Cisco Nexus LACP Port-Channel Configuration Guide
This is Part 3 of the Cisco Nexus NX-OS configuration series. In this lab, we will configure dynamic Port-Channels using LACP between:
- NX-01 and NX-02
- NX-01 and NX-03
Unlike Part 2 where we used static mode ON, this lab introduces LACP which is the modern and recommended EtherChannel protocol.
Previous Parts
- Part 1 - Cisco Nexus VLAN and Trunk Configuration
- Part 2 - Cisco Nexus Static Port-Channel Configuration
Next Part
Table of Contents
- 1. Introduction to LACP
- 2. Task 1 - Configure Port-Channel 12
- 3. Task 2 - Configure Port-Channel 12 as Trunk
- 4. Task 3 - Verify Port-Channel 12
- 5. Task 4 - Configure Port-Channel 13
- 6. Task 5 - Configure Port-Channel 13 as Trunk
- 7. Task 6 - Verify Port-Channel 13
- 8. LACP Concepts Explained
- 9. EtherChannel Mathematics
- 10. Static vs LACP Comparison
- 11. Modern Data Center Best Practices
- 12. Troubleshooting
- 13. Related Articles
1. Introduction to LACP
LACP stands for:
Link Aggregation Control Protocol
LACP is an IEEE standard protocol defined under:
\[ IEEE\ 802.3ad \]
Modern implementations also reference:
\[ IEEE\ 802.1AX \]
Why LACP is Better Than Static EtherChannel
- Automatic negotiation
- Consistency validation
- Failure detection
- Dynamic member management
- Improved scalability
- Industry standard interoperability
How LACP Works
LACP exchanges packets called:
LACPDU (LACP Data Units)
These packets help:
- Discover neighbors
- Validate compatibility
- Form Port-Channels dynamically
2. Task 1 - Configure Port-Channel 12
We will configure:
- NX-01 E1/1-2
- NX-02 E1/1-2
These interfaces will become:
\[ Port\text{-}Channel\ 12 \]
Enable LACP Feature
NX-OS uses modular features. Before configuring LACP, we must enable it.
NX-01 Configuration
configure terminal
feature lacp
interface ethernet1/1-2
channel-group 12 mode active
no shutdown
end
copy running-config startup-config
NX-02 Configuration
configure terminal
feature lacp
interface ethernet1/1-2
channel-group 12 mode active
no shutdown
end
copy running-config startup-config
What Does Mode Active Mean?
LACP has two operational modes:
| Mode | Behavior |
|---|---|
| Active | Sends LACP packets actively |
| Passive | Waits for LACP packets |
Best practice:
\[ Active + Active \]
This ensures faster Port-Channel establishment.
3. Task 2 - Configure Port-Channel 12 as Trunk
After forming the Port-Channel, configure the logical interface as a trunk.
NX-01 Configuration
configure terminal
interface port-channel12
switchport
switchport mode trunk
no shutdown
end
NX-02 Configuration
configure terminal
interface port-channel12
switchport
switchport mode trunk
no shutdown
end
Verification Example
Click to Expand CLI Output
NX-01# show running-config interface port-channel12 interface port-channel12 switchport switchport mode trunk no shutdown
4. Task 3 - Verify Port-Channel 12
Verification is extremely important in networking.
Verification Command
show port-channel summary
Expected Output
Click to Expand Verification Output
NX-01# show port-channel summary
Flags: D - Down
P - Up in port-channel
Group Port-Channel Type Protocol Member Ports
-----+------------+----+--------+--------------------
12 Po12(SU) Eth LACP Eth1/1(P) Eth1/2(P)
5. Task 4 - Configure Port-Channel 13
Now we will configure another dynamic EtherChannel:
- NX-01 E1/3-4
- NX-03 E1/1-2
This will form:
\[ Port\text{-}Channel\ 13 \]
NX-01 Configuration
configure terminal
feature lacp
interface ethernet1/3-4
channel-group 13 mode active
no shutdown
end
copy running-config startup-config
NX-03 Configuration
configure terminal
feature lacp
interface ethernet1/1-2
channel-group 13 mode active
no shutdown
end
copy running-config startup-config
Notice:
The original text mentioned:
channel-group 12 mode active
on NX-03, but this appears to be a typo. Since the Port-Channel must be:
\[ Port\text{-}Channel\ 13 \]
the correct command should be:
channel-group 13 mode active
6. Task 5 - Configure Port-Channel 13 as Trunk
NX-01 Configuration
configure terminal
interface port-channel13
switchport
switchport mode trunk
no shutdown
end
NX-03 Configuration
configure terminal
interface port-channel13
switchport
switchport mode trunk
no shutdown
end
7. Task 6 - Verify Port-Channel 13
Verification Command
show port-channel summary
Expected Output
Click to Expand Verification Output
NX-03# show port-channel summary
Flags: D - Down
P - Up in port-channel
Group Port-Channel Type Protocol Member Ports
-----+------------+----+--------+--------------------
13 Po13(SU) Eth LACP Eth1/1(P) Eth1/2(P)
8. LACP Concepts Explained
LACP States
| State | Description |
|---|---|
| Active | Initiates LACP negotiation |
| Passive | Responds to LACP negotiation |
| Individual | Not participating in Port-Channel |
| Bundled | Successfully joined EtherChannel |
LACP System Priority
LACP selects the controlling device using:
\[ Lowest\ System\ Priority \]
Example:
\[ SwitchA = 32768 \]
\[ SwitchB = 100 \]
SwitchB becomes preferred because:
\[ 100 < 32768 \]
9. EtherChannel Mathematics
Bandwidth Aggregation
If:
\[ n = Number\ of\ Links \]
\[ B = Bandwidth\ per\ Link \]
Then:
\[ Total\ Bandwidth = n \times B \]
Example:
\[ n = 2 \]
\[ B = 10Gbps \]
\[ Total = 2 \times 10 \]
\[ Total = 20Gbps \]
Traffic Distribution Formula
LACP distributes flows using hashing:
\[ Hash = f(SourceIP + DestinationIP) \]
The resulting value determines:
- Which physical link carries traffic
- How flows are balanced
Efficiency Gain
Suppose:
\[ Single\ Link = 10Gbps \]
Port-Channel:
\[ 2 \times 10Gbps \]
Result:
\[ 20Gbps \]
Bandwidth doubles while maintaining redundancy.
10. Static vs LACP Comparison
| Feature | Static Mode ON | LACP |
|---|---|---|
| Negotiation | No | Yes |
| Error Detection | Minimal | Advanced |
| Industry Standard | No | Yes |
| Scalability | Limited | Better |
| Modern Recommendation | No | Yes |
11. Modern Data Center Best Practices
Modern Nexus deployments usually include:
- vPC
- VXLAN EVPN
- Automation
- Ansible
- Terraform
- Streaming telemetry
Modern NX-OS Best Practice Example
configure terminal
feature lacp
interface ethernet1/1-2
description UPLINK_TO_NX02
channel-group 12 mode active
no shutdown
interface port-channel12
description LACP_UPLINK_TO_NX02
switchport
switchport mode trunk
switchport trunk allowed vlan 10,20
spanning-tree port type network
no shutdown
12. Troubleshooting
Problem: Port-Channel Down
Possible causes:
- LACP disabled
- Speed mismatch
- Trunk mismatch
- Different VLAN lists
- Incorrect channel-group numbers
Verification Commands
show port-channel summary
show lacp neighbor
show interface status
show spanning-tree
show running-config interface port-channel12
Check LACP Neighbors
Click to Expand LACP Neighbor Output
NX-01# show lacp neighbor
Flags: S - Device is requesting Slow LACPDUs
F - Device is requesting Fast LACPDUs
Channel group 12 neighbors
Partner's information:
LACP port Admin Oper Port Port
Port Flags Priority Dev ID Age key Key Number State
Eth1/1 SA 32768 001b.0c00.1111 15s 0x0 0x1 0x101 0x3d
Complete Final Configuration
configure terminal
feature lacp
interface ethernet1/1-2
channel-group 12 mode active
no shutdown
interface port-channel12
switchport
switchport mode trunk
no shutdown
interface ethernet1/3-4
channel-group 13 mode active
no shutdown
interface port-channel13
switchport
switchport mode trunk
no shutdown
end
copy running-config startup-config
Key Takeaways
✔ LACP is the preferred modern EtherChannel protocol.
✔ LACP dynamically negotiates Port-Channels using LACPDUs.
✔ Active mode actively sends negotiation packets.
✔ Port-Channels increase both bandwidth and redundancy.
✔ Configuration should be applied on the logical Port-Channel interface.
✔ Always verify Port-Channel status after configuration.
Conclusion
In this Cisco Nexus LACP configuration guide, we configured dynamic Port-Channels between NX-01, NX-02, and NX-03 using LACP.
We configured:
- Port-Channel 12
- Port-Channel 13
- Trunking on logical Port-Channels
- LACP negotiation using active mode
- Verification and troubleshooting commands
Understanding LACP is extremely important because modern enterprise and data center networks rely heavily on dynamic EtherChannel technologies for scalability, redundancy, and performance optimization.
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