Config Lab: L3 EtherChannel 1

Wendell Odom
By Wendell Odom September 17, 2021 19:05

Layer 3 switches, SVIs, routed ports, and L3 EtherChannels. Those topics alone make this lab fairly advanced for CCNA prep. Today’s lab focuses on the L3 EtherChannel, but also gives you a chance to configure the rest of the features in the initial list as well.

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

Requirements

In this lab, you will add configuration to distribution switches Dist1 and Dist2. These two layer 3 switches will route packets for several subnets. Dist1 connects to the subnets supported by VLANs 10 and 20, while Dist2 connects to those supported by VLANs 30 and 40. The two distribution switches connect with a layer 3 EtherChannel with two links.

Your job: configure the SVIs (VLAN interfaces) necessary for routing the connected subnets on the access VLANs. The IP addresses on these SVIs will be used by the PCs in the network as their default gateway IP addresses. Then configure the layer 3 EtherChannel between the switches, providing a layer 3 link between the two distribution switches so that they can route packets to each other.

This lab begins with several key features pre-configured. Make sure to pay close attention to the initial configurations to get your bearings before starting to do the lab. These items are preconfigured:

  • The links connecting the Access switches with their Distribution switches are preconfigured as static trunks using 802.1q encapsulation.
  • The access and distribution switches have been pre-configured with the VLAN IDs listed in the figure.
  • All interfaces shown in the figure have been administratively enabled.
  • Layer 3 switches Dist1 and Dist2 have been pre-configured with OSPF so that once the lab has been configured, Dist1 and Dist2 will exchange IPv4 routes.

The following list details your work for this lab:

  • Configure Layer 3 switching with SVIs on the two distribution switches as follows:
    • Switch Dist1 routes for VLANs 10 and 20
    • Switch Dist2 routes for VLANs 30 and 40
  • Configure a layer 3 EtherChannel for the two links between switches Dist1 and Dist2 so that IPv4 packets can be routed between the two switches, as follows:
    • Configure the two links between the distribution switches as a static layer 3 EtherChannel with port-channel interface number 10.
    • Make the EtherChannel a routed port instead of a switch port.
    • Configure the IP addresses per the figure for the PortChannel interface

Figure 1: Switch Square w/L3 EtherChannel Topology

 

Initial Configuration

Examples 1, 2, 3, and 4 show the beginning configuration state of Dist1, Dist2, Access1, and Access2.

Example 1: Dist1 Config

 

Example 2: Dist2 Config

 

Example 3: Access1 Config

 

Example 4: Access2 Config

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 listed in the lab exercise documentation versus those used in the sample CML file.

Device Lab Port  CML Port
Dist1 G1/1/1 G0/1
Dist1 G1/1/2 G0/2
Dist1 G1/1/3 G0/3
Dist2 G1/1/1 G0/1
Dist2 G1/1/2 G0/2
Dist2 G1/1/3 G0/3
Access1 G1/1/1 G0/1
Access1 G1/0/2 G0/2
Access1 G1/0/3 G0/3
Access2 G1/1/1 G0/1
Access2 G1/0/2 G0/2
Access2 G1/0/3 G0/3

 

Host device info:

This table lists host information pre-configured in CML, information that might not be required by the lab but may be useful to you.

Device

IP Address

User/password

PC1

10.100.100.2/27

cisco/cisco

PC2

10.100.100.34/27

cisco/cisco

PC3

10.100.100.66/27

cisco/cisco

PC4

10.100.100.98/27

cisco/cisco

Lab Answers Below: Spoiler Alert

Lab Answers: Configuration (Click Tab to Reveal)

Answers

Figure 1: Switch Square w/L3 EtherChannel Topology

Example 5: Dist1 Config

 

Example 6: Dist2 Config

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

Commentary

In most modern networks, it has become standard that layer 3 switches are typically preferred over their router counterparts in the LAN. Layer 3 switches often support much higher packet forwarding volumes than routers of a similar price-point. Also, performing layer 3 forwarding inside a switch, versus Router-on-a-Stick, removes the trip over a cable to a router and back over the same cable to the switch. In modern enterprise networks, routers often sit only at the edge of the WAN, with switches connecting all the devices in a campus or a Data Center.

With this lab, you were tasked with configuring two distribution switches to act as layer 3 switches. Two access layer switches, operating only with layer 2 features, were pre-configured with those features and VLANs. Two two distribution switches act as the default gateway for the hosts in the VLANs shown in the figure.

First, looking at switch Dist1, it has three different interfaces. Two interfaces will be grouped together into a layer 3 EtherChannel link that connects to switch Dist2. Dist1’s other interface is the pre-configured trunk port that connects to switch Access1.

First, to configure the EtherChannel on the two links between the two distribution switches, you could start with the interface range gigabitethernet1/1/1 – 2 command so that upcoming interface subcommands would apply to both interfaces. Then add the no switchport command to convert the interfaces into a routed layer 3 interface and the channel-group 10 mode on command to group them together into an EtherChannel. Note that the channel-group command automatically creates the Port-Channel 10 interface.

The PortChannel interface also needs to be configured as a routed port, and then it also needs an IPv4 address. To do so, use the interface port-channel 10 command to get into interface config mode and configure the IP address using the ip address 100.1.2.1 255.255.255.240 command. Then add the no switchport command to make the port-channel interface a routed port.

The configuration of the L3 EtherChannel on switch Dist2 follows the same basic steps: configure the physical ports to be in the same channel-group (using the channel-group command), making the ports routed ports (no switchport), making the port-channel interface a routed port, and assigning the port-channel interface an IPv4 address.

To configure switch Dist1 to have a layer 3 interface connected to the subnets in VLANs 10 and 20, switch Dist1 must then configure VLAN interfaces 10 and 20. To configure the interface for VLAN 10, use the interface vlan 10 command, with an IP address configured with the ip address 10.100.100.1 255.255.255.224 command to match the information in the figure. Similarly, use the interface vlan 20 command and the ip address 10.100.100.33 255.255.255.224 command to configure the SVI for VLAN 20.

Switch Dist2 again follows a similar pattern, but for VLANs 30 and 40 in this case. To configure the VLAN 30 interface, use the interface vlan 30 command, and to configure the IP address, use the ip address 10.100.100.65 255.255.255.224 command. To configure the VLAN 40 interface, use the interface vlan 40 command, and to configure its IP address, use the ip address 10.100.100.97 255.255.255.224 command.

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. Check that the VLANs have been created using the show vlan brief and show interfaces interface switchport commands on the distribution switches.
  2. Check that the VLAN interfaces were configured with the show ip interfaces brief and/or show running-config commands.
  3. Check that the trunks are operational using the show interfaces trunk command.

 

For the layer 3 specifics, check on the L3 EtherChannel, the SVIs, and make sure OSPF is working:

  1. Verify the state of the L3 EtherChannel using the show etherchannel summary command.
  2. Check the port-channel interface using the show interfaces port-channel10 command.
  3. The show interfaces status command should list the physical ports in the channel and interface portchannel10 as a routed port rather than being assigned to a VLAN.
  4. Also, each distribution (layer 3) switch should list three connected IPv4 routes in the output of the show ip route command.

More Labs with Related Content!

Config Lab: Layer 3 Switching w/ Routed Ports
Config Lab: OSPF Interface Config 1
Wendell Odom
By Wendell Odom September 17, 2021 19:05
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2 Comments

  1. Emil February 7, 18:35

    Am I the only one who sees yellow dots on the interfaces that are part of the etherchannel in packet tracer? My version is 8.1.0.0722.

    Reply to this comment
    • Clear February 15, 07:06

      I see those dots too. I think it’s PacketTracer’s way of denoting that not all the interfaces are “up” in the way that individual interfaces would be.

      Reply to this comment
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