In this post, I would like to show you how to configure LACP on Cisco switches. LACP is a dynamic link aggregation protocol which helps create an EtherChannel port on Cisco switches.
An EtherChannel interface is the result of bundling multiple physical links into a logical port. It is recommended to use n links to the power of two (For example 2, 4, 8, 16 physical ports). In other technical documents, you can find references to the same concept by the name port-channel, link aggregation group (LAG), and bonding.
The idea behind this concept is to increase the fault tolerance and speed between switches, routers and/or servers. In case of a link failure, the traffic will be redistributed among the remaining links.
Link Aggregation Control Protocol (LACP) was standardized by the Institute of Electrical and Electronics Engineers (IEEE) and is defined in 802.3AD link aggregation specification. It is an open standard as oposed to PAgP which is a Cisco proprietary protocol. It is used for dynamically establishing an EtherChannel port on Cisco switches and/or other devices. This protocol can be used in a mixed environment. It is supported by multiple network equipment vendors.
Table of Contents
Check the interface status
Before starting to configure EtherChannel, let’s check the lab network diagram and the interfaces status. I will use 4 interfaces in my lab. All of them are in connected status.
Output SW0:
SW0#show int status
Port Name Status Vlan Duplex Speed Type
Gi0/0 connected trunk a-full auto RJ45
Gi0/1 connected trunk a-full auto RJ45
Gi0/2 connected trunk a-full auto RJ45
Gi0/3 connected trunk a-full auto RJ45
Gi1/0 connected 10 a-full auto RJ45
SW0#Output SW1:
SW1#show int status
Port Name Status Vlan Duplex Speed Type
Gi0/0 connected trunk a-full auto RJ45
Gi0/1 connected trunk a-full auto RJ45
Gi0/2 connected trunk a-full auto RJ45
Gi0/3 connected trunk a-full auto RJ45
Gi1/0 connected 10 a-full auto RJ45
SW1#
Check spanning-tree
If you add multiple links between two switches, spanning tree will block all the links and leave only one link for traffic forwarding. With EtherChannel this is not the case. Let’s check if all the interfaces are used to forward the traffic.
Output SW0:
SW0#show spanning-tree vlan 1
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 5254.000b.a5e5
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 5254.000b.a5e5
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/0 Desg FWD 4 128.1 P2p
Gi0/1 Desg FWD 4 128.2 P2p
Gi0/2 Desg FWD 4 128.3 P2p
Gi0/3 Desg FWD 4 128.4 P2p
SW0#Output SW1:
SW1#show spanning-tree vlan 1
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 5254.000b.a5e5
Cost 4
Port 1 (GigabitEthernet0/0)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 5254.0011.9ff1
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/0 Root FWD 4 128.1 P2p
Gi0/1 Altn BLK 4 128.2 P2p
Gi0/2 Altn BLK 4 128.3 P2p
Gi0/3 Altn BLK 4 128.4 P2p
SW1#
As you can see on SW1, from the available 4 ports, only one is in forwarding status. The other 3 are in blocking status. I will share the same output after adding the ports to the EtherChannel bundle.
Configure LACP
After confirming that all ports are up and running, you need to configure LACP by running the below commands.
Output SW0:
SW0#conf term
Enter configuration commands, one per line. End with CNTL/Z.
SW0(config)#int range gi0/0-3
SW0(config-if-range)#chan
SW0(config-if-range)#channel-gr
SW0(config-if-range)#channel-group 1 mode ?
active Enable LACP unconditionally
auto Enable PAgP only if a PAgP device is detected
desirable Enable PAgP unconditionally
on Enable Etherchannel only
passive Enable LACP only if a LACP device is detected
SW0(config-if-range)#channel-group 1 mode ac
SW0(config-if-range)#channel-group 1 mode active
Creating a port-channel interface Port-channel 1
SW0(config-if-range)#
*Jul 17 11:38:32.097: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0, changed state to down
*Jul 17 11:38:32.130: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/1, changed state to down
*Jul 17 11:38:32.156: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/2, changed state to down
*Jul 17 11:38:32.197: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/3, changed state to down
SW0(config-if-range)#
*Jul 17 11:38:39.424: %EC-5-L3DONTBNDL2: Gi0/2 suspended: LACP currently not enabled on the remote port.
*Jul 17 11:38:39.483: %EC-5-L3DONTBNDL2: Gi0/0 suspended: LACP currently not enabled on the remote port.
*Jul 17 11:38:39.632: %EC-5-L3DONTBNDL2: Gi0/3 suspended: LACP currently not enabled on the remote port.
*Jul 17 11:38:39.648: %EC-5-L3DONTBNDL2: Gi0/1 suspended: LACP currently not enabled on the remote port.
SW0(config-if-range)#Output SW1:
SW1#conf term
*Jul 17 11:37:50.678: %SYS-5-CONFIG_I: Configured from console by console
SW1#conf term
Enter configuration commands, one per line. End with CNTL/Z.
SW1(config)#int range gi0/0-3
SW1(config-if-range)#channe
SW1(config-if-range)#channel-gr
SW1(config-if-range)#channel-group 1 mode ?
active Enable LACP unconditionally
auto Enable PAgP only if a PAgP device is detected
desirable Enable PAgP unconditionally
on Enable Etherchannel only
passive Enable LACP only if a LACP device is detected
SW1(config-if-range)#channel-group 1 mode pass
SW1(config-if-range)#channel-group 1 mode passive
SW1(config-if-range)#
*Jul 17 11:39:16.235: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0, changed state to down
*Jul 17 11:39:16.260: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/1, changed state to down
*Jul 17 11:39:16.290: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/2, changed state to down
*Jul 17 11:39:16.320: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/3, changed state to down
SW1(config-if-range)#
*Jul 17 11:39:19.559: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/3, changed state to up
*Jul 17 11:39:20.516: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/1, changed state to up
SW1(config-if-range)#
*Jul 17 11:39:20.587: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/2, changed state to up
SW1(config-if-range)#
*Jul 17 11:39:22.682: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0, changed state to up
SW1(config-if-range)#
*Jul 17 11:39:29.019: %LINK-3-UPDOWN: Interface Port-channel1, changed state to up
SW1(config-if-range)#
*Jul 17 11:39:30.019: %LINEPROTO-5-UPDOWN: Line protocol on Interface Port-channel1, changed state to up
SW1(config-if-range)#I used the interface range command in order to configure multiple interfaces at the same time.
LACP port modes
LACP port modes:
active – Enable LACP unconditionally. The interface transmits LACP packets out of it and initiates an EtherChannel to be established.
passive – Enable LACP only if a LACP device is detected. The interface does not initiate an EtherChannel to be established and does not transmit LACP packets out of it.
You need to configure at least one end of the interface with the active mode. Otherwise, it will not work and the port channel will remain down.
SW0#show etherchannel summ
SW0#show etherchannel summary
Flags: D - down P - bundled in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use N - not in use, no aggregation
f - failed to allocate aggregator
M - not in use, minimum links not met
m - not in use, port not aggregated due to minimum links not met
u - unsuitable for bundling
w - waiting to be aggregated
d - default port
A - formed by Auto LAG
Number of channel-groups in use: 1
Number of aggregators: 1
Group Port-channel Protocol Ports
------+-------------+-----------+-----------------------------------------------
1 Po1(SU) LACP Gi0/0(P) Gi0/1(P) Gi0/2(P)
Gi0/3(P)
SW0#
Check the status of the newly created logical interface
After configuring both switches, you need to check the status of the newly created logical interface.
Run a similar command for finding details about the new interface.
Output SW0:
SW0#show int po1
Port-channel1 is up, line protocol is up (connected)
Hardware is EtherChannel, address is 5254.000b.a5e5 (bia 5254.000b.a5e5)
MTU 1500 bytes, BW 4000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:28:10, output never, output hang never
Last clearing of "show interface" counters never
Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 1000 bits/sec, 2 packets/sec
245 packets input, 84198 bytes, 0 no buffer
Received 0 broadcasts (0 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 input packets with dribble condition detected
3443 packets output, 345882 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier
0 output buffer failures, 0 output buffers swapped out
SW0#Output SW1:
SW1#show int po1
Port-channel1 is up, line protocol is up (connected)
Hardware is EtherChannel, address is 5254.000d.b77b (bia 5254.000d.b77b)
MTU 1500 bytes, BW 4000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output never, output hang never
Last clearing of "show interface" counters never
Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 1000 bits/sec, 1 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
2698 packets input, 232394 bytes, 0 no buffer
Received 0 broadcasts (0 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 input packets with dribble condition detected
832 packets output, 170604 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier
0 output buffer failures, 0 output buffers swapped out
SW1#The logical interface on both switches is in up status.
As you can see, the available bandwith has increased from 1000000 Kbit/sec to 4000000 Kbit/sec.
LACP show commands
By running the show lacp neighbour command, you can find more details about the neighbor device. You can find the priority of the interfaces, the ID of the neighbour device and you can find which mode the neighbour interface is in (active or passive).
SW0#show lacp nei
SW0#show lacp neighbor
Flags: S - Device is requesting Slow LACPDUs
F - Device is requesting Fast LACPDUs
A - Device is in Active mode P - Device is in Passive mode
Channel group 1 neighbors
Partner's information:
LACP port Admin Oper Port Port
Port Flags Priority Dev ID Age key Key Number State
Gi0/0 SP 32768 5254.0011.8000 19s 0x0 0x1 0x1 0x3C
Gi0/1 SP 32768 5254.0011.8000 25s 0x0 0x1 0x2 0x3C
Gi0/2 SP 32768 5254.0011.8000 8s 0x0 0x1 0x3 0x3C
Gi0/3 SP 32768 5254.0011.8000 0s 0x0 0x1 0x4 0x3C
SW0#
To find the number of the lacp packets sent and received, run the following command.
SW0#show lacp counters
LACPDUs Marker Marker Response LACPDUs
Port Sent Recv Sent Recv Sent Recv Pkts Err
---------------------------------------------------------------------
Channel group: 1
Gi0/0 92 95 0 0 0 0 0
Gi0/1 290 287 0 0 0 0 0
Gi0/2 92 94 0 0 0 0 0
Gi0/3 92 95 0 0 0 0 0
SW0#
Finally, to find the local system id, run the following command.
SW0#show lacp sys
SW0#show lacp sys-id
1, 5254.000b.8000
SW0#
Check if STP is blocking the ports
After confirming that the logical interface is up and running, let’s check if STP is blocking any interface. Before configuring EtherChannel, it blocked 3 interfaces.
Output SW0:
SW0#show spanning-tree vlan 1
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 5254.000b.a5e5
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 5254.000b.a5e5
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Po1 Desg FWD 3 128.65 P2p
SW0#Output SW1:
SW1#show spanning-tree vlan 1
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 5254.000b.a5e5
Cost 3
Port 65 (Port-channel1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 5254.0011.9ff1
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Po1 Root FWD 3 128.65 P2p
SW1#The EtherChannel interface is in forwarding status. The physical interfaces that are part of the logical interface are no longer present in the output.
The speed of the interface is increased to 4000000 Kbit/sec.
SW1#show int po1 | include line|BW
Port-channel1 is up, line protocol is up (connected)
MTU 1500 bytes, BW 4000000 Kbit/sec, DLY 10 usec,
SW1#
Find more details about the EtherChannel port
Another two useful commands that you can use in order to find more information about the EtherChannel ports are:
SW0#show etherchannel
Channel-group listing:
----------------------
Group: 1
----------
Group state = L2
Ports: 4 Maxports = 4
Port-channels: 1 Max Port-channels = 4
Protocol: LACP
Minimum Links: 0
SW0#In the output of the show etherchannel command, you can find the group number (1 in my case), and group state (L2, it can be also configured as L3). You have the number of ports which are part of the logical interface (4 in my lab). Under the protocol, you see LACP because we configured the EtherChannel dynamically using the Link Aggregation Control Protocol.
SW1#show etherchannel summary
Flags: D - down P - bundled in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use N - not in use, no aggregation
f - failed to allocate aggregator
M - not in use, minimum links not met
m - not in use, port not aggregated due to minimum links not met
u - unsuitable for bundling
w - waiting to be aggregated
d - default port
A - formed by Auto LAG
Number of channel-groups in use: 1
Number of aggregators: 1
Group Port-channel Protocol Ports
------+-------------+-----------+-----------------------------------------------
1 Po1(SU) LACP Gi0/0(P) Gi0/1(P) Gi0/2(P)
Gi0/3(P)
SW1#In the output of the show etherchannel summary command, you can find the following information: group number, port-channel name and its status (SU – Layer 2, in use), member ports and their status (P – bundled in port-channel) and the protocol used (LACP in our case).
Check the connectivity from PC0 to PC1
The last step is to check the connectivity between the end hosts: PC0 and PC1.
With the ping command, I tested the connectivity between PC0 and PC1.
Alpine-0:~$ ping -c 4 10.1.1.20
PING 10.1.1.20 (10.1.1.20): 56 data bytes
64 bytes from 10.1.1.20: seq=0 ttl=42 time=18.751 ms
64 bytes from 10.1.1.20: seq=1 ttl=42 time=20.956 ms
64 bytes from 10.1.1.20: seq=2 ttl=42 time=16.420 ms
64 bytes from 10.1.1.20: seq=3 ttl=42 time=16.381 ms
--- 10.1.1.20 ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 16.381/18.127/20.956 ms
Alpine-0:~$
Alpine-0:~$ 
That’s it! You have learned how to configure LACP on Cisco switches. If you found this blog post helpful, please like and subscribe for more Cisco networking tutorials. Thank you for reading it!