Get Started with EtherChannel: Enhance Your Network

EtherChannel or Port-Channel or Eth-Trunk is a link aggregation technology in which multiple physical port links are grouped into one logical link to provide-

Today, we will do deep drive in EtherChannel. Let’s get Started with EtherChannels which is sometimes refered as port-channel or LAG (link aggregation) or Eth-Trunk.

EtherChannel Types

There are two types of link aggregation protocols. These are-

Static Link Aggregation

This is manual link aggregation, where multiple links will be aggregated into one to provide higher interface throughput and redundancy. This is mainly configured where dynamic is not supported or topology rarely changes.

Configuration is very simple for Static Link Aggregation. The only condition is, both switches must need to enable mode “ON”. Any other combination will not work.

Sx Switch
Sx(config-if-range)#channel-group 1 mode on

Sy Switch
Sy(config-if-range)#channel-group 1 mode on

Dynamic Link Aggregation

Dynamic Link Aggregation is a method to automatically bundle multiple physical links into a single logical link. Similar to static link aggregation, it increases higher bandwidth and better redundancy.

Dynamic link aggregation is divided into two categories.

What is LACP?

LACP is IEEE 802.3ad standard, that means it’s open and it can be configured in any OEM like Cisco, Juniper, Huawei. We can create with maximum 16 links, with 8 will be in active state and remaining 8 links in standbay.

Link Aggregation Control Protocol (LACP) works in two (2) modes. These are –

SWITCH(config-if-range)#channel-group 1 mode ?
  active     Enable LACP unconditionally
  passive    Enable LACP only if a LACP device is detected

Understanding LACP Active Mode

In this mode, the network device sends LACP packets to it’s peer device to form port-channel. Consequently, peer end can configure either Active or Passive.

Active/Active
Sx Switch
Sx(config-if-range)#channel-group 1 mode active

Sy Switch
Sy(config-if-range)#channel-group 1 mode active

Active/Passive
Sx Switch
Sx(config-if-range)#channel-group 1 mode active

Sy Switch
Sy(config-if-range)#channel-group 1 mode passive

Understanding LACP Passive Mode

Here, network device doesn’t transmit any LACP packets, but instead wait to receive LACP packets from peer node. That means. the other node must be LACP active to establish LACP between two nodes.

Active/Passive
Sx Switch
Sx(config-if-range)#channel-group 1 mode passive

Sy Switch
Sy(config-if-range)#channel-group 1 mode active

But, if you configure Passive/Passive mode, then eth-trunk (port-channel) will not be established. Because, both swtiches will wait to receive LACP neighborship packets which will never be received.

What is PAgP?

PAgP is Cisco proprietary protocol. It can marge eight (8) links into one virtual link. PAgP works in two (2) modes-

Understanding PAgP Desirable Mode

It’s similar to LACP active mode. Here network device actively sends PAgP packets to establish port-channel. Peer end can configure either desirable or auto mode to establish PAgP.

Desirable/Desirable
Sx Switch
Sx(config-if-range)#channel-group 1 mode desirable

Sy Switch
Sy(config-if-range)#channel-group 1 mode desirable

Desirable/Auto
Sx Switch
Sx(config-if-range)#channel-group 1 mode desirable

Sy Switch
Sy(config-if-range)#channel-group 1 mode auto

Understanding PAgP Auto Mode

In this mode, node don’t send any PAgP packets, but it’s wait for PAgP packets. If it received any packets from desirable enabled node, it will establish. Below are the plan you need to follow to form PAgP peer.

Desirable/Auto
Sx Switch
Sx(config-if-range)#channel-group 1 mode auto

Sy Switch
Sy(config-if-range)#channel-group 1 mode desirable

Upcoming post on EtherChannel

• How to configure EtherChannel in Cisco
• Understanding LACP load-balancing mechanism
• Troubleshooting Port Channels

If you have any questions on link aggregation, feel free to ask.