco devices by default. For example Cisco routers, Cisco switches, Cisco firewalls, Cisco IP phones, etc. All of these devices have CDP enabled by default.

CDP messages are periodically sent to multicast MAC address 0100 0CCC CCCC. Remember that MAC address, it will be in the flashcards. I know the MAC addresses used by different protocols such as CDP, STP, PVST, HSRP, VRRP, etc are difficult to memorize.

The Anki flashcards are very helpful for this. You can add a specific tag to these MAC address cards, and use the tag to review those specific cards whenever you want. This will help you remember all of these MAC addresses, and which is used for which protocol.

Anyway, if you want to learn Anki functions like that do a Google search, let’s continue with CDP. Because the messages use a multicast MAC address you might think the message is forwarded to multiple devices, but it isn’t. When a device receives a CDP message, it processes and discards the message.

It does not forward it to other devices. So, only directly connected neighbors can become CDP neighbors. By default, CDP messages are sent once every 60 seconds, out of all interfaces which are in an up state.

These are the messages that contain the information like host name, IP address, etc, that I summarized in the previous When a device receives these CDP messages from a neighboring device, it adds an entry for the device in its CDP neighbor table. If a neighbor is disconnected, there is a default CDP holdtime of 180 seconds. So, if a message isn’t received from a neighbor for 180 seconds, the neighbor is removed from the CDP neighbor table.

This makes sure the CDP neighbor table doesn’t have entries from old neighbors which used to be connected, but no longer are. CDP version 2 messages are sent by default. There are two versions of CDP, version 1 and version 2, but version 2 is used by default.

CDP version 1 is very old so you’ll probably never need to use it. You don’t need to know the differences between version 1 and version 2, but basically version 2 provides a few more advanced features like the ability to identify native VLAN mismatches. Okay let’s get right into the CLI to see exactly what information is shared by CDP.

To demonstrate CDP, as well as LLDP later, I’ll use this network. Two routers and two multilayer switches, although I’m not using any Layer 3 functions on the switches. Before looking at the CDP neighbor table, here are a few other basic CDP show commands.

SHOW CDP tells us the CDP timer, 60 seconds by default, the CDP holdtime, 180 seconds by default, and it also shows which version of CDP is being used, version 2 by default. Note that if CDP isn’t enabled on the device, you’ll get a message like this when you try to use the SHOW CDP command: CDP is not enabled. Okay, next I used the command SHOW CDP TRAFFIC.

This command tells us how many CDP packets, how many CDP advertisements, the device has sent and received. At the time that I used this command, R1 had sent 105 CDP messages and received 112 CDP messages, and all of those messages were CDP version 2 messages. Finally, you can use the SHOW CDP INTERFACE command, which gives some basic information about each interface.

You can also specify a certain interface when entering the command, but if you just enter SHOW CDP INTERFACE you’ll get information about all interfaces. Here you can see the info for G0/0. You can see the same CDP message timer and holdtime as above, but what does ‘encapsulation ARPA’ mean?

ARPA is actually a type of Ethernet encapsulation. I haven’t talked about the different types of Ethernet in this course, I’m pretty sure that’s beyond the scope of the CCNA, but I just wanted to point that out because I’m sure some of you would be wondering about it. This type of Ethernet is also known as Ethernet 2, so if you want to learn more try a Google search for Ethernet 2.

Okay, finally down here you can see a basic summary of how many interfaces are CDP-enabled, and how many interfaces are in an up state and a down state. So, remember these three commands, SHOW CDP, SHOW CDP TRAFFIC, and SHOW CDP INTERFACE. Finally let’s look at the CDP neighbor table.

Here it is, on R1 I used the command SHOW CDP NEIGHBORS to view it. Let’s look at what you can learn from this command. First, the ‘device ID’ column lists the host name of each of R1’s CDP neighbors.

So, R1 has received CDP messages from SW1 and R2. Next is the ‘local interface’ column. This states the interface on the local device, on R1.

So, if we didn’t have a proper network diagram and wanted to know which devices are connected to which interface on R1, we can use this command. SW1 is connected to R1’s G0/0 interface, and R2 is connected to R1’s G0/1 interface, as shown in the network diagram below. Next is the holdtime column.

This will reset to 180 each time R1 receives a CDP message from the neighbor. With the default timers, it should count down to 120, then R1 will receive a CDP message and reset it to 180, and that cycle will repeat. If this timer reaches 0, the neighbor will be removed from the CDP neighbor table.

Next is the ‘capability’ column. This helps you identify what kind of device you are connected to. For example, SW1 has the letters R, S, and I.

What do these codes mean? You can check up here. First off, let me point out that I means IGMP.

This is related to multicast and is beyond the CCNA, don’t worry about it for now. Then, R means router and S means switch. Switch is obvious, SW1 is a switch, but why router?

It’s because this is a multilayer switch, so it has routing capabilities. That’s why it’s listed as both a router and a switch. Now, how about R2?

It has R and B in its capability column. Once again, R stands for router, which is expected because R2 is a router. And B means ‘source route bridge’.

This is another thing that isn’t necessary for the CCNA, so don’t worry about memorizing it. So, I recommend just remembering R for router and S for switch. Next is the ‘platform’ column.

This displays the model of the neighboring device. As you know, Cisco has various models of routers, switches, firewalls, etc, and the model will be displayed here. However, for these lessons I use virtual devices running in GNS3, and as you can see nothing is displayed here, since they aren’t physical devices.

So, let’s refer to Packet Tracer which actually does display information here. For example, in the Packet Tracer network I made, R1 was connected to a C2900 series router, R2, and a catalyst 2960 series switch, SW1. Okay, last column is ‘port ID’.

This tells you the port ID on the neighboring device. So, R1 is connected to SW1’s G0/0 interface and R2’s G0/0 interface. Make sure you know the difference between the ‘local interface’ field, the interface on this device, and the ‘port ID’ field, the interface on the neighboring device.

Okay, those are all of the fields of SHOW CDP NEIGHBORS, but there is more information you can learn via CDP. To view that additional information you can use this command: SHOW CDP NEIGHBORS DETAIL. As you can see, more information is displayed for each neighbor.

For example, here’s SW1’s entry. Some of the information you can see here that you couldn’t see with the regular SHOW CDP NEIGHBORS command is the software version, the version of IOS, running on the neighbor device. Because SW1 is a switch, you can also see VTP information here.

This is something CDP can do but LLDP can’t. VTP is a Cisco proprietary protocol, so only Cisco’s CDP can share information about it. You can also see the native VLAN of SW1’s interface, currently it’s the default of 1.

The duplex setting of SW1’s interface is displayed, also. So, with these last two fields CDP helps identify any mismatches of native VLAN or interface duplex. Actually, if a mismatch is found CDP will display messages on the device to let you know.

Next here’s R2’s entry. I just wanted to point out that you can see R2’s IP address here, 10. 0.

0. 2. SW1 doesn’t have any IP addresses, so none were displayed above, but the SHOW CDP NEIGHBORS DETAIL command lets you view the neighbor’s IP address.

Now, if the device has a lot of CDP neighbors the output of this command can get quite long. However, there is another command which lets you view this detailed information for just a single neighbor. That is this command, SHOW CDP ENTRY, followed by the neighbor’s host name, I used R2 in this case.

The output here is exactly the same as in SHOW CDP NEIGHBORS DETAIL, but it only shows the specified neighbor. Here’s a brief summary of each of the commands I just showed you. I won’t go over them individually, feel free to pause the video here if you want to review them.

Because CDP is enabled by default, if you want to use CDP in your network you don’t have to do any configuration, you can just use these SHOW commands. But now let’s take a look at some basic CDP configurations. As I just said, CDP is globally enabled by default, Cisco devices have CDP activated by default.

Each interface also has CDP enabled by default. If you want to enable or disable CDP globally, use the CDP RUN command from global config mode. Use CDP RUN to enable it, which is default, or NO CDP RUN to disable it.

To enable CDP on an interface, which is the default state, use CDP ENABLE, and use NO in front of the command to disable it. These commands are done from interface config mode. You can configure the CDP timer, how often CDP messages are sent, with the CDP TIMER command from global config mode.

You can also configure the holdtime with CDP HOLDTIME. And you can enable CDP version 2, which is the default state, with CDP ADVERTISE-V2, or use NO in front of the command to disable it and use version 1. You’ll probably never use that last command, but I included it anyway.

So, these are the CDP configuration commands you should know for the CCNA. CDP RUN, CDP ENABLE, CDP TIMER, CDP HOLDTIME, and CDP ADVERTISE-V2. Finally let’s move on to LLDP, Link Layer Discovery Protocol.

LLDP is an industry standard protocol, so many different vendors implement it on their devices. CDP was the original, and LLDP was later invented to have an industry standard version. It is usually disabled on Cisco devices by default, so it must be manually enabled.

A device can run CDP and LLDP at the same time, so you don’t have to choose between them, although usually you’ll just use one. Here’s another MAC address to remember. LLDP messages are periodically sent to multicast MAC address 0180 C200 000E.

Again, use the flashcards to remember that one. This is the same as for CDP. When a device receives an LLDP message, it processes and discards the message.

It does not forward it to other devices. So, only directly connected devices can become LLDP neighbors. By default, LLDP messages are sent once every 30 seconds, this is half the time of CDP’s default 60 seconds.

LLDP’s default holdtime is 120 seconds. LLDP also has an additional timer called the ‘reinitialization delay’. I don’t think you need to know this for the CCNA, but here’s a very brief explanation.

If LLDP is enabled, either globally or on a specific interface, this timer will delay the actual initialization of LLDP, and the timer is 2 seconds by default. I believe the purpose of this timer is to help in cases of ‘flapping’, when LLDP is rapidly enabled or disabled for some reason. So, the device won’t send LLDP messages out of its interfaces immediately when LLDP is enabled, it will wait for the initialization timer to expire.

As I said, you probably don’t have to know that for the CCNA, but you’ll see that timer in the output of the commands I’m going to show you, so I wanted to give a brief explanation. Because LLDP is disabled by default, before checking out the SHOW commands let’s see the configuration commands you should know for LLDP. To review, LLDP is usually globally disabled by default, and it’s also disabled on each interface by default.

So, to enable LLDP you need to enable it globally and then enable it on each interface. You’ll see that the interface configuration is a little different than CDP. To enable it globally use LLDP RUN.

This is the same as CDP, just replace the word CDP with LLDP. If you want to disable it again after, use NO in front of the command. Now the interface configurations.

To enable LLDP transmissions, tx, on an interface, use LLDP TRANSMIT on the interface. This causes the interface to start sending LLDP messages. However, it won’t receive LLDP messages, it will simply discard them.

To enable LLDP in the receive direction, rx, use the LLDP RECEIVE command on the interface. So, CDP had only one command, CDP ENABLE which enables the interface to both send and receive CDP messages. In LLDP, you need to use two separate commands.

But still, the configuration is quite simple. Now let’s see how to configure each LLDP timer. The timer used to send messages is configured with LLDP TIMER, then the timer in seconds.

The LLDP holdtime is configured with LLDP HOLDTIME, then the holdtime in seconds. Finally, you can configure the LLDP reinitialization timer, which I briefly mentioned earlier, with LLDP REINIT, then the timer in seconds. So, these commands are all fairly similar to the CDP commands, the biggest difference is the interface configuration.

Make sure you enable both TRANSMIT and RECEIVE, unless for some reason you want the interface to only be able to send or receive, not send and receive, LLDP messages. So, I’ve enabled LLDP on all of these devices with the command LLDP RUN from global config mode, and LLDP TRANSMIT and RECEIVE on all interfaces. They are now running both CDP and LLDP.

Usually LLDP would be used in a multi-vendor network, not just Cisco, but this setup is good enough for our purposes, to demonstrate how LLDP works on Cisco devices. So, let’s check out some LLDP show commands, the LLDP versions of the ones I used for CDP. First, SHOW LLDP gives the same information as SHOW CDP does for CDP.

It shows that LLDP is enabled, and displays each of the LLDP timers, which are currently at the default settings of 30, 120, and 2 seconds. Then SHOW LLDP TRAFFIC, similar to SHOW CDP TRAFFIC, shows statistics about how many LLDP frames were sent and received. In this case I used the command quickly after enabling LLDP, only 4 frames have been sent and only 3 have been received by R1.

Then I used SHOW LLDP INTERFACE. This shows whether TRANSMIT and RECEIVE are enabled or disabled on each interface, as well as the current Tx and Rx state. For example, for G0/0 both Tx and Rx are enabled.

The Tx state is IDLE, it’s waiting before it sends the next LLDP frame to SW1. And the Rx state is WAIT FOR FRAME. It’s waiting to receive the next LLDP frame from SW1.

Okay, so those commands are very similar to their CDP equivalents, although there are some differences in the output. Now let’s check out R1’s LLDP neighbor table. Here’s R1’s LLDP neighbor table, the command is SHOW LLDP NEIGHBORS.

First up, the device ID, the host name, of each neighbor is displayed. Then the local interface. Just like in SHOW CDP NEIGHBORS, this is the interface of the local device, R1 in this case.

Then the hold time. This is a little different than in SHOW CDP NEIGHBORS. In SHOW CDP NEIGHBORS, you could watch the timer count down from 180, and then reset to 180 when a CDP message is received.

However SHOW LLDP NEIGHBORS simply displays the holdtime that is configured on this device, 120 seconds. It won’t count down as R1 waits for an LLDP message from each neighbor. Then the capability column.

The output here is a little odd. SW1 shows nothing, and R2 shows R. R means router, which you would expect from R2, because it’s a router.

However, why doesn’t the switch capability display for SW1? Actually, there is no ‘SWITCH’ capability code. Instead, LLDP uses B for Bridge.

Remember I told you, in the spanning tree lessons, that sometimes the word ‘bridge’ is used instead of switch? Well here’s another case of that. However, B isn’t displaying for SW1.

I think this is just because I’m running these virtual devices in GNS3, it isn’t detecting that SW1 is an active switch, but in the next when we look at SHOW LLDP NEIGHBORS DETAIL you will see this bridge code for SW1. Okay, and just like in SHOW CDP NEIGHBORS, the last column is the port ID, the interface ID of the neighboring device. R1 is connected to SW1’s G0/0 interface and R2’s G0/0 interface.

So, this command is very similar to SHOW CDP NEIGHBORS, but there are a few differences. Okay, here’s SHOW LLDP NEIGHBORS DETAIL on R1. The output is too long to show on one screen, so R2’s entry is cut off a little at the bottom.

Let’s check out SW1’s entry. It gives us additional information like the operating system version running on SW1. We can also see the ‘time remaining’.

This is the holdtime, if you want to actually see it counting down for each neighbor you have to use the DETAIL version of the command. And here is the main thing I want to show you. CDP had one field for the device’s capabilities, but LLDP has two when you use SHOW LLDP NEIGHBORS DETAIL.

‘System capabilities’ and ‘enabled capabilities’. If you look at system capabilities, you can see B and R. B is for bridge, meaning switch.

And R is for Router. So, this is what you would expect, because SW1 is a multilayer switch. It has the functions of both a router and a switch.

However, in this case the ‘enabled capabilities’ field simply displays ‘not advertised’, so none of SW1’s capabilities are enabled. If we use the IP ROUTING command on SW1, SW1’s router functionality will be enabled and the ‘R’ from ‘system capabilities’ will be copied to ‘enabled capabilities’. However, I think the reason ‘B’ isn’t displayed next to ‘enabled capabilities’ is simply because SW1 is a virtual device running in GNS3, it’s not recognized as an active switch.

You don’t have to worry about these details, but I just wanted to explain why it’s displaying like this. Note that this command doesn’t display VTP information like SHOW CDP NEIGHBORS DETAIL did. VTP is a Cisco-proprietary protocol, so only Cisco’s proprietary CDP can display info about VTP.

The industry-standard LLDP can’t. Okay, just like for CDP there is a command you can use to view the exact same output as SHOW LLDP NEIGHBORS DETAIL, but for a single neighbor instead of all neighbors. That command is SHOW LLDP ENTRY, followed by the neighbor’s host name.

By the way, before using this command I enabled IP ROUTING on SW1, and now you can see ‘R’, for Router, is displayed next to ‘enabled capabilities’ for SW1. Here’s the same SHOW command summary as before, but this time for LLDP. The commands are the same, just replace the word CDP with LLDP.

The output for these commands is similar to the output for CDP, but as you saw already there are a few differences. Pause the video if you want to review these commands, but let’s move on. Let’s briefly look at a couple Wireshark captures, one for CDP and one for LLDP.

First, this is a CDP message sent from R1 to SW1. Notice the CDP destination MAC address, 0100. 0CCC.

CCCC. But notice that Wireshark describes this destination MAC as CDP/VTP/DTP/PagP/UDLD. That’s because this same multicast MAC address is actually used for multiple protocols, not just CDP.

Now, here’s the actual CDP information. You can see here that CDP version 2 is being used. The TTL, time to live, is actually the CDP holdtime.

Here are some other fields such as the device ID, this is being sent from R1, the version, platform, addresses, and port ID. I could expand each of these fields in Wireshark to view more details, but then the capture wouldn’t fit on one screen,. So I just expanded the capabilities field, and you can see there is a ‘1’ for ‘Router’ and ‘Source Route Bridge’, those are the capabilities of R1.

Finally, notice that there is no IP packet inside of this Ethernet frame. These Layer 2 discovery protocols don’t use IP addresses, only MAC addresses. And here’s an LLDP frame capture, this time a message that SW1 sent to R1.

First up, here’s the destination MAC address I showed you earlier, 0180. C200. 000E.

And here’s the actual LLDP information. The time to live, TTL, is the LLDP holdtime of 120 seconds, and you can see the system name, the host name, of the device which sent this message, SW1. Here’s the LLDP capabilities field.

Just like we saw before, SW1’s capabilities are Bridge and Router, but its only enabled capability is router. Okay, you don’t have to look into these captures in too much detail, I just wanted to show you some real examples of CDP and LLDP messages. Before moving on to the quiz let’s review what we studied in today’s video.

First I gave a brief intro to Layer 2 discovery protocols and their purpose. Basically, they enable directly connected neighbors to share various information with each other such as host name, device type, IP address, software version, etc. They can be very useful and convenient, but remember that they can also be considered a security risk because of the information they share with connected devices.

So, many network admins choose to disable them in their networks. Then I introduced CDP, Cisco’s Layer 2 discovery protocol. After that I introduced LLDP, which was developed after CDP as an industry standard alternative.

LLDP is supported by many vendors, so if your network uses a mix of Cisco, Juniper, Palo Alto, Fortinet, whatever, you’ll have to use LLDP, not CDP. Make sure to watch until the end of the quiz for a bonus question from Boson Software’s ExSim for CCNA, the best practice exams for the CCNA, and the practice exams I used to prepare for my CCNA exam. Okay, let’s move on to the quiz.

Here’s question 1. Which of the following commands show the configured CDP timers? Select two.

A, SHOW CDP. B, SHOW CDP TRAFFIC. C, SHOW CDP INTERFACE.

Or D, SHOW CDP NEIGHBORS. Pause the video to think about your answers, select two. The answers are A and C.

Both of these commands show the configured CDP message time and holdtime. D, SHOW CDP NEIGHBORS does show the current holdtime counting down as the device waits for a CDP message from its neighbor, but it doesn’t show the actual configured holdtime. It also doesn’t display the CDP message timer, so it’s not one of the best answers.

Okay, let’s go to question 2. Which of the following commands represent the default CDP state? Select two.

A, NO CDP RUN. B, CDP HOLDTIME 120. C, CDP ENABLE, from interface config mode.

Or D, CDP TIMER 60. Pause the video to think about your answers, select two. The answers are C and D.

CDP ENABLE enables CDP on an interface, which is the default state. D sets the CDP message timer to 60 seconds, which is the default. A, NO CDP RUN, disables CDP on the router, and that is not the default state, CDP is enabled by default.

B, CDP HOLDTIME 120 sets the hold time to 120 seconds, which is not the default. The default CDP holdtime is 180 seconds. So, A and B are incorrect.

Let’s go to question 3. You issue the show lldp entry SW1 command on R1. R1’s neighbor SW1 is a multilayer switch.

What do you expect to see in the ‘system capabilities’ field of the output? Here are the options. Pause the video to think about your answer.

The answer is B, System Capabilities: B,R. B is for bridge, which is another word for switch. R is for router.

Because SW1 is a multilayer switch, it has the functionalities of both a switch and a router. S, as shown in options C and D, means switch in CDP, but it does not mean switch in LLDP. Okay, let’s go to question 4.

Which of the following statements about LLDP are true? Select two. Here are the options.

Pause the video now, read each option, and select the two correct choices. Okay, the correct answers are B and F. When configuring LLDP, unlike CDP, you must enable TRANSMIT, Tx, and RECEIVE, Rx, separately on each interface.

So, B is correct. And LLDP can be used to learn the OS version of a neighboring device, so F is also correct. The other options are incorrect statements about LLDP.

LLDP is an industry standard protocol, so A is incorrect. Its default message timer is 30 seconds, so C is incorrect. It can’t be used to learn the OSPF settings of a neighbor, so D is incorrect.

And it can’t be used to learn the VTP settings of a neighbor, although CDP can be used to do that, so E is incorrect. Okay, let’s go to question 5. Which interface on R2 is SW2 connected to?

Is it G0/0, G0/1, G0/2, or G0/3? Pause the video to examine R2’s CDP neighbor table and select the correct answer. The correct answer is G0/1.

It is shown here, in the local interface column of the output. This shows the interface on R2 that SW2 is connected to. Okay, that’s all for the quiz.

Now let’s try a bonus question from Boson Software’s ExSim for CCNA. Okay here's today's Boson ExSim practice question. You issue the following command on your router.

SHOW CDP NEIGHBORS. Which of the following information will be displayed? Select 4 choices.

A, the IP address of the neighboring device. B, the interface on the neighboring device that is connected to RouterA. C, The device ID of the neighboring device.

D, the software version running on the neighboring device. E, the interface on RouterA that is connected to the neighboring device. Or F, the capabilities and product number of the neighboring device.

Okay, pause the video now to think about your answer. Select 4 choices. Okay, let's check.

Let's go through one by one and see which answers are correct. So A, the IP address of the neighboring device. I think that is not displayed by SHOW CDP NEIGHBORS.

To view that you have to use SHOW CDP NEIGHBORS DETAIL, so A is not correct. B, the interface on the neighboring device that is connected to RouterA. That is correct.

You can see that with SHOW CDP NEIGHBORS. C, the device ID of the neighboring device. You can also see that, that is the host name of the neighboring device.

D, the software version running on the neighboring device. I think you cannot see that in SHOW CDP NEIGHBORS. Once again, you have to use SHOW CDP NEIGHBORS DETAIL to view the software version, the operating system version of the neighboring device.

Okay, E, the interface on RouterA that is connected to the neighboring device. You can see that with SHOW CDP NEIGHBORS. And how about F?

The capabilities, which is like router, switch, etc, and product number, this is the model of the device, of the neighboring device. And yes you can. So I think these are the four choices.

You cannot see the IP address of the neighboring device or the software version of the neighboring device. To view those two you have to use SHOW CDP NEIGHBORS DETAIL. Okay, so to check my answer I will click down here, show answer.

And that is correct. So, here is Boson's explanation. I'll scroll through it.

You can pause the video to read their explanation, and I really recommend you do. Boson gives great explanations, not just why each correct answer is correct, but also why each incorrect answer is incorrect. So they are a great resource to improve your understanding.

Okay, and at the bottom there are a few references to the official cert guide by Wendell Odom. This is a great book for studying for the CCNA. And also some Cisco documentation about CDP which is free to read online.

Okay, so that's Boson ExSim for the CCNA. If you want to get ExSim, please follow the link in the video description. These are by far the best practice exams for the CCNA.

Once again, follow that link in the video description. There are supplementary materials for this video. There is a flashcard deck to use with the software ‘Anki’.

There will also be a packet tracer practice lab so you can get some hands-on practice. That will be in the next video. Sign up for my mailing list via the link in the description, and I’ll send you all of the flashcards and packet tracer lab files for the course.

Before finishing today’s video I want to thank my JCNP-level channel members. To join, please click the ‘Join’ button under the video. Thank you to Magrathea, Samil, Aaron, Junhong, Njabulo, Benjamin, Tshepiso, Justin, Prakaash, Nasir, Erlison, Apogee, Marko, Daming, Joshua, Jhilmar, Ed, Value, John, Funnydart, Velvijaykum, C Mohd, Mark, Yousif, Boson Software, Devin, Lito, Yonatan, and Vance.

Sorry if I pronounced your name incorrectly, but thank you so much for your support. This is the list of JCNP-level members at the time of recording by the way, December 13th 2020. If you signed up recently and your name isn’t on here don’t worry, you’ll be in future videos.

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