Layer 3 EtherChannel
Course Contents
1. Introduction
In the previous lesson, you bundled multiple switch ports into one logical link with Layer 2 EtherChannel.
Now we move on to Layer 3 EtherChannel. The idea is the same: combine several physical interfaces into one Port-Channel. The difference is that the Port-Channel is treated as a routed interface and can be assigned an IP address instead of functioning as a switchport.
This type of configuration is supported on multilayer switches and routers. In Cisco’s three-tier design (Access → Distribution → Core), it is commonly used between the Distribution and Core layers to ensure reliable, high-bandwidth interconnections.
In this lab, two multilayer switches (SW1 and SW2) will bundle interfaces F0/1 and F0/2 into Port-Channel 1.
Each Port-Channel interface will then be assigned an IP address from the 192.168.1.0/24 network.
Let’s dive into the configuration.
2. Layer 3 EtherChannel Configuration
Step 1 – Enable IP Routing
Since we are working with multilayer switches, we must first activate the global routing function.
By default, these devices can operate only at Layer 2. With the command ip routing, we tell the switch to forward packets based on IP addresses.
SW1# configure terminal Enter configuration commands, one per line. End with CNTL/Z. SW1(config)# ip routing SW2# configure terminal Enter configuration commands, one per line. End with CNTL/Z. SW2(config)# ip routing
At this point, both switches are ready to handle Layer 3 interfaces. The next step is to convert the physical ports that will participate in the EtherChannel into routed interfaces.
Step 2 – Convert Interfaces to Routed Ports and Create the Port-Channel
We select interfaces F0/1 and F0/2 on each switch.
- The command
no switchportchanges them from Layer 2 switchports to Layer 3 routed ports. - Then, with
channel-group 1 mode on, we bundle them into Port-Channel 1.
Here we use mode on, which creates a static EtherChannel without negotiation protocols (no PAgP or LACP). This is simple and reliable for a lab environment.
SW1(config)# interface range f0/1-2 SW1(config-if-range)# no switchport SW1(config-if-range)# channel-group 1 mode on Creating a port-channel interface Port-channel 1 SW2(config)# interface range f0/1-2 SW2(config-if-range)# no switchport SW2(config-if-range)# channel-group 1 mode on Creating a port-channel interface Port-channel 1
At this stage, the two physical interfaces are grouped, and the system has automatically created the logical interface Port-Channel 1.
Step 3 – Assign IP Addresses to the Port-Channel Interface
Now that the port-channel exists, we configure it as a routed interface. This means applying an IP address directly to the logical Port-Channel interface rather than the physical ones.
- On SW1 we use
192.168.1.1/24. - On SW2 we use
192.168.1.2/24.
SW1(config)# interface port-channel 1 SW1(config-if)# ip address 192.168.1.1 255.255.255.0 SW1(config-if)# no shutdown SW2(config)# interface port-channel 1 SW2(config-if)# ip address 192.168.1.2 255.255.255.0 SW2(config-if)# no shutdown
At this point, both switches are connected through a Layer 3 EtherChannel. The logical Port-Channel interface carries the IP address, while the physical interfaces F0/1 and F0/2 work together in parallel, providing redundancy and additional bandwidth.
3. Verification
After completing the configuration, it is important to confirm that the Layer 3 EtherChannel is active and functioning correctly.
Check EtherChannel Summary
Use the show etherchannel summary command to get an overview of the EtherChannel:
SW1# show etherchannel summary
Flags: D - down P - in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator
u - unsuitable for bundling
w - waiting to be aggregated
d - default port
Number of channel-groups in use: 1
Number of aggregators: 1
Group Port-channel Protocol Ports
------+-------------+-----------+----------------------------------------------
1 Po1(RU) - Fa0/1(P) Fa0/2(P)
Explanation
- RU → The Port-Channel is Routed (R) and Up (U).
- P → Interfaces F0/1 and F0/2 are successfully bundled in the EtherChannel.
This confirms that the EtherChannel on SW1 is working properly.
The same check on SW2 gives an identical result:
SW2# show etherchannel summary
Flags: D - down P - in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator
u - unsuitable for bundling
w - waiting to be aggregated
d - default port
Number of channel-groups in use: 1
Number of aggregators: 1
Group Port-channel Protocol Ports
------+-------------+-----------+----------------------------------------------
1 Po1(RU) - Fa0/1(P) Fa0/2(P)
Both outputs confirm that Port-Channel 1 is operational and the two interfaces are correctly aggregated.
Check IP Interfaces
Now let’s verify the IP configuration with show ip interface brief.
SW1# show ip int brief Interface IP-Address OK? Method Status Protocol Port-channel1 192.168.1.1 YES manual up up FastEthernet0/1 unassigned YES unset up up FastEthernet0/2 unassigned YES unset up up SW2# show ip int brief Interface IP-Address OK? Method Status Protocol Port-channel1 192.168.1.2 YES manual up up FastEthernet0/1 unassigned YES unset up up FastEthernet0/2 unassigned YES unset up up
Both Port-Channel interfaces are up with the correct IP addresses, while the physical interfaces are unassigned (as expected).
Ping Test
Since we want to confirm that the Layer 3 EtherChannel is working as expected, we perform a connectivity test using a ping.
We send a ping from SW1 to the IP address of the Layer 3 EtherChannel interface on SW2 (192.168.1.2):
SW1# ping 192.168.1.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 0/0/0 ms
The ping is successful, confirming that the Layer 3 EtherChannel is up and operational.
4. Conclusion
Layer 3 EtherChannel combines multiple physical interfaces into a single logical routed interface.
Unlike Layer 2 EtherChannel, which works as a switchport, the Layer 3 Port-Channel is assigned an IP address and can participate in routing.
Configuration Summary
Step 1 – Enable IP Routing SW1(config)# ip routing SW2(config)# ip routing Step 2 – Convert Interfaces & Create Port-Channel SW1(config)# interface range f0/1-2 SW1(config-if-range)# no switchport SW1(config-if-range)# channel-group 1 mode on SW2(config)# interface range f0/1-2 SW2(config-if-range)# no switchport SW2(config-if-range)# channel-group 1 mode on Step 3 – Assign IP Address to Port-Channel SW1(config)# interface port-channel 1 SW1(config-if)# ip address 192.168.1.1 255.255.255.0 SW1(config-if)# no shutdown SW2(config)# interface port-channel 1 SW2(config-if)# ip address 192.168.1.2 255.255.255.0 SW2(config-if)# no shutdown