Configuring LACP (802.3ad) Between a Catalyst 6500/6000 and a Catalyst 4500/4000

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Updated:December 14, 2005
Document ID:19642

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Introduction

This document will show the basic configuration needed to set up an 802.3ad link aggregate between a Catalyst 6500/6000 (running Catalyst OS [CatOS] system software) and a Catalyst 4500/4000 switch. 802.3ad is a new specification from the IEEE that allows us to bundle several physical ports together to form one logical port. This is very similar to the already existing Cisco EtherChannel Solution. The main difference is that the Cisco implementation uses a proprietary protocol called Port Aggregation Protocol (PAgP). The IEEE later defined within 802.3ad a new control protocol for link aggregation called Link Aggregate Control Protocol (LACP).

The primary advantage of using LACP (802.3ad) is for interoperability with other vendor switches. Since PAgP is Cisco proprietary, one cannot aggregate channels between a Cisco switch and a switch from another vendor unless LACP is utilized.

For more details on configuring LACP using CatOS, refer to the following documents:

For information on how to configure LACP using Cisco IOS® Software, refer to the following documents:

Before You Begin

Conventions

For more information on document conventions, see the Cisco Technical Tips Conventions.

Prerequisites

Before attempting this configuration, please ensure that you meet the prerequisites below.

LACP can be used with the following platforms and versions:

  • Catalyst 6500/6000 series with CatOS version 7.1(1) and later

  • Catalyst 6500/6000 series with Cisco IOS Software Release 12.1(11b)EX and later

  • Catalyst 4500/4000 series with CatOS version 7.1(1) and later

  • Catalyst 4500/4000 Series with Cisco IOS Software Release 12.1(13)EW and later

Components Used

The information in this document is based on the software and hardware versions below.

  • Catalyst 4003 switch running CatOS 7.1(1) software

  • Catalyst 6500 switch running CatOS 7.1(1) software

  • Catalyst 6500 switch running Cisco IOS Software Release 12.1(13)E9

Background Theory

LACP trunking supports four modes of operation, as follows:

  • On: The link aggregation is forced to be formed without any LACP negotiation .In other words, the switch will neither send the LACP packet nor process any incoming LACP packet. This is similar to the on state for PAgP.

  • Off: The link aggregation will not be formed. We do not send or understand the LACP packet. This is similar to the off state for PAgP.

  • Passive: The switch does not initiate the channel, but does understand incoming LACP packets. The peer (in active state) initiates negotiation (by sending out an LACP packet) which we receive and reply to, eventually forming the aggregation channel with the peer. This is similar to the auto mode in PAgP.

  • Active: We are willing to form an aggregate link, and initiate the negotiation. The link aggregate will be formed if the other end is running in LACP active or passive mode. This is similar to the desirable mode of PAgP.

There are only three valid combinations to run the LACP link aggregate, as follows:

Switch Switch Comments
active active Recommended.
active passive Link aggregation occurs if negotiation is successful.
on on Link aggregation occurs without LACP. Although this works, it is not recommended.

Note: By default, when an LACP channel is configured, the LACP channel mode is passive.

Difference Between CatOS and Cisco IOS System Software

CatOS on the Supervisor Engine and Cisco IOS Software on the MSFC (Hybrid): a CatOS image can be used as the system software to run the Supervisor Engine on Catalyst 6500/6000 switches. If the optional Multilayer Switch Feature Card (MSFC) is installed, a separate Cisco IOS Software image is used to run the MSFC.

Cisco IOS Software on both the Supervisor Engine and MSFC (Native): a single Cisco IOS Software image can be used as the system software to run both the Supervisor Engine and MSFC on Catalyst 6500/6000 switches.

Note: For more information, refer to Comparison of the Cisco Catalyst and Cisco IOS Operating Systems for the Cisco Catalyst 6500 Series Switch.

Configure

We assume that we are starting with switches containing empty configurations, and thus having all parameters set as default. We will now include the commands necessary to configure LACP. The steps include the Cisco IOS Software and CatOS commands required. Pick the appropriate command depending on the software that is running on the switch.

Step 1: Setting the channel protocol to LACP

CatOS

By default, all ports on a Catalyst 4500/4000 and a Catalyst 6500/6000 use channel protocol PAgP and as such are not running LACP. For all ports concerned, you then need to change the channel mode to LACP. On switches running CatOS, you can only change channel mode per module. In the following example, we will change the channel mode for slot 1 and 2 using the set channelprotocol lacp module_number command.  The changes can be verified by using the show channelprotocol command.

CatOSSwitch (enable) set channelprotocol lacp 1
        Mod 1 is set to LACP protocol.
        CatOSSwitch (enable) set channelprotocol lacp 2
        Mod 2 is set to LACP protocol.

        CatOSSwitch (enable) show channelprotocol
                         Channel
        Module  Protocol
        ------- --------
        1           LACP
        2           LACP
        3           PAGP
        5           PAGP

Cisco IOS Software

The ports on a Catalyst 6500/6000 or a Catalyst 4500/4000 running Cisco IOS Software can act as L2 switchports or L3 routed ports depending on the configuration. For this scenario, configure the interface as a L2 switchport by issuing the switchport command in interface configuration mode. 

CiscoIOSSwitch(config)#interface gigabitEthernet 1/1
CiscoIOSSwitch(config-if)#switchport

Next specify which interfaces should be using LACP using the command channel-protocol lacp.

CiscoIOSSwitch(config-if)#channel-protocol lacp

Step 2: Assigning the same admin key to each port that will form the channel and settings channel mode

CatOS

There is a parameter exchanged in the LACP packet called the admin key. A channel will only be formed between ports having the same admin key. By issuing the set port lacp-channel mod/ports_list command, you will assign all ports in the port_list the same admin key.

For example, on one device, we assign both ports to the same group. (It gets randomly assigned admin key 56.) 

CatOSSwitch (enable) set port lacp-channel 1/1,2/1
        Port(s) 1/1,2/1 are assigned to admin key 56

On the other device, we also assign the ports to a single key. (It gets randomly assigned admin key 73.) 

OtherCatOSSwitch> (enable) set port lacp-channel 3/33-34
        Port(s) 3/33-34 are assigned to admin key 73

Keep in mind that the admin key is only locally significant. In other words, it must be the same only for ports within the switch and is not a factor between different switches.

Cisco IOS Software

If your device runs Cisco IOS Software, this step can be avoided. Proceed directly to Step 3.

Step 3: Change the LACP channel mode

CatOS

The last step to form the channel is to change the LACP channel mode to active state on one or both of the sides. This can be done using the same commands as those used in Step 2, however, now specifying mode active state. The command syntax is as follows:

set port lacp-channel mod/ports_list mode {on | off | active | passive}

For example:

CatOSSwitch (enable) set port lacp-channel 1/1,2/1 mode active
        Port(s) 1/1,2/1 channel mode set to active.

Note: To find additional information on the commands used in this document, use the Command Lookup Tool (registered customers only) .

Cisco IOS Software

When you are configuring LACP on a Catalyst 6500/6000 running Cisco IOS Software, use the channel-group command to assign interfaces to the same group. 

channel-group number mode {active | on | passive}

Note: PAgP mode options like 'auto' and 'desirable' are available for this command as well, but will not be discussed since this document pertains to configuring LACP only.

Note: The number of valid values for the channel-group number depends on the software release. For releases earlier than Cisco IOS Software Release 12.1(3a)E3, valid values are from 1 to 256; for Cisco IOS Software Releases 12.1(3a)E3, 12.1(3a)E4, and 12.1(4)E1, valid values are from 1 to 64. Cisco IOS Software Release 12.1(5c)EX and later support a maximum of 64 values ranging from 1 to 256.

The configuration on 6500/6000 running Cisco IOS Software will be:

CiscoIOSSwitch(config)#interface gigabitEthernet 1/1
CiscoIOSSwitch(config-if)#channel-group 1 mode active 
Creating a port-channel interface Port-channel 1
CiscoIOSSwitch(config-if)#interface gigabitEthernet 2/1
CiscoIOSSwitch(config-if)#channel-group 1 mode active
Creating a port-channel interface Port-channel 1

Note: To find additional information on the commands used in this document, use the Command Lookup Tool (registered customers only) .

Network Diagram

This document uses the network setup shown in the diagram below.

126-a.gif

In this example, we configure an LACP aggregate link between a Catalyst 4000 and Catalyst 6000 series switch using two Gigabit Ethernet ports as shown in the diagram above.

Note: In this example, the Catalyst 6000 is running Cisco IOS Software and the Catalyst 4000 is running CatOS. However, it is important to remember that the Cisco IOS LACP configuration can be used on any Catalyst 4500/4000 or 6500/6000 switch running Cisco IOS Software. Moreover, the CatOS configuration included below can also be applied to any Catalyst 4500/4000 or 6500/6000 switch running CatOS as well.

Configurations

The information presented in this document was created from devices in a specific lab environment. The configurations on all devices were cleared with the clear config all command (for CatOS) and the write erase command (for Cisco IOS Software) to ensure that they had a default configuration. If you are working in a live network, ensure that you understand the potential impact of any command before using it.

buran (Catalyst 4000) 
begin 
# ***** NON-DEFAULT CONFIGURATION ***** 
! 
#time: Thu Jan 17 2002, 17:54:23 
! 
#version 7.1(1) 
! 
#system web interface version(s) 
! 
#system 
set system name  buran 
! 

!--- Output suppressed.

! 
#channelprotocol 
set channelprotocol lacp 3 

!--- All ports in module 3 are in LACP channel mode. 

! 
#port channel 
set port lacp-channel 3/33-34 73 

!--- Ports 3/33 and 3/34 have a single admin key (73). !--- Since we have not explicitly specified the LACP channel mode, !--- the ports are in passive mode. However to prevent LACP negotiation !--- problems, Cisco recommends that you configure LACP active mode using the !--- set port lacp-channel 3/33-34 mode active command.

! 
#multicast filter 
set igmp filter disable 
! 
#module 1 : 0-port Switching Supervisor 
! 
#module 2 : 48-port 10/100BaseTx Ethernet 
set port disable    2/48 
! 
#module 3 : 34-port 10/100/1000 Ethernet 
end

nelix (Catalyst 6000) using Cisco IOS Software 
 
version 12.1
!
hostname nelix
!
ip subnet-zero
!

!--- Output suppressed.

!
interface Port-channel1 

!--- Cisco IOS Software automatically creates this logical interface when the !--- channel-group command is used under the physical interface.

 
no ip address
switchport 
!
interface GigabitEthernet1/1
no ip address
switchport 

!--- This sets the LAN interface as a Layer 2 interface.

channel-group 1 mode active

!--- Port 1/1 is part of channel-group 1 using LACP in Active mode.

!
interface GigabitEthernet1/2
no ip address
shutdown

!--- This interface is unused.

!
interface GigabitEthernet2/1
no ip address
switchport  

!--- This sets the LAN interface as a Layer 2 interface.

channel-group 1 mode active

!--- Port 2/1 is part of channel-group 1 using LACP in Active mode.

Verify

This section provides information that can be used to verify your configuration

Note: Some of the outputs shown below were not captured from the above scenario. The intent of this section is to explain how to verify that your configuration is correct. This includes showing outputs from similar scenarios to provide a more complete explanation.

Certain show commands are supported by the Output Interpreter Tool (registered customers only) , which allows you to view an analysis of show command output.

Note: To find additional information on the commands used in this document, use the Command Lookup Tool (registered customers only) .

CatOS

This section includes show commands for switches running CatOS.

  • show port lacp-channel—Displays information about LACP channels by port or module number. If you do not enter a module or a port number, information about all modules is displayed. If you enter the module number only, information about all ports on the module is displayed. Verify that the desired ports appear and the ports that are supposed to be in a channel have the same Admin Key and desired channel mode.

  • show lacp-channel mac—Displays MAC information about the LACP channel. Verify that the channel is transmitting and receiving traffic by running the command multiple times and verifying that the counters increment.

You can first verify that the port is effectively channeling using the show port lacp-channel command on both switches. The following output is shown as an example of a switch running CatOS and in LACP passive mode (as configured above):

CatOSSwitch (enable) show port lacp-channel 
Port   Admin Channel LACP Port  Ch   Partner Oper                    Partner 
       key   Mode    Priority   id   Sys ID                          Port 
------ ----- ------- --------- ---- -------------------------------- ------- 
 3/33    73  passive    128     849  32768:00-50-0f-2d-40-00           65 
 3/34    73  passive    128     849  32768:00-50-0f-2d-40-00            1

The following output shows an example of a peer switch running CatOS and in LACP active mode. (This was not configured above.) 

CatOSSwitch (enable) show port lacp-channel
Port   Admin Channel LACP Port  Ch   Partner Oper                    Partner 
       key   Mode    Priority   id   Sys ID                          Port 
------ ----- ------- --------- ---- -------------------------------- ------- 
 1/1     56  active     128     769  32768:00-01-42-29-25-00          162 
 2/1     56  active     128     769  32768:00-01-42-29-25-00          161 

Note: Notice that LACP channels on one switch are in active mode while those on the other are in passive mode. If both switches were set to active, that would be indicated in the above output.

You can also verify that the channel is transmitting and receiving traffic by viewing the show lacp-channel mac command output for the channel ID corresponding to your channel. (See channel ID in the above command output.) The counters here should increase over time. 

CatOSSwitch (enable) show lacp-channel mac 
Channel  Rcv-Unicast          Rcv-Multicast        Rcv-Broadcast 
-------- -------------------- -------------------- -------------------- 
769                       143                65846                   33 
Channel  Xmit-Unicast         Xmit-Multicast       Xmit-Broadcast 
-------- -------------------- -------------------- -------------------- 
769                       159                20763                  123 

Channel  Rcv-Octet            Xmit-Octet 
-------- -------------------- -------------------- 
769                   5427372              2486321 

Channel  Dely-Exced MTU-Exced  In-Discard Lrn-Discrd In-Lost    Out-Lost 
-------- ---------- ---------- ---------- ---------- ---------- ---------- 
769               0          0          0          0          0          0

You can also verify, from the output below, that the two ports are now one unique port from the Spanning Tree Protocol (STP) point of view. 

CatOSSwitch (enable) show spantree 1 active 
VLAN 1 
Spanning tree mode          PVST+ 
Spanning tree type          ieee 
Spanning tree enabled 
Designated Root             00-01-42-29-25-00 
Designated Root Priority    32768 
Designated Root Cost        3 
Designated Root Port        1/1,2/1 (agPort 13/1) 
Root Max Age   20 sec   Hello Time 2  sec   Forward Delay 15 sec 

Bridge ID MAC ADDR          00-50-0f-2d-40-00 
Bridge ID Priority          32768 
Bridge Max Age 20 sec   Hello Time 2  sec   Forward Delay 15 sec 

Port                     Vlan Port-State    Cost      Prio Portfast Channel_id 
------------------------ ---- ------------- --------- ---- -------- ---------- 
1/1,2/1                  1    forwarding            3   32 disabled 769
 3/1                     1    blocking             19   32 disabled 0 
 3/2                     1    blocking             19   32 disabled 0 
 3/3                     1    blocking             19   32 disabled 0

Cisco IOS Software

The following commands can be used on switches running Cisco IOS Software:

  • show etherchannel port-channel—Displays LACP port channel information, similar to the information provided by the show port lacp-channel command in CatOS. Details about the status of the channel, the protocol being used, and the time since the ports were bundled for all the channel groups configured are also displayed. 

    CiscoIOSSwitch#show etherchannel port-channel             
                    Channel-group listing:             
                    -----------------------
Group: 1
----------
              Port-channels in the group:
              ----------------------
Port-channel: Po1 (Primary Aggregator)
------------
Age of the Port-channel =    00d:00h:16m:01s
Logical slot/port    = 14/1 Number of ports = 2
Port state           = Port-channel Ag-Inuse
Protocol             = LACP
Ports in the Port-channel:
Index   Load   Port   EC state
------+------+------+------------
  0      55    Gi1/1   Active
  1      AA    Gi2/1   Active
Time since last port bundled: 00d:00h:15m:28s Gi2/1
nelix#

    From the output shown on nelix above, we see that the protocol being used here is LACP, and the two gigabit ports 1/1 and 2/1 were bundled together to form the etherchannel for Port-channel 1. The channel has been in the active state for the last 15 minutes.

  • show etherchannel channelgroup_number detail—Displays detailed information for the channel group specified with the details of each port shown separately. It includes information about the partner details and the port channel details. 

    CiscoIOSSwitch#show etherchannel 1 detail
Group state = L2
Ports: 2   Maxports = 16
Port-channels: 1 Max Port-channels = 16
Protocol:   LACP
Ports in the group: 
-------------------
Port: Gi1/1
------------

Port state    = Up Mstr In-Bndl
Channel group = 1       Mode = Active          Gcchange = -
Port-channel  = Po1       GC = - Pseudo    port-channel = Po1
Port index    = 0       Load = 0x55            Protocol = LACP
Flags: S - Device is sending Slow LACPDUs F - Device is sending fast LACPDUs.
       A - Device is in active mode. P - Device is in passive mode.
Local information:
                       LACP port  Admin   Oper  Port     Port
Port    Flags  State   Priority   Key     Key   Number   State
Gi1/1    SA    bndl    32768      0x1     0x1   0x101    0x3D
Partner's information:
        Partner              Partner            Partner
Port    System ID            Port Number   Age  Flags
Gi1/1   32768,0009.7c0f.9800 0x82          11s  SP
        LACP Partner   Partner    Partner
        Port Priority  Oper Key   Port State
        128            0x102      0x3C
Age of the port in the current state: 00d:00h:19m:56s
Port: Gi2/1
------------
Port state = Up Mstr In-Bndl
       Channel group = 1     Mode = Active      Gcchange     = -
       Port-channel  = Po1   GC   = - Pseudo    port-channel = Po1
       Port index    = 1     Load = 0xAA        Protocol     = LACP
Flags: S - Device is sending Slow LACPDUs F - Device is sending fast LACPDUs.
       A - Device is in active mode. P - Device is in passive mode.
Local information:
                     LACP port   Admin   Oper  Port     Port
Port   Flags  State  Priority    Key     Key   Number   State
Gi2/1  SA     bndl   32768       0x1     0x1   0x201    0x3D
Partner's information:
       Partner               Partner           Partner
Port   System ID             Port Number  Age  Flags
Gi2/1  32768,0009.7c0f.9800  0x81         14s  SP
       LACP Partner     Partner    Partner
       Port Priority    Oper Key   Port State
       128              0x102      0x3C
Age of the port in the current state: 00d:00h:19m:27s
 Port-channels in the group:
 ----------------------
Port-channel: Po1 (Primary Aggregator)
------------
Age of the Port-channel = 00d:00h:20m:01s
         Logical slot/port = 14/1 Number of ports = 2
         Port state        = Port-channel Ag-Inuse
         Protocol          = LACP
Ports in the Port-channel:
Index   Load   Port   EC state
------+------+------+------------
  0     55    Gi1/1   Active
  1     AA    Gi2/1   Active
Time since last port bundled: 00d:00h:19m:28s Gi2/1

    You can also verify from the outputs below that both ports Gi 1/1 and Gi 2/1 are in a forwarding state since the two ports are now one unique port from the STP point of view. 

    CiscoIOSSwitch#show spanning-tree vlan 1 interface gigabitEthernet 1/1   
      Vlan       Role Sts   Cost    Prio.Nbr            Type
---------------- ---- --- --------- -------- --------------------------------
  VLAN0001       Root FWD     3     128.833             P2p
nelix#show spanning-tree vlan 1 interface gigabitEthernet 2/1
      Vlan       Role Sts   Cost    Prio.Nbr             Type
---------------- ---- --- --------- -------- --------------------------------
  VLAN0001       Root FWD     3     128.833              P2p      

CiscoIOSSwitch#show spanning-tree vlan 1 active
VLAN0001
     Spanning tree enabled protocol ieee
     Root ID Priority 32768
             Address 0009.7c0f.9800
             Cost 3
             Port 833 (Port-channel1)
             Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
 Bridge ID Priority 32768
           Address 0009.e919.9481
           Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
           Aging Time 300
       Interface      Role Sts   Cost    Prio.Nbr             Type
     ---------------- ---- --- --------- -------- --------------------------------
          Po1         Root FWD     3     128.833               P2p

Troubleshoot

Secondary Aggregator Ports Po1A or Po2A are Created

A secondary aggregator port will be created in the LACP process when the ports you are bundling are not compatible with each other, or with their remote peers. The secondary aggregator port will have the ports which are compatible with others.

Switch#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
Number of channel-groups in use: 6
Number of aggregators:           8

Group  Port-channel  Protocol    Ports
------+-------------+-----------+-----------------------------------------
1      Po1(SU)         LACP      Gi1/16(P)  Gi10/1(P)  Gi10/2(P)
2      Po2(SD)         LACP
2      Po2A(SU)        LACP      Gi1/15(P)  Gi10/3(P)  Gi10/4(P)
3      Po3(SU)         LACP      Gi1/14(P)  Gi10/5(P)  Gi10/6(P)
4      Po4(SD)         LACP
4      Po4A(SU)        LACP      Gi1/13(P)  Gi10/7(P)  Gi10/8(P)
5      Po5(SU)         LACP      Gi1/12(P)  Gi10/9(P)  Gi10/10(P)
6      Po6(SU)         LACP      Gi1/11(P)  Gi10/11(P) Gi10/12(P)

Configure all LAN ports in an EtherChannel to operate at the same speed and in the same duplex mode. LACP does not support half-duplex. Half-duplex ports in an LACP EtherChannel are put in the suspended state.

If you configure an EtherChannel from trunking LAN ports, verify that the trunking mode is the same on all the trunks. LAN ports in an EtherChannel with different trunk modes can operate unpredictably.

LAN ports with different STP port path costs can form an EtherChannel as long they are compatibly configured with each other. If you set different STP port path costs, the LAN ports are not incompatible for the formation of an EtherChannel.

For a more comprehensive list, refer to the EtherChannel Feature Configuration Guidelines and Restrictions section of Configuring EtherChannels.

Related Information

Revision History

Revision Publish Date Comments
1.0
15-Feb-2002
Initial Release

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