Config Lab: IPv4 Addresses 5

 In 200-301 V1 Ch16: Router Addresses and Routes, 200-301 V1 Part 5: IPv4 Routing, 200-301 V1 Parts, Config Lab, Config Lab CCNA Vol 1 Part 4, Config Lab CCNA Vol 1 Part 5, Hands-on

More practice practice practice! This time, you get some basic IP addressing requirements. Your job: calculate the IP addresses to be used by routers and hosts, and create the router configuration for in the interfaces in the network diagram. No guile, no tricks, just a chance to exercise.

All about Config Labs

The blog has a series of lab exercises called “Config Labs.” Each lab presents a topology with the relevant initial configuration for each device. The lab also lists new requirements, after which you should create the additional configuration to meet those requirements. You can do the lab on paper, in a text editor, or use software tools like Cisco Packet Tracer or Cisco Modeling Labs.

Once you have created your answer, you can click various tabs at the bottom of this post to see the lab answers, comments about the lab, and other helpful information.

The Lab Exercise


This lab asks you to configure all the router IP addresses for the design shown in Figure 1, given a set of requirements. At this point, do not configure static routes or a routing protocol; just configure the IP addresses per the following specific instructions:

  1. Use the subnets as listed in Figure 1.
  2. Routers must use the highest IP address(es) in each subnet.
  3. If more than one router exists in a subnet, the router with the higher number in the hostname gets the higher IPv4 address. EG, R3 would have a higher IPv4 address than R2.
  4. Hosts should use the lowest IPv4 address in the subnet, with the same tiebreaker concept as stated in #2.

Figure 1: Router Triangle with IPv4 Subnets

Table 1 shows a way to organize the addresses for reference.

Location Address/Mask
R1 G0/0
R1 G0/2/0
R1 G0/3/0
R2 G0/0
R2 G0/1/0
R2 G0/3/0
R3 G0/0
R3 G0/1/0
R3 G0/2/0

Table 1: IPv4 Addresses

Answer Options - Click Tabs to Reveal

You can learn a lot and strengthen real learning of the topics by creating the configuration – even without a router or switch CLI. In fact, these labs were originally built to be used solely as a paper exercise!

To answer, just think about the lab. Refer to your primary learning material for CCNA, your notes, and create the configuration on paper or in a text editor. Then check your answer versus the answer post, which is linked at the bottom of the lab, just above the comments section.

You can also implement the lab using the Cisco Packet Tracer network simulator. With this option, you use Cisco’s free Packet Tracer simulator. You open a file that begins with the initial configuration already loaded. Then you implement your configuration and test to determine if it met the requirements of the lab.

(Use this link for more information about Cisco Packet Tracer.)

Use this workflow to do the labs in Cisco Packet Tracer:

  1. Download the .pkt file linked below.
  2. Open the .pkt file, creating a working lab with the same topology and interfaces as the lab exercise.
  3. Add your planned configuration to the lab.
  4. Test the configuration using some of the suggestions below.

Download this lab’s Packet Tracer File

You can also implement the lab using Cisco Modeling Labs – Personal (CML-P). CML-P (or simply CML) replaced Cisco Virtual Internet Routing Lab (VIRL) software in 2020, in effect serving as VIRL Version 2.

If you prefer to use CML, use a similar workflow as you would use if using Cisco Packet Tracer, as follows:

  1. Download the CML file (filetype .yaml) linked below.
  2. Import the lab’s CML file into CML and then start the lab.
  3. Compare the lab topology and interface IDs to this lab, as they may differ (more detail below).
  4. Add your planned configuration to the lab.
  5. Test the configuration using some of the suggestions below.

Download this lab’s CML file!


Network Device Info:

This table lists the interfaces used in the lab exercise documentation that differ from those used in the sample CML file.

Device Lab Port  CML Port
R1 G0/1/0 G0/1
R1 G0/2/0 G0/2
R2 G0/1/0 G0/1
R2 G0/3/0 G0/3
R3 G0/1/0 G0/1
R3 G0/3/0 G0/3

Lab Answers Below: Spoiler Alert

Lab Answers: Configuration (Click Tab to Reveal)


Your first task was to calculate the IP addresses to use, based on requirements. For reference, Table 1 lists the results. Note that all subnets use a /26 ( mask in this particular exercise.

Location IP/mask
R1 G0/0 /26
R1 G0/2/0 /26
R1 G0/3/0 /26
R2 G0/0 /26
R2 G0/1/0 /26
R2 G0/3/0 /26
R3 G0/0 /26
R3 G0/1/0 /26
R3 G0/2/0 /26

Table 1: IPv4 Addresses

Also, note that PC3 was pre-configured with an incorrect IP address ( instead of the lowest IP address in that subnet ( To complete the work on the PCs, use the packet tracer GUI to re-configure the address. (The default gateway should already be configured to the correct address.)

To create the configuration, all you have to do is add the ip address command to each interface in configuration mode. Easy once you’d done it a few times; here are the answers to be complete.

interface GigabitEthernet0/0
 ip address
interface GigabitEthernet0/2/0
 ip address
interface GigabitEthernet0/3/0
 ip address

Example 1: R1 IPv4 Address Configuration


interface GigabitEthernet0/0
 ip address
interface GigabitEthernet0/1/0
 ip address
interface GigabitEthernet0/3/0
 ip address

Example 2: R2 IPv4 Address Configuration


interface GigabitEthernet0/0
 ip address
interface GigabitEthernet0/1/0
 ip address
interface GigabitEthernet0/2/0
 ip address

Example 3: R3 IPv4 Address Configuration

Commentary, Issues, and Verification Tips (Click Tabs to Reveal)

This lab focuses on the math to determine the numerically highest IP addresses in a subnet. So, check your math versus the table in the answers section.

The lab does request that you configure the routers to match the plan. By doing so, and while also NOT using a routing protocol to learn routes, you can do some testing of your choices of IP addresses. However, to do a basic check, examine the ending configuration with the show running-config command to ensure the addresses and masks you intended to configure are in the configuration. Note that the masks should all be

Known Issues in this Lab

This section of each Config Lab Answers post hopes to help with those issues by listing any known issues with Packet Tracer related to this lab. In this case, the issues are:

# Summary Detail
1 None No known issues related to this lab.


Why Would Cisco Packet Tracer Have Issues?

(Note: The below text is the same in every Config Lab.)

Cisco Packet Tracer (CPT) simulates Cisco routers and switches. However, CPT does not run the same software that runs in real Cisco routers and switches. Instead, developers wrote CPT to predict the output a real router or switch would display given the same topology and configuration – but without performing all the same tasks, an actual device has to do. On a positive note, CPT requires far less CPU and RAM than a lab full of devices so that you can run CPT on your computer as an app. In addition, simulators like CPT help you learn about the Cisco router/switch user interface – the Command Line Interface (CLI) – without having to own real devices.

CPT can have issues compared to real devices because CPT does not run the same software as Cisco devices. CPT does not support all commands or parameters of a command. CPT may supply output from a command that differs in some ways from what an actual device would give. Those differences can be a problem for anyone learning networking technology because you may not have experience with that technology on real gear – so you may not notice the differences. So this section lists differences and issues that we have seen when using CPT to do this lab.

Beyond comparing your answers to this lab’s Answers post, you can test in Cisco Packet Tracer (CPT) or Cisco Modeling Labs (CML). In fact, you can and should explore the lab once configured. For this lab, once you have completed the configuration, try these verification steps. 

  1. Ping the IP address on the other end of each WAN link. To do so, from each router, try these steps:
    1. Login to that router and ping that router’s local IP addresses on its three interfaces – the ones you just configured. All the ping should work.
    2. Examine the figure, your notes about your planned IP addresses, and even the configuration on the other routers, to remind yourself of the IP addresses on the other end of the WAN links connected to the local router. EG, from R1, find R2’s IP address on its G0/1/0 port, and R3’s IP address on its G0/1/0 port.
    3. From the local router, ping the IP address on the other end of each WAN link. If you configured the address on the local and remote ends of the WAN link to be in the same subnet, the ping should work.
  2. Examine Connected Routes. From each router:
    1. Issue the show ip route command and focus on the connected routes only.
    2. Compare the command output to the figure for this lab. The figure lists the subnets and masks, and the command output should as well. Compare and ensure that the command output lists the same subnet IDs and masks shown in the figure.

More Labs with Related Content!

Config Lab: IPv4 Addresses 4
Config Lab: IPv4 Static Routes 1
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Benjamin Kinder

Hello Mr. Odom!

The figure depicting the topology (IP addresses and ports listed) and the table in this Config Lab don’t seem to match the answers given to me.

For example: GigabitEthernet ports are listed in the question, Serial and FastEthernet ports listed in the configuration answer.

Is it possible there is some kind of mismatch or am I gravely misunderstanding the nature of this exercise?

Thanks a ton for all your help!


Hi Benjamin,
Thanks for the note.
You are right to think it was non-sensical. Basically this one was missed in our QA checks – had the new revised details for the lab but the old details for the answers. Not a good combo.
I’ve taken a crack at fixing it. Let me know if it makes sense now or not.


The inferfaces for R3 in the answer and the exercise don’t match.

R3 G0/0
R3 G0/2/0
R3 G0/3/0

R3 G0/0 /26
R3 G0/1/0 /26
R3 G0/3/0


Thanks. I think I found and fixed them all. Configs were good, figures were good, tables listed the wrong interface IDs. thanks.


PC3 has improper settings, and as the answer doesn’t mention fixing them… maybe it should be added since it was a requirement of the question…


FastEthernet0 Connection:(default port)

Connection-specific DNS Suffix..:
Link-local IPv6 Address………: FE80::200:33FF:FE33:3333
IPv6 Address………………..: ::
IPv4 Address………………..:
Subnet Mask…………………:
Default Gateway……………..: ::

the ipv4 address should be

fixed with this command on PC3



Hello Wendell,
Please a question. I am going through this question from PTP and do not quite understand the explanation for the host route with two routes. Why will the route to server 2 not default to the floating route after the route with the better AD fails? I thought the concept of floating route is to take over if the route with the better AD fails? I have attached a screenshot of the question and posted the answer below:

This question has many details to work through, but before thinking about the answers, focus on the five ip route commands in the exhibit. Look for the two commands that list as the next-hop router address. Per the figure and question stem, R1’s G0/1 interface fails, which is the interface that leads to neighbor address
Continuing to look at the two ip route commands with as next-hop address, you can ignore one for this question because R1 will remove it from the routing table when R1’s G0/1 interface fails. However, the route in the ip route command with the permanent keyword remains in the IP routing table (because of the permanent keyword), even though the interface the route uses is down.
Next, move on to think about how a router uses the administrative distance (AD) of routes. IOS uses the AD as a tiebreaker when two competing routes have the exact same destination and prefix. In this case, two host routes list the exact same destination (, which is server S2) and exact same mask (, meaning both are host routes). One route does not list an AD, so it uses the default AD for static IP routes of 1. The other lists an AD of 140. So, on this decision point, IOS prefers the AD 1 route. Unfortunately, this one route (with the ip route permanent command) remains in the routing table even though the next-hop address is not reachable.
As a result of this analysis, packets sent to server S2 ( match the host route that uses as the next hop address. But because that address is not currently reachable, R1 discards the packet.
As for packets sent to server S1 (, only one of the five routes match the destinations as configured in the five ip route commands in the exhibit. One route configures a destination that comes close to matching address the ip route command. This command matches addresses– (Note that the figure lists server S1’s subnet as, so a correct static route for the entire subnet should have used dotted decimal mask So packets sent to server S1’s address will match the default route and be sent to router R4 ( next.

Ryley Trepagnier

I am either misunderstanding Rule #4 or I got the answer right ?

Rule #4 states that “Hosts should use the lowest IPv4 address in the subnet, with the same tiebreaker concept as stated in #2.”

Wouldn’t R1’s G 0/0 interface be instead of since 1 is lower than 62?

R2’s G0/0 interface should be /26 instead of /26

R3’s G0/0 interface should be /26 instead of /26

Please let me know if this is incorrect or not..?

I got the other interface IP addresses correct with the Router’s having the Highest IP address in the subnet w/ higher numbered Routers getting the higher IP address.

Ryley Trepagnier


Yes that makes sense, would R1-3 interfaces still use the lower number for the router’s interface towards the hosts or would that just apply to the host’s IP address themselves.

I comprehend that the interfaces are still on the router yet since it’s the path for the host to connect through the router, would the IP address on G0/0 R1 (for example) be the lowest address..?

(I choose to believe the host is a “tablet” in this lab haha!)


Ryley Trepagnier

Ryley Trepagnier

Hi Mr. Odom,

I understand since G0/0 is on R1, I guess i am trying to ask if that would effect end-to-end path, more or less. If it does, would the IP address on R1’s G0/0 interface need to reflect the host’s IP address?

Thank you for answering my obnoxious questions. These kinds of details help immensely sir .!



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