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Link Aggregation Control Protocol (LACP)

LACP (IEEE 802.3ad) aggregates multiple physical links into one logical interface called a port-channel, increasing total bandwidth and providing failover protection. All member interfaces must match in speed, duplex, MTU, and link type.

Topology​

Each switch contributes two 10G links. LACP combines them into a single 20 Gbps logical channel.
Tested with DeLL Force10

Switch A Configuration​

Port-Channel Creation​

Create the logical bundle first.

Input:

interface port-channel 3
description lacp-distribution
info

Optional configuration:​

  • If this is a Layer 3 port-channel, add:

    no switchport
    ip address <IP> <MASK>

  • If using static (non-LACP):

    port-channel 3 mode on
    Not recommended unless connecting to a device without LACP.

  • If needing fast LACP timers:

    lacp rate fast

    30s → 1s heartbeat

Physical Member Ports​

Te 0/1​

Input:

interface te 0/1
no switchport
no shutdown
description lacp3-core
port-channel-protocol lacp
port-channel 3 mode active

Output:

  • Interface becomes routed (L3) if supported.
  • Joins LACP Port-channel 3 in active LACP negotiation mode.
info

Optional configuration:​

  • If you want passive LACP mode (waits for peer, more conservative): 
    port-channel 3 mode passive
  • If you want Layer2 only, remove no switchport: 
    switchport

Te 0/2​

Same settings as Te0/1.

Input:

interface te 0/2
no switchport
no shutdown
description lacp3-core
port-channel-protocol lacp
port-channel 3 mode active

Switch B Configuration​

Configuration mirrors Switch A.

Port-Channel Creation​

Input:

interface port-channel 3
description lacp-distribution

Physical Member Ports​

Te 0/1​

Input:

interface te 0/1
no switchport
no shutdown
description lacp3-core
port-channel-protocol lacp
port-channel 3 mode active

Te 0/2​

Input:

interface te 0/2
no switchport
no shutdown
description lacp3-core
port-channel-protocol lacp
port-channel 3 mode active

Verification Commands​

Port-Channel Summary​

Input:

show interfaces port-channel 3 brief

Output:

Codes: L - LACP Port-channel

    LAG Mode  Status       Uptime      Ports          
L   3   L2    up           29w5d14h    Te 0/1    (Up)
                                       Te 0/2    (Up)
info
  • Port-channel is up.
  • Both physical links are operational and negotiated via LACP.

Detailed Port-Channel State​

Input:

show interfaces port-channel 3

Output:

Port-channel 3 is up, line protocol is up
Created by LACP protocol
Description: lacp3-core
LineSpeed 20000 Mbit
Members in this channel:  Te 0/1(U) Te 0/2(U)
info
  • Bundle total bandwidth = 20G (2 × 10G).
  • Both interfaces show U = In Use.

Decision Logic & Optional Behavior​

If you want to enforce symmetric hashing (better load balance):​

port-channel load-balance src-dst-ip

If connecting to a device without LACP support:​

Use static mode:

port-channel 3 mode on

If you need rapid failover:​

lacp rate fast

Check:

show lacp counters
show log

If member interfaces refuse to join:​

Common mismatches:

  • switchport vs no switchport
  • speed/duplex mismatches
  • port-channel mode mismatch (active vs on)
  • LACP not enabled on peer