CCNA Extra Class 07: Concept of EtherChannel & Configuration

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EtherChannel is a Cisco technology that allows you to bundle multiple physical Ethernet interfaces into one logical interface and the bundle of ethernet interfaces is called Port-Channel.

This gives:

  • Higher Bandwidth → adds up the bandwidth of all bundled links.
  • Redundancy & Fault Tolerance → if one link fails, traffic keeps flowing on the others.
  • Load Balancing → distributes traffic across links.
  • Simpler Management → several ports act as one logical interface.

** Channel Groups and Port-Channel Interfaces

A channel group is the configuration command that bundles multiple physical interfaces into one logical EtherChannel and When you assign interfaces to the same channel group, they are automatically associated with a new logical interface called a Port-Channel. 

** EtherChannel Characteristics -

  • Maximum 8 links can be bundled in one EtherChannel.
  • All links in the channel must have:
    • Same speed (e.g., all 1 Gbps).
    • Same duplex mode.
    • Same VLAN information (if on access mode).
    • Same trunking protocol (if trunk mode).
  • Appears as a single logical interface to STP (Spanning Tree Protocol).
  • Load balancing is done based on source/destination IP, MAC, or Layer 4 port numbers.

** Types of EtherChannel in Cisco

  • Static Mode (On)
    • Manually configured, no negotiation.
    • Both sides must be set to on.
  • PAgP (Port Aggregation Protocol) – Cisco proprietary
    • Modes:
      • auto → waits for negotiation.
      • desirable → actively negotiates.
    • Works if one side is desirable and the other is auto or desirable.
  • LACP (Link Aggregation Control Protocol, IEEE 802.3ad standard)
    • Modes:
      • active → actively negotiates.
      • passive → waits for negotiation.
    • Works if one side is active and the other is active or passive.


Objectives - 

Part 1: Configure Basic Switch Settings
Part 2: Configure an EtherChannel with Cisco PAgP 
Part 3: Configure an 802.3ad LACP EtherChannel 
Part 4: Configure a Redundant EtherChannel Link


Part 1: Configure Basic Switch Settings

MultilayerSwitch(config)#vlan 100
MultilayerSwitch(config-vlan)#vlan 99
MultilayerSwitch(config-vlan)#vlan 200

MultilayerSwitch(config)#interface range fastEthernet 0/1-24
MultilayerSwitch(config-if-range)#switchport mode trunk 
MultilayerSwitch(config-if-range)#switchport trunk encapsulation dot1q 
MultilayerSwitch(config-if-range)#switchport mode trunk 
MultilayerSwitch(config-if-range)#switchport trunk allowed vlan 100,200,99

MultilayerSwitch(config)#interface range gigabitEthernet 0/1-2
MultilayerSwitch(config-if-range)#switchport trunk encapsulation dot1q 
MultilayerSwitch(config-if-range)#switchport mode trunk 
MultilayerSwitch(config-if-range)#switchport trunk allowed vlan 99,100,200

MultilayerSwitch#show interfaces | include Ethernet
MultilayerSwitch#show interfaces status 
MultilayerSwitch#show interfaces trunk
MultilayerSwitch#show vlan brief

Part 2: Configure an EtherChannel with Cisco PAgP 

S1(config)#interface range fastEthernet0/21-22
S1(config-if-range)#shutdown 
S1(config-if-range)#channel-group 1 mode desirable 
S1(config-if-range)#no shutdown

S1(config)#interface port-channel 1
S1(config-if)#switchport trunk encapsulation dot1q 
S1(config-if)#switchport mode trunk 

S3(config)#interface range fastEthernet 0/21-22
S3(config-if-range)#channel-group 1 mode desirable 
S3(config-if-range)#no shutdown 

S3(config)#interface port-channel 1 
S3(config-if)#switchport trunk encapsulation dot1q 
S3(config-if)#switchport mode trunk

//Verify the Configuration
S1#show etherchannel summary 
S1#show etherchannel port-channel 
---
S3#show interfaces trunk 
S3#show etherchannel summary 
S3#show etherchannel port-channel

Part 3: Configure an 802.3ad LACP EtherChannel

S1(config)#interface range gigabitEthernet 0/1-2
S1(config-if-range)#shutdown 
S1(config-if-range)#channel-group 2 mode active 
S1(config-if-range)#no shutdown
S1(config-if-range)#exit
S1(config)#interface port-channel 2
S1(config-if)#switchport trunk encapsulation dot1q 
S1(config-if)#switchport mode trunk

S2(config)#interface range gigabitEthernet 0/1-2
S2(config-if-range)#channel-group 2 mode active
S2(config-if-range)#no shutdown
S2(config-if-range)#exit
S2(config)#interface port-channel 2
S2(config-if)#switchport trunk encapsulation dot1q 
S2(config-if)#switchport mode trunk

Part 4: Configure a Redundant EtherChannel Link

S2(config)#interface range fastEthernet 0/23-24
S2(config-if-range)#shutdown 
S2(config-if-range)#channel-group 3 mode passive 
S2(config-if-range)#no shutdown 
S2(config)#interface port-channel 3
S2(config-if)#switchport trunk encapsulation dot1q 
S2(config-if)#switchport mode trunk

S3(config)#interface range fastEthernet 0/23-24
S3(config-if-range)#channel-group 3 mode passive 
S3(config-if-range)#no shutdown 
S3(config)#interface port-channel 3
S3(config-if)#switchport trunk encapsulation dot1q 
S3(config-if)#switchport mode trunk

Part 5: STP Configuration

S1(config)#spanning-tree mode rapid-pvst 
S1(config)#spanning-tree vlan 99,100 root primary 
S1(config)#spanning-tree vlan 200 root secondary

S3(config)#spanning-tree vlan 200 root primary 
S3(config)#spanning-tree vlan 99,100 root secondary 

S2(config)#spanning-tree mode rapid-pvst 
S2(config)#spanning-tree vlan 99,100,200 priority 36864

S3#show spanning-tree active 
S1#show spanning-tree active

Part 6: Verify LACP and PAgP Configuration





EtherChannel Configuration Guidelines and Restrictions -

  1. All Ethernet interfaces support EtherChannel up to a maximum of eight interfaces with no requirement that the interfaces be on the same interface module.
  2. All interfaces within an EtherChannel must operate at the same speed and duplex.
  3. EtherChannel links can function as either single VLAN access ports or as trunk links between switches.
  4. All interfaces in a Layer 2 EtherChannel must be members of the same VLAN or be configured as trunks.
  5. If configured as trunk links, Layer 2 EtherChannel must have the same native VLAN and have the same VLANs allowed on both switches connected to the trunk.
  6. When configuring EtherChannel links, all interfaces should be shutdown prior to beginning the EtherChannel configuration. When configuration is complete, the links can be re-enabled.
  7. After configuring the EtherChannel, verify that all interfaces are in the up/up state.
  8. It is possible to configure an EtherChannel as static, or for it to use either PAgP or LACP to negotiate the EtherChannel connection. The determination of how an EtherChannel is setup is the value of the channel-group number mode command. Valid values are:
    1. active - LACP is enabled unconditionally
    2. passive - LACP is enabled only if another LACP-capable device is connected.
    3. desirable - PAgP is enabled unconditionally
    4. auto - PAgP is enabled only if another PAgP-capable device is connected.
    5. on - EtherChannel is enabled, but without either LACP or PAgP.
  9. LAN ports can form an EtherChannel using PAgP if the modes are compatible. Compatible PAgP modes are: 
    1. desirable => desirable desirable => auto. (If both interfaces are in auto mode, an Etherchannel cannot form.)
  10. LAN ports can form an EtherChannel using LACP if the modes are compatible. Compatible LACP modes are:
    1. active => active active => passive. (If both interfaces are in passive mode, an EtherChannel cannot form using LACP.)
  11. Channel-group numbers are local to the individual switch. Although this activity uses the same Channel-group number on either end of the EtherChannel connection, it is not a requirement. Channel-group 1 (interface po1) on one switch can form an EtherChannel with Channel-group 5 (interface po5) on another switch.





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