What is EtherChannel ? Configuration Example

By | 9th November 2015

EtherChannel Configuration on Cisco Switches.

By configuring EtherChannel, we are bundling multiple physical connections between two or more Cisco switches into one logically link.

In a conventional network where STP blocks one link to avoid switching loops, Etherchannel forces STP to see both paths or bundled as one logical link while avoiding switching loops.

Cisco IOS Release 15.0SY supports a maximum of 128 EtherChannels.

You can create an EtherChannel with up to eight 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.

You can configure EtherChannels manually or you can use the Port Aggregation Control Protocol (PAgP) or the Link Aggregation Control Protocol (LACP) to create EtherChannels.




 The EtherChannel protocols allow ports with similar characteristics to form an EtherChannel through dynamic negotiation with connected network devices. PAgP is a Cisco-proprietary protocol while LACP is standard or multi-vendor as defined in IEEE 802.3ad.

Ports configured to use PAgP cannot form EtherChannels with ports configured to use LACP also ports configured to use LACP cannot form EtherChannels with PAgP.

Guidelines for Configuring EtherChannel
• PAgP is Cisco proprietary.
• LACP is defined in 802.3ad.
• You can combine from two to eight parallel links.
• All ports must be identical:
— Same speed and duplex
— Cannot mix Fast Ethernet and Gigabit Ethernet
— Cannot mix PAgP and LACP
— Must all be VLAN trunk or nontrunk operational status
• All links must be either Layer 2 or Layer 3 in a single channel group.
• To create a channel in PAgP, sides must be set to
— Auto-Desirable
— Desirable-Desirable
• To create a channel in LACP, sides must be set to
— Active-Active
— Active-Passive
• To create a channel without using PAgP or LACP, sides must be set to On-On.
• Donot configure a GigaStack gigabit interface converter (GBIC) as part of an
EtherChannel.
An interface that is already configured to be a Switched Port Analyzer (SPAN)
destination port will not join an EtherChannel group until SPAN is disabled.
• Donot configure a secure port as part of an EtherChannel.
• Interfaces with different native VLANs cannot form an EtherChannel.
• When using trunk links, ensure all trunks are in the same mode—Inter-Switch Link
(ISL) or dot1q.

We will use the network topology below as example.

SW1 and SW2 are connected by two crossover cables, one cable connecting port fa0/1 on both switches and the other connecting fa0/2 on both switches.

Understanding EtherChannel Configuration on Cisco Switches1




We will use the network topology below as example.

SW1 and SW2 are connected by two crossover cables, one cable connecting port fa0/1 on both switches and the other connecting fa0/2 on both switches.

Understanding EtherChannel Configuration on Cisco Switches2

After your configuration, use the show show spanning-tree command to view spanning-tree for VLAN 1; you will see only a port-channel, the spanning-tree cost and you will also notice that the port-channel is now being considered as spanning-tree type shared.




You can add more physical ports, Spanning tree will see the logical port-channel  as a single port.

Understanding EtherChannel Configuration on Cisco Switches3

Host Standby Router Redundancy Protocol (HSRP)

Virtual Router Redundancy Protocol (VRRP)

Gateway Load Balancing Protocol (GLBP)

Understanding Simple Network Management Protocol-SNMP

Spanning Tree Protocol (STP)

VLAN Trunking Protocol (VTP)

IPv6 Explained

EIGRPv6

RIPv6 or RIPng

OSPFv3

DHCPv6




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