Troubleshoot Link Aggregation Control Protocol (LACP) on Nexus

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Updated:October 5, 2023

Document ID:221051

Bias-Free Language

The documentation set for this product strives to use bias-free language. For the purposes of this documentation set, bias-free is defined as language that does not imply discrimination based on age, disability, gender, racial identity, ethnic identity, sexual orientation, socioeconomic status, and intersectionality. Exceptions may be present in the documentation due to language that is hardcoded in the user interfaces of the product software, language used based on RFP documentation, or language that is used by a referenced third-party product. Learn more about how Cisco is using Inclusive Language.

Introduction

This document describes how to troubleshoot Link Aggregation Control Protocol (LACP) on Nexus 9000 cloudscale family.

Prerequisites

Requirements

Cisco recomends that you have knowledge of these topics:

LACP protocol
NXOS Platform
ELAM understanding
Ethanalyzer understanding

Components Used

Name	Paltform	Version
N9K1	N9K-C93108TC-EX	9.3(10)
N9K2	N9K-C93108TC-EX	9.3(10)

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, ensure that you understand the potential impact of any command.

Topology

Network diagram

Verify LACP Link Status

Network diagram user interface

Note: Image 1.1 LACP link status.

Configure LACP:

N9K1 N9K2

show run interface port-channel 1 membership 

interface port-channel1
  switchport
  switchport mode trunk

interface Ethernet1/1
  switchport
  switchport mode trunk
  channel-group 1 mode active
  no shutdown

interface Ethernet1/2
  switchport
  switchport mode trunk
  channel-group 1 mode active
  no shutdown

show run interface port-channel 1 membership 

interface port-channel1
  switchport
  switchport mode trunk

interface Ethernet1/1
  switchport
  switchport mode trunk
  channel-group 1 mode active
  no shutdown

interface Ethernet1/2
  switchport
  switchport mode trunk
  channel-group 1 mode active
  no shutdown

Verify port-channel status

N9K1 N9K2

sh port-channel summary interface port-channel 1
Flags:  D - Down        P - Up in port-channel (members)
        I - Individual  H - Hot-standby (LACP only)
        s - Suspended   r - Module-removed
        b - BFD Session Wait
        S - Switched    R - Routed
        U - Up (port-channel)
        p - Up in delay-lacp mode (member)
        M - Not in use. Min-links not met
--------------------------------------------------------------------------------
Group Port-       Type     Protocol  Member Ports
      Channel
--------------------------------------------------------------------------------
1     Po1(SU)     Eth      LACP      Eth1/1(P)

sh port-channel summary interface port-channel 1
Flags:  D - Down        P - Up in port-channel (members)
        I - Individual  H - Hot-standby (LACP only)
        s - Suspended   r - Module-removed
        b - BFD Session Wait
        S - Switched    R - Routed
        U - Up (port-channel)
        p - Up in delay-lacp mode (member)
        M - Not in use. Min-links not met
--------------------------------------------------------------------------------
Group Port-       Type     Protocol  Member Ports
      Channel
--------------------------------------------------------------------------------
1     Po1(SU)     Eth      LACP      Eth1/1(P)

Note: Most common failure scenarios is Nexus suspending the interface, which is covered in LACP Suspended interface section.

Verify LACP Suspended interface

sh port-channel summary interface port-channel 1

Flags:  D - Down        P - Up in port-channel (members)
        I - Individual  H - Hot-standby (LACP only)
        s - Suspended   r - Module-removed
        b - BFD Session Wait
        S - Switched    R - Routed
        U - Up (port-channel)
        p - Up in delay-lacp mode (member)
        M - Not in use. Min-links not met
--------------------------------------------------------------------------------
Group Port-       Type     Protocol  Member Ports
      Channel
--------------------------------------------------------------------------------
1     Po1(SD)     Eth      LACP      Eth1/1(s) 


sh int e1/1 status
--------------------------------------------------------------------------------
Port         Name           Status     Vlan    Duplex   Speed     Type
--------------------------------------------------------------------------------
Eth1/1       --            suspended   trunk    auto     auto   10Gbase-SR


sh int e1/1
Ethernet1/1 is down (suspended(no LACP PDUs))
admin state is up, Dedicated Interface
  Belongs to Po1
  Hardware: 100/1000/10000/25000 Ethernet, address: 003a.9c08.68ab (bia 003a.9c08.68ab)
  MTU 9216 bytes, BW 10000000 Kbit , DLY 10 usec
  reliability 255/255, txload 1/255, rxload 1/255

  <Snipped>

Note: When facing this scenario Nexus is not receiving LACP PDUS from partner, LACP interfaces counters can be verified, as written section: Verify LACP interface counters or packet captures such as SPAN or ELAM (Described on section LACP ELAM) can be taken.

Verify LACP interface counters

Each device must send and receive LACPDUs at the same rate in order for the port-channel to come up.

N9K1 N9K2

sh lacp counters interface port-channel 1
NOTE: Clear lacp counters to get accurate statistics
------------------------------------------------------------------------------
                             LACPDUs                      Markers/Resp LACPDUs
Port              Sent                Recv                  Recv Sent  Pkts Err
------------------------------------------------------------------------------
port-channel1
Ethernet1/1        445                  445                    0      0    0   
Ethernet1/2        445                  445                    0      0    0

sh lacp counters interface port-channel 1
NOTE: Clear lacp counters to get accurate statistics
------------------------------------------------------------------------------
                             LACPDUs                      Markers/Resp LACPDUs
Port              Sent                Recv                  Recv Sent  Pkts Err
------------------------------------------------------------------------------
port-channel1
Ethernet1/1        445                  445                    0      0    0   
Ethernet1/2        445                  445                    0      0    0

Verify LACP Actor State Bits

In each LACP PDU Actor state information is exchanged between Partner and Actor.

Activity	1: Active mode	0: Passive mode
Timeout	1: Short timeout	0: Long Timeout
Aggregation	1: Aggregatable	0: Individual
Sync	1: In Sync	0: Out of Sync
Collecting	1: Collecting Enabled	0: Collecting Disabled
Distributing	1: Distributing Enabled	0: Distributing Disabled
Defaulted	1: Use default for partner	0: Use rx LACPDU for partner
Expired	1: Partner PDU Expired	0: Not Expired

Note: Table 2.0 Actor State Bits meaning

Verify LACP State Hexadecimal Value:

user interface

Note: Image 3.0 LACP state conversion from binary to Hexadecimal

Verify LAG ID

Link Agregation Identifier is the information that each physical interface member of the same port-channel are sharing, to appear as a single "virtual interface" . It can be verified using commands.

N9K1 LAG ID

N9K2 LAG ID

sh lacp interface e1/1 | include iignore  local|lag
Lag Id: [ [(1770, a8-c-d-96-43-7f, 5, 8000, 1c9), (1770, a8-c-d-96-c9-bf, 5, 8000, 1c9)] ]
Local Port: Eth1/1 MAC Address=a8-c-d-96-c9-bf


sh lacp interface e1/2 | include iignore  local|lag
Lag Id: [ [(1770, a8-c-d-96-43-7f, 5, 8000, 1ca), (1770, a8-c-d-96-c9-bf, 5, 8000, 1ca)] ]
Local Port: Eth1/2 MAC Address=a8-c-d-96-c9-bf

sh lacp interface e1/1 | include iignore  local|lag
Lag Id: [ [(1770, a8-c-d-96-c9-bf, 5, 8000, 1c9),(1770, a8-c-d-96-43-7f, 5, 8000, 1c9)] ]
Local Port: Eth1/1 MAC Address=a8-c-d-96-43-7f


sh lacp interface e1/2 | include iignore  local|lag
Lag Id: [ [(1770, a8-c-d-96-c9-bf, 5, 8000, 1c9),(1770, a8-c-d-96-43-7f, 5, 8000, 1c9)] ]
Local Port: Eth1/2 MAC Address=a8-c-d-96-43-7f

Verify LACP PDU Exchange

There are certain scenarios where even if Nexus is exchanging LACP PDUs at correct rate, port-channel does not come up.

This could be due a failure on LACP negotiation.

An example of a correct LACP transaction for a port-channel to come up is showed in this table.

1	N9K1 Actor	N9K2 Partner
N9K1 send LACP with actor information with the state bits. Partner information is at 0s since N9K1 has not received any LACP PDU from partner.
2	N9K1 Partner	N9K2 Actor
N9K2 receive information fron N9K1. N9K2 send LACP PDU with its information and acknowledge of N9K1 information .
3	N9K1 Actor	N9K2 Partner
N9K1 Acknowledge N9K2 information.
4	N9K1 Partner	N9K2 Actor
N9K2 receives acknowledgre from N9K1. N9K2 sends LACP PDU adding SYNC bit at 1.
5	N9K1 Actor	N9K2 Partner
N9K1 acknowledge SYNC bit from N9K2. N9K1 adds SYNC bit at 1 to LACP PDU.
6	N9K1 Partner	N9K2 Actor
N9K2 Acknoledge SYNC bit from N9K1. N9K2 adds Collect bit at 1 to LACP PDU.
7	N9K1 Actor	N9K2 Partner
N9K1 Acknowledge Collect bit from N9K2. N9K1 Adds Collect bit to its LACP PDU.
8	N9K1 Actor	N9K2 Partner
N9K1 decides that is ready to transition to distribute state, so it changes now Time Out bit from 1 (fast) to 0 (Slow) and sets Distribute bit to 1.
9	N9K1 Partner	N9K2 Actor
N9k2 acknowledge N9k1 PDU and changes its Time Out bit from 1 to 0 and sets distribute bite to 1. At this moment both nexus are ready to send data on the port-channel.
10	N9K1 Actor	N9K2 Partner
N9K1 Acknowledge LACP PDU from N9K2. At this moment Port-Channel woll transition to up.

Verify LACP FSM log

LACP Finite State Machine has a dedicated logg where it stores all the events of the interface LACP states and LACP PDUS can be found on this log:

sh lacp internal info interface e1/1 detail fsmlog

On new versions you can also use:

sh lacp internal event-history interface e1/1
First section describes interface LACP transitions

>>>>FSM: <Ethernet1/1> has 61 logged transitions<<<<<
<Snipped>

58) FSM:<Ethernet1/1> Transition at 127198 usecs after Mon Aug 14 22:34:42 2023
    Previous state: [LACP_ST_WAIT_FOR_HW_TO_PROGRAM_RECEIVE_PATH]
    Triggered event: [LACP_EV_PORT_RECEIVE_PATH_ENABLED_AS_CHANNEL_MEMBER_MESSAGE]
    Next state: [LACP_ST_PORT_MEMBER_RECEIVE_ENABLED]

59) FSM:<Ethernet1/1> Transition at 127227 usecs after Mon Aug 14 22:34:42 2023
    Previous state: [LACP_ST_PORT_MEMBER_RECEIVE_ENABLED]
    Triggered event: [LACP_EV_PARTNER_PDU_IN_SYNC_COLLECT_ENABLED_DISTRIBUTING_DISABLED]
    Next state: [LACP_ST_WAIT_FOR_HW_TO_PROGRAM_TRANSMIT_PATH]

60) FSM:<Ethernet1/1> Transition at 128265 usecs after Mon Aug 14 22:34:42 2023
    Previous state: [LACP_ST_WAIT_FOR_HW_TO_PROGRAM_TRANSMIT_PATH]
    Triggered event: [LACP_EV_PERIODIC_TRANSMIT_TIMER_EXPIRED]
    Next state: [FSM_ST_NO_CHANGE]

61) FSM:<Ethernet1/1> Transition at 134352 usecs after Mon Aug 14 22:34:42 2023
    Previous state: [LACP_ST_WAIT_FOR_HW_TO_PROGRAM_TRANSMIT_PATH]
    Triggered event: [LACP_EV_PORT_HW_PATH_ENABLED]
    Next state: [LACP_ST_PORT_MEMBER_COLLECTING_AND_DISTRIBUTING_ENABLED]
    Curr state: [LACP_ST_PORT_MEMBER_COLLECTING_AND_DISTRIBUTING_ENABLED]

Second section shows all the LACP PDUS information that exus has sent or received.

<Snipped>
(1) Send LACP PDU: len:110 at 492243 usecs after Tue Aug 15 00:02:13 2023
01010114 8000f8a7 3a393d6b 80008000 01013d00 00000214 8000f8a7 3a2ea30f
80008000 01013d00 00000310 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 0000
Actor:
    info: (8000, f8-a7-3a-39-3d-6b, 8000, 8000, 101)
    state:0x0f (Ac-1:To-1:Ag-1:Sy-1:Co-0:Di-0:De-0:Ex-0)
Partner:
    info: (8000, f8-a7-3a-2e-a3-f, 8000, 8000, 101)
    state:0x0f (Ac-1:To-1:Ag-1:Sy-1:Co-0:Di-0:De-0:Ex-0

(2) Recv LACP PDU: len:124 at 708749 usecs after Tue Aug 15 00:02:12 2023
0180c200 0002f8a7 3a2ea310 88090101 01148000 f8a73a2e a30f8000 80000101
3d000000 02148000 f8a73a39 3d6b8000 80000101 3d000000 03100000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
Actor:
    info: (8000, f8-a7-3a-2e-a3-f, 8000, 8000, 101)
    state:0x0f (Ac-1:To-1:Ag-1:Sy-1:Co-0:Di-0:De-0:Ex-0)
Partner:
    info: (8000, f8-a7-3a-39-3d-6b, 8000, 8000, 101)
    state:0x07 (Ac-1:To-1:Ag-1:Sy-0:Co-0:Di-0:De-0:Ex-0)

Note: Please take in consideration that LACP PDU event history time line goes from newer logs to older logs however LACP states event-history time line goes from older logs to newer logs.

Configure and verify LACP Ethanalyzer

LACP PDUS needs to be proceced by CPU , nexus has installed in hardware internal access list to redirect LACP packets to CPU, all LACP PDUS can be observed with ethanalyzer, in order to filter them wireshark filter "slow" can be used.

ethanalyzer local interface inband display-filter "slow and eth.addr==04:76:b0:b2:00:20 and eth.addr==01:80:c2:00:00:02" limit-captured-frames 0
Capturing on inband
2023-07-03 23:37:14.420839 04:76:b0:b2:00:20 -> 01:80:c2:00:00:02 LACP Link Aggregation Control ProtocolVersion 1. Actor Port = 257 Partner Port = 449  

Detailed:


Frame 19 (124 bytes on wire, 124 bytes captured)
    Arrival Time: Jul 3, 2023 23:38:14.425502000
    [Time delta from previous captured frame: 0.836575000 seconds]
    [Time delta from previous displayed frame: 11.246799000 seconds]
    [Time since reference or first frame: 11.246799000 seconds]
    Frame Number: 19
    Frame Length: 124 bytes
    Capture Length: 124 bytes
    [Frame is marked: False]
    [Protocols in frame: eth:slow]
Ethernet II, Src: 04:76:b0:b2:00:20 (04:76:b0:b2:00:20), Dst: 01:80:c2:00:00:02 (01:80:c2:00:00:02)
    Destination: 01:80:c2:00:00:02 (01:80:c2:00:00:02)
        Address: 01:80:c2:00:00:02 (01:80:c2:00:00:02)
        .... ...1 .... .... .... .... = IG bit: Group address (multicast/broadcast)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
    Source: 04:76:b0:b2:00:20 (04:76:b0:b2:00:20)
        Address: 04:76:b0:b2:00:20 (04:76:b0:b2:00:20)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)

    Type: Slow Protocols (0x8809)
Link Aggregation Control Protocol
    Slow Protocols subtype: LACP (0x01)
    LACP Version Number: 0x01
    Actor Information: 0x01
    Actor Information Length: 0x14
    Actor System Priority: 32768
    Actor System: 04:76:b0:b2:00:1f (04:76:b0:b2:00:1f)
    Actor Key: 32768
    Actor Port Priority: 32768
    Actor Port: 257
    Actor State: 0x3d (Activity, Aggregation, Synchronization, Collecting, Distributing)
        .... ...1 = LACP Activity: Yes
        .... ..0. = LACP Timeout: No
        .... .1.. = Aggregation: Yes
        .... 1... = Synchronization: Yes
        ...1 .... = Collecting: Yes
        ..1. .... = Distributing: Yes
        .0.. .... = Defaulted: No
        0... .... = Expired: No
    Reserved: 000000
    Partner Information: 0x02
    Partner Information Length: 0x14
    Partner System Priority: 32768
    Partner System: 70:0f:6a:d7:d0:fb (70:0f:6a:d7:d0:fb)
    Partner Key: 32768
    Partner Port Priority: 32768
    Partner Port: 449
    Partner State: 0x3d (Activity, Aggregation, Synchronization, Collecting, Distributing)
        .... ...1 = LACP Activity: Yes
        .... ..0. = LACP Timeout: No
        .... .1.. = Aggregation: Yes
        .... 1... = Synchronization: Yes
        ...1 .... = Collecting: Yes
        ..1. .... = Distributing: Yes
        .0.. .... = Defaulted: No
        0... .... = Expired: No
    Reserved: 000000
    Collector Information: 0x03
    Collector Information Length: 0x10
    Collector Max Delay: 0
    Reserved: 000000000000000000000000
    Terminator Information: 0x00
    Terminator Length: 0x00
    Reserved: 000000000000000000000000000000000000000000000000...

Configure and verify LACP Elam

First mac address from remote interface needs to be identified:

N9K2#sh int e1/1 | i i addr
Hardware: 1000/10000/25000/40000/50000/100000 Ethernet, address: 0476.b0b2.0020 (bia 0476.b0b2.0020)

Now on nexus N9K1 elam is configured.

N9K1#debug platform internal tah elam 
N9K1(TAH-elam)#trigger init 
N9K1(TAH-elam-insel6)#set outer l2 src_mac 04:76:b0:b2:00:20 dst_mac 01:80:c2:00:00:02 <<<<<Dest mac is mcast mac for LACP
N9K1(TAH-elam-insel6)#tart
N9K1(TAH-elam-insel6)#report
SUGARBOWL ELAM REPORT SUMMARY
slot - 1, asic - 0, slice - 1
============================Incoming Interface: Eth1/49
Src Idx : 0x601, Src BD : 1
Outgoing Interface Info: met_ptr 0Packet Type: CE

Dst MAC address: 01:80:C2:00:00:02
Src MAC address: 04:76:B0:B2:00:20
Sup hit: 1, Sup Idx: 2627. <<<<<Traffic needs to be punted to the CPU.
Drop Info:
----------LUA:
LUB:
LUC:
LUD:
Final Drops:vntag:
vntag_valid : 0
vntag_vir : 0
vntag_svif : 0

In order to decode the sup redirect index, comand sh system internal access-list sup-redirect-stats can be excecuted:

sh system internal access-list sup-redirect-stats | i i 2627
2627 LACP 0
2627 LACP 103

Revision History

Revision	Publish Date	Comments
1.0	05-Oct-2023	Initial Release

Contributed by Cisco Engineers

Juan Carlos Gandaria Alonso
Escalation Engineer

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Troubleshoot Link Aggregation Control Protocol (LACP) on Nexus

Available Languages

Download Options

Bias-Free Language

Contents

Introduction

Prerequisites

Requirements

Components Used

Topology

Verify LACP Link Status

Configure LACP:

Verify port-channel status

Verify LACP Suspended interface

Verify LACP interface counters

Verify LACP Actor State Bits

Verify LACP State Hexadecimal Value:

Verify LAG ID

Verify LACP PDU Exchange

Verify LACP FSM log

Configure and verify LACP Ethanalyzer

Configure and verify LACP Elam

Revision History

Contributed by Cisco Engineers

Was this Document Helpful?

Contact Cisco