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  1. Link Aggregation Concepts
  2. Link Aggregation Configuration
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This chapter is from the book

Link Aggregation Configuration

EtherChannel configuration is rather straightforward once you decide on which protocol you will use. In fact, the easiest method is to just force both sides to be on.

Configuring EtherChannel

To configure EtherChannel, complete the following steps:

  • Step 1. Specify the interfaces that, participate in the EtherChannel group using the interface range interface command.

    What are the requirements for each interface before they can form an EtherChannel?

     

  • Step 2. Create the port channel interface with the channel-group identifier mode {on | auto | desirable | active | passive} command in interface range configuration mode. The keyword _______________  forces the port to channel without PAgP or LACP. The keywords _______________  and _______________  enable PAgP. The keywords _______________  and _______________  enable LACP.

  • Step 3. The channel-group command automatically creates a port channel interface using the identifier as the number. Use the interface port-channel identifier command to configure channel-wide settings like trunking, native VLANs, or allowed VLANs.

As you can see from the configuration steps, the way you specify whether to use PAgP, LACP, or no negotiations is by configuring one keyword in the channel-group command.

So, with those steps in mind, consider Figure 3-1 in each of the following configuration scenarios.

Figure 3-1

Figure 3-1 EtherChannel Topology

EtherChannel Configuration Scenario 1

Record the commands, including the switch prompt, to configure the S1 Fa0/1 and Fa0/2 into an EtherChannel without negotiations. Then force the channel to trunking using native VLAN 99.

S1(config)#



EtherChannel Configuration Scenario 1

Record the commands, including the switch prompt, to configure the S1 Fa0/1 and Fa0/2 into an EtherChannel using PAgP. S1 should initiate the negotiations. The channel should trunk, allowing only VLANs 1, 10, and 20.

S1(config)#



EtherChannel Configuration Scenario 1

Record the commands, including the switch prompt, to configure the S1 Fa0/1 and Fa0/2 into an EtherChannel using LACP. S1 should not initiate the negotiations. The channel should trunk, allowing all VLANs.

S1(config)#


Lab - Configuring EtherChannel (SN 3.2.1.4/SwN 5.2.1.4)

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Packet Tracer - Configuring EtherChannel (SN 3.2.1.3/SwN 5.2.1.3)

packet_tracer.jpg

Verifying and Troubleshooting EtherChannel

Record the commands used to display the output in Example 3-1.

Example 3-1 EtherChannel Verification Commands

S1# __________________________________________________________________________________________
Port-channel1 is up, line protocol is up (connected)
  Hardware is EtherChannel, address is 0cd9.96e8.8a01 (bia 0cd9.96e8.8a01)
  MTU 1500 bytes, BW 200000 Kbit/sec, DLY 100 usec,
     reliability 255/255, txload 1/255, rxload 1/255
<output omitted>

S1# __________________________________________________________________________________________
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      f - failed to allocate aggregator

        M - not in use, minimum links not met
        u - unsuitable for bundling
        w - waiting to be aggregated
        d - default port


Number of channel-groups in use: 1
Number of aggregators:           1

Group  Port-channel  Protocol    Ports
------+-------------+-----------+-----------------------------------------------
1      Po1(SU)         LACP      Fa0/1(P)    Fa0/2(P)

S1# __________________________________________________________________________________________
               Channel-group listing:
               ----------------------

Group: 1
----------
               Port-channels in the group:
               ---------------------------

Port-channel: Po1    (Primary Aggregator)

------------

Age of the Port-channel   = 0d:00h:25m:17s
Logical slot/port   = 2/1          Number of ports = 2
HotStandBy port = null
Port state          = Port-channel Ag-Inuse
Protocol            =   LACP
Port security       = Disabled

Ports in the Port-channel:

Index   Load   Port     EC state        No of bits
------+------+------+------------------+-----------
  0     00     Fa0/1    Active             0
  0     00     Fa0/2    Active             0

Time since last port bundled:    0d:00h:05m:41s    Fa0/2
Time since last port Un-bundled: 0d:00h:05m:48s    Fa0/2

S1# __________________________________________________________________________________________
Port state    = Up Mstr Assoc In-Bndl
Channel group = 1           Mode = Active          Gcchange = -
Port-channel  = Po1         GC   =   -             Pseudo port-channel = Po1
Port index    = 0           Load = 0x00            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
Fa0/1     SA      bndl      32768         0x1       0x1     0x102       0x3D

Partner's information:

                  LACP port                        Admin  Oper   Port    Port
Port      Flags   Priority  Dev ID          Age    key    Key    Number  State
Fa0/1     SA      32768     0cd9.96d2.4000   4s    0x0    0x1    0x102   0x3D

Age of the port in the current state: 0d:00h:24m:59s
S1#

When troubleshooting an EtherChannel issue, keep in mind the configuration restrictions for interfaces that participate in the channel. List at least four restrictions.

Refer to the output for S1 and S2 in Example 3-2. Record the command that generated the output.

Example 3-2 Troubleshooting an EtherChannel Issue

S1# __________________________________________________________________________________________
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      f - failed to allocate aggregator
        M - not in use, minimum links not met
        u - unsuitable for bundling
        w - waiting to be aggregated
        d - default port
Number of channel-groups in use: 1
Number of aggregators:           1
Group  Port-channel  Protocol    Ports
------+-------------+-----------+-----------------------------------------------
1      Po1(SD)          -        Fa0/1(D)    Fa0/2(D)
S1# show run | begin interface Port-channel
interface Port-channel1
 switchport mode trunk
!
interface FastEthernet0/1
 switchport mode trunk
 channel-group 1 mode auto
!
interface FastEthernet0/2
 switchport mode trunk
 channel-group 1 mode auto
!
<output omitted>
S 1#
_________________________________________________________________________________
S2# show run | begin interface Port-channel
interface Port-channel1
 switchport mode trunk
!
interface FastEthernet0/1
 switchport mode trunk
 channel-group 1 mode auto
!
interface FastEthernet0/2
 switchport mode trunk
 channel-group 1 mode auto
!
<output omitted>
S2#

Explain why the EtherChannel between S1 and S2 is down.

 

EtherChannel and spanning tree must interoperate. For this reason, the order in which EtherChannel-related commands are entered is important. To correct this issue, you must first remove the port channel. Otherwise, spanning-tree errors cause the associated ports to go into blocking or errdisabled state. With that in mind, what would you suggest to correct the issue shown in Example 3-2 if the requirement is to use PAgP? What commands would be required?

 

Lab - Troubleshooting EtherChannel (SN 3.2.2.4/SwN 5.2.2.4)

note.jpg

Packet Tracer - Troubleshooting EtherChannel (SN 3.2.2.3/SwN 5.2.2.3)

packet_tracer.jpg

Packet Tracer - Skills Integration Challenge (SN 3.3.1.2/SwN 5.3.1.2)

packet_tracer.jpg
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