CCNA

Creating Layer 2 and Layer 3 Ether Channels

Jay

29 Aug 2009 • 2 min read

EtherChannel technology allows network administrators to bundle multiple physical links into a single logical link. This bundling provides increased bandwidth and redundancy between network devices. There are two primary types of EtherChannels: Layer 2 (for switched networks) and Layer 3 (for routed networks).

Layer 2 EtherChannel Configuration

Layer 2 EtherChannels are used between switches to create high-bandwidth trunk links or access links. The configuration involves grouping multiple switch ports into a single logical interface.

Basic Layer 2 EtherChannel Setup

To configure a Layer 2 EtherChannel, you need to:

Enter interface configuration mode for the desired interfaces
Configure the channel-group with the same number on all participating interfaces
Configure the port-channel interface

Switch(config)# interface range FastEthernet0/1 - 2
Switch(config-if-range)# channel-group 1 mode active
Switch(config-if-range)# exit
Switch(config)# interface port-channel 1
Switch(config-if)# switchport mode trunk
Switch(config-if)# switchport trunk allowed vlan all

EtherChannel Negotiation Protocols

There are three modes for EtherChannel negotiation:

LACP (Link Aggregation Control Protocol) - Uses active and passive modes
PAgP (Port Aggregation Protocol) - Uses desirable and auto modes
Static - Uses on mode (no negotiation)

! LACP Configuration
Switch(config-if-range)# channel-group 1 mode active

! PAgP Configuration  
Switch(config-if-range)# channel-group 1 mode desirable

! Static Configuration
Switch(config-if-range)# channel-group 1 mode on

Layer 3 EtherChannel Configuration

Layer 3 EtherChannels are used between routers or Layer 3 switches to create high-bandwidth routed links. These interfaces can have IP addresses assigned and participate in routing protocols.

Basic Layer 3 EtherChannel Setup

Layer 3 EtherChannel configuration requires switching the interfaces to routed mode before bundling:

Router(config)# interface range GigabitEthernet0/1 - 2
Router(config-if-range)# no switchport
Router(config-if-range)# channel-group 1 mode active
Router(config-if-range)# exit
Router(config)# interface port-channel 1
Router(config-if)# ip address 192.168.1.1 255.255.255.0
Router(config-if)# no shutdown

Layer 3 EtherChannel with Routing Protocols

Once configured, Layer 3 EtherChannels can participate in routing protocols like OSPF or EIGRP:

Router(config)# router ospf 1
Router(config-router)# network 192.168.1.0 0.0.0.255 area 0

Router(config)# router eigrp 100
Router(config-router)# network 192.168.1.0 0.0.0.255

Verification Commands

Several commands help verify EtherChannel operation:

! Show EtherChannel summary
Switch# show etherchannel summary

! Show detailed EtherChannel information
Switch# show etherchannel detail

! Show port-channel interfaces
Switch# show interface port-channel 1

! Show LACP information
Switch# show lacp neighbor

Best Practices and Troubleshooting

When implementing EtherChannels, consider these important points:

All interfaces in an EtherChannel must have identical configurations
Speed, duplex, and VLAN settings must match across all member interfaces
Use consistent negotiation modes on both sides of the link
Monitor for error messages indicating configuration mismatches

Common troubleshooting commands include:

Switch# show etherchannel load-balance
Switch# show spanning-tree interface port-channel 1
Switch# debug etherchannel events

EtherChannel technology provides an excellent solution for increasing bandwidth and redundancy in both switched and routed network environments. Proper configuration and verification ensure optimal network performance and reliability.