EtherChannel

Done

EtherChannel is the aggregation of multiple physical interfaces into one logical interface

Other names include:

Port Channel

LAG (Link Aggregation Group)

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When the bandwidth of the end hosts connected to the access switch is greater than the one to the distribution switches, it is called oversubscription. However, some oversubscription is acceptable, since not always the total bandwidth is used.

EtherChannel load balances the forwarding of frames based on “flows”, which are basically a connection between two nodes (devices). In a specific node, it will use the same interface for all frames. The calculation of which interface to use, uses the following inputs:

Source MAC Address

Destination MAC Address

Source AND Destination MAC Address

Source IP Address

Destination IP Addresses

Source AND Destination IP Addresses

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Some switches may support only layer 2 and/or layer 3 inputs.

See the EtherChannel Load-Balance Method being used

show etherchannel load-balance

Change the EtherChannel Load-Balance Method

configure terminal // Global Configuration Mode
port-channel load-balance {method} // Notice that etherchannel is named as port-channel

EtherChannel Protocols

PAgP (Port Aggregation Protocol)

It is a Cisco Proprietary protocol, similar to DTP. It will negotiate the creation/maintenance of the EtherChannel.

Create a PAgP EtherChannel

configure terminal
interface range g0/0 - 3
channel-group {number} mode {auto/desirable}

The number has to match in all the interfaces on the same switch, however, it doesn`t matter relative to the other switch, it can be another number.

Desirable
- As DTP, it will actively try to form a EtherChannel link

Auto
- As DTP, it will not form a EtherChannel unless paired with a Desirable one

LACP (Link Aggregation Control Protocol)

It is a IEEE standard, numbered 802.3ad. As PAgP, it will negotiate the creation/maintenance of the EtherChannel.

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PAgP only supports up to 8 interfaces linked together in a EtherChannel. However, LACP supports up to 16 (8 active and 8 in standy-by).

Create LACP EtherChannel

configure terminal
interface rage g0/0 - 3
channel-group {number} mode {active/passive}

Active = Desirable

Passive = Auto

Static EtherChannel

It is the least used one, since if a link fails, it will still try to use that interface, once it is not negotiated.

configure terminal
interface range g0/0 - 3
channel-group {number} mode on

Explicitly change the EtherChannel Protocol (not necessary)

configure terminal
interface range g0/0 - 3
channel-protocol {lacp/pagp}

Which ports are bundled and which are in Hot-Standby?

This determined by the LACP Port Priority with each port, and if they are the same, the lower port number will be active.

Even if you set the port priority to a lower number, it can stay in hot-standby, but why?

This happens because the device if the lowest Device ID (Mac Address) will dictate which ports are active and which are in standby, assuming both have the default system priority of 32768.

Change Port Priority

configure terminal
interface g0/1
lacp port-priority 100 // The default is 32768

Change a Device`s Priority

configure terminal
lacp system-priority 100 // T

See EtherChannel information

Summary

show etherchannel summary

Port-channel

show etherchannel port-channel

Will a EtherChannel work?

Only if both switches/routers have:

Same Duplex

Same Speed

Same Allowed VLANs

Same Switchport Mode (Access/Trunk)

PAgP “non-silent”

this optional parameter when configuring channel-group {number} mode {auto/desirable} [non-silent] is used to make ports being added to a EtherChannel group only if the port on the other side is also PAgP capable and configured.