Ether Channel

Understanding Ether Channel Configuration Types of Ether channel Manual Ether Channel configuration Ether Channel – Dynamic Configuration

IEEE Link Aggregation Protocol (LACP) - Industry Standard Port Aggregation Protocol (PAGP) - Cisco Proprietary protocol

Troubleshooting Ether Channel

Understanding Ether Channel Port aggregation allows multiple physical ports to be bundled together to form a single logical port. The switch and STP will treat the bundled ports as a single interface, eliminating the possibility of a switching loop.

Ether Channel is a port link aggregation technology developed by Cisco, which provides fault-tolerant high-speed links between Switches, Routers, and Servers.

Ether Channel technology can be used to increase the bandwidth between two devices that support Ether Channel technology and Ether Channel technology provides automatic recovery for the loss of a link by redistributing the load across the remaining links.

However, simply trunking two or more ports between the switches will not work, as this creates a switching loop. One of two things will occur:

Spanning Tree Protocol (STP) will disable one or more ports to eliminate the loop.

If STP is disabled, the switching loop will result in an almost instantaneous broadcast storm, crippling the network

There are two issues with using only a single physical port for the trunk connection:

The port represents a single point of failure. If the port goes down, the trunk connection is lost.

Thus, the obvious benefits of adding redundancy to the trunk connection are fault tolerance and increased bandwidth, via load balancing

Port aggregation allows multiple physical ports to be bundled together to form a single logical port. The switch and STP will treat the bundled ports as a single interface, eliminating the possibility of a switching loop.

Cisco’s implementation of port aggregation is called Ether Channel. EtherChannel supports Fast, Gigabit, and 10 Gigabit Ethernet ports. A maximum of 8 active ports are supported in a single Ether Channel.

Cisco IOS Release 12.2SX supports a maximum of 128 EtherChannels. You can form an EtherChannel with up to eight compatibly configured LAN ports on any switching module. All LAN ports in each EtherChannel must be the same speed and must all be configured as either Layer 2 or Layer 3 LAN ports.

Types of Ether channel There are two methods of configuring an EtherChannel:

Manually Dynamically

Manually:Manually configured EtherChannel ports do not exchange EtherChannel protocol packets. A manually configured EtherChannel forms only when you configure all ports in the EtherChannel compatibly.

Configuration of etherchannel manually:

Adding switch ports to a channel-group creates a logical port-channel interface. This interface can be configured by referencing the channelgroup number: SWITCH A SWITCH B Switch A(config)# interface range gi0/1 – 4 Switch B(config)# interface range gi0/1 - 4 Switch A(config-if)# channel-group 1 mode on Switch B(config-if)# channel-group 1 mode on

Changes made to the logical port-channel interface are applied to all physical switch ports in the channel-group:Switch A(config)# interface port-channel 1

Switch A(config-if)# switchport mode trunk Switch A(config-if)# switchport trunk allowed vlan 5-10Switch A(config-if)# no shut

Switch B(config)# interface port-channel 1 Switch B(config-if)# switchport mode trunk Switch B(config-if)# switchport trunk allowed vlan 5-10Switch B(config-if)# no shut

EtherChannel – Dynamic ConfigurationCisco switches support two dynamic aggregation protocols:

PAgP (Port Aggregation Protocol) – Cisco proprietary aggregatin protocol.LACP (Link Aggregation Control Protocol) – IEEE standardized aggregation protocol, originally defined in 802.3ad

PAgP (Port Aggregation Protocol) PAgP is a Cisco-proprietary aggregation protocol. PAgP supports the automatic creation of EtherChannels by exchanging PAgP packets between LAN ports. PAgP packets are exchanged only between ports in auto and desirable modes. Desirable – actively attempts to form a channel

Auto – waits for the remote switch to initiate the channel A PAgP channel will form in the following configurations

desirable >> desirable desirable >> auto

SWITCH A SWITCH B

Switch A(config)# interface range gi0/1 – 4 Switch B(config)# interface range gi0/1 - 4

Switch(config-if)# channel-protocol pagp Switch(config-if)# channel-protocol pagp

Switch A(config-if)# channel-group 1 mode auto Switch B(config-if)# channel-group 1 mode desirable

Switch A(config)# interface port-channel 1 switch B ----same like as above configuration. Switch A(config-if)# switchport mode trunk Switch A(config-if)# switchport trunk allowed vlan 5-10Switch A(config-if)# no shut

EtherChannel – LACPLACP is an IEEE standard aggregation protocol, and supports two modes. LACP supports the automatic creation of EtherChannels by exchanging LACP packets between LAN ports. LACP packets are exchanged only between ports in passive and active modes.

Active – actively attempts to form a channel

Passive – waits for the remote switch to initiate the channel

An LACP channel will form in the following configurations:

Active== active Active ==passive

SWITCH A SWITCH B Switch A(config)# interface range gi0/1 – 4 Switch B(config)# interface range gi0/1 - 4

Switch(config-if)# channel-protocol lacp Switch(config-if)# channel-protocol lacp

Switch A(config-if)# channel-group 1 mode active Switch B(config-if)# channel-group 1 mode passive

Switch A(config)# interface port-channel 1 Switch A(config-if)# switchport mode trunk Switch A(config-if)# switchport trunk allowed vlan 5-10Switch A(config-if)# no shut

Switch B(config)# interface port-channel 1 Switch B(config-if)# switchport mode trunk Switch B(config-if)# switchport trunk allowed vlan 5-10Switch B(config-if)# no shut

Recall that a maximum of 8 active ports are supported in a single EtherChannel. LACP supports adding an additional 8 ports into the bundle in a standby state, to replace an active port if it goes down. LACP assigns a numerical port-priority to each port, to determine which ports become active in the EtherChannel. By default, the priority is set to 32768, and a lower priority is preferred. If there is a tie in port-priority, the lowest port number is preferred. To change the LACP port-priority to something other than default:

Switch(config)# interface range fa0/1-4 Switch(config-if)# lacp port-priority 100

Troubleshooting EtherChannelTo view status information on all configured EtherChannels:

Switch# show etherchannel summary Switch# show etherchannel portchannel

This example shows how to verify the configuration of EtherChannel 1

switch# show running interfaces port-channel 1