EtherChannel

 

ETHERCHANNEL/PORTCHANNEL

EtherChannel which is also known as link aggregation. EtherChannel is a technology that lets you bundle multiple physical links into a single logical link.

·         Fault-tolerant, high-speed links between switches and routers

·         Automatic recovery for the loss of a link by redistributing the traffic across the remaining links

·         STP will not block one of the links in the bundle, because to STP the bundle looks like a single link

·         Up to 8 links can be combined to provide more bandwidth

·         The links within the bundle must have the same characteristics such as duplex, speed, etc.

·         EtherChannel can be configured as Layer 2 or Layer 3

·         With Layer 3, a logical interface (Port channel) is statically configured and all Layer 3 configurations are performed under that interface

·         With Layer 2, the logical interface is created automatically

·         With both Layer 2 and Layer 3, physical interfaces must be manually assigned to the logical interface using the "channel-group" command

·         EtherChannels can be configured automatically using Port Aggregation Protocol (PAgP} or Link Aggregation Control Protocol (LACP)

·         PAgP is a Cisco proprietary protocol, whereas LACP is an industry-standard IEEE 802.3ad protocol

·         Switches can be configured to use PAgP by configuring them in AUTO or DESIRABLE mode

·         Switches can be configured to use LACP by configuring them in ACTIVE or PASSIVE mode

·         If the switches are configured in ON mode, they will not exchange LACP or PAgP packets

 

If you want to configure an EtherChannel then we have three options:

• PAgP (Cisco proprietary)
• LACP (IEEE standard)
• Manual

·         PAgP and LACP are negotiation protocols that dynamically configure an EtherChannel. PAgP is a Cisco proprietary protocol so you can only use it between Cisco devices. LACP is an IEEE standard which many vendors support.

·         It’s also possible to configure a static EtherChannel without these protocols doing the negotiation of the link for you.

·         If you are going to create an EtherChannel you need to make sure that all interfaces have the same configuration:

·         Duplex.

·         Speed.

·         Native and allowed VLANs.

·         Switchport mode (access or trunk).

PAgP and LACP will check if the configuration of the interfaces that you use is the same.

EtherChannel Mode-

 

1.      ON - Forces the interface into an EtherChannel without PAgP or LACP packets, both switches must be configured in ON mode for the EtherChannel to be established.

2.      ACTIVE - Used in LACP - the switches will actively negotiate an EtherChannel link.

3.      PASSIVE - Used in LACP - places the interface in a passive negotiation mode where it only responds to LACP packets that it receives. In this mode, the switch will not start the negotiation process; this setting minimizes the transmission of LACP packets.

4.      AUTO - Used in PAgP_ - places the interface in a passive negotiation mode; it only responds to PAgP packets that it receives. In this mode, the switch will not start the negotiation process; this setting minimizes the transmission of PAgP packets.

5.      DESIRABLE - Used in PAgP - the switches will actively negotiate an EtherChannel link.

 

Layer 2 EtherChannel

 

·         Configure the "default interface" for the interfaces involved.

·         Assign a channel-group and channel-group number to the physical interfaces, this step will create a port-channel interface automatically.

·         Configure the trunking encapsulation directly in port-channel interface configuration mode.

·         Reset the ports in the group by entering "shut" and then, "no shut".

 

Configuration-

 

SW-l(config)#default interface range f0/19-20

SW-l(config)#interface range f0/19-20

SW-l(config-if-range)#No shut

SW-l(config-if-range)#channel-group 22 mode Auto/Desirable/

SW-l(config)#int port-channel 22

SW-l(config-if)#switchport trunk encapsulation dotlq

SW-l(config-if)#switchport mode trunk

 

SW-2(config)#default interface range f0/19-20

SW-2(config)#interface range f0/19-20

SW-2(config-if-range)#No shut

SW-2(config-if-range)#channel-group 22 mode Auto/Desirable/

SW-2(config)#int port-channel 22

SW-2(config-if)#switchport trunk encapsulation dotlq

SW-2(config-if)#switchport mode trunk

 

Verification-

 

SW#show etherchannel summary

SW-l#Show run interface port-channel 22 lb inter

SW#show interface Port-channel22

SW-l#Show interface trunk I inc 802

 

Layer3 EtherChannel-

 

·         Default interface the physical interfaces

·         Configure the interface port-channel

·         Configure the port-channel interface with "no switchport" and then configure the IP address

·         Configure the physical interfaces with " no switchport "

·         Assign the port-channel ID to the interfaces using the channel-group interface configuration command

·         Reset the physical interfaces by using "shut" and "no shut"

 

Configuration-

 

On SW-3:

SW-2(config)#default interface range f0/23-24

SW-2(config)#int port-channel 13

SW-2(config-if)#NO switchport

SW-2(config-if)#ip addr 10.1.23.2 255.255.255.0

 

SW-2(config)#int range f0/23-24

SW-2(config-if-range)#NO switchport

SW-2(config-if-range)#NO shut

SW-2(config-if-range)#channel-group 13 mode on

SW-2(config-if)#NO shut

SW-2(config)#int range f0/23-24

 

On SW-3:

SW-3(config)#default interface range f0/23-24

SW-3(config)#int port-channel 31

SW-3(config-if)#No switchport

SW-3(config-if)#ip addr 10.1.23.3 255.255.255.0

SW-3(config)#int range f0/23-24

SW-3(config-if-range)#channel-group 31 mode on

 

Note: If the "no switchport" interface command is not configured, you will get an error.

SW-3(config-if-range)#No switchport

SW-3(config-if-range)#channel-group 31 mode on

SW-3(config-if-range)#No shut

SW-3(config)#int range f0/23-24

SW-3(config-if-range)#shut

SW-3(config-if-range)#No shut

 

To verify and test the configuration: On SW-2:

SW-2#Show etherchannel summary 

 

EtherChannel Load Balancing-

EtherChannel balances the traffic load across the links in a channel. It uses the binary pattern that the addresses in the frame form a numerical value and according to that value, EtherChannel selects one of the links in the channel.

 

EtherChannel load balancing can use MAC addresses or IP addresses, source or destination addresses, or both source and destination addresses. The mode applies to all EtherChannels that are configured on the switch. By default src-mac load balancing method enable on switches.

 

You configure the load balancing by the command: port-channel load-balance {dst-ip | dst-mac | src-dst-ip | src-dst-mac | src-ip | src-mac} 

 

You can find out which interface is used in the EtherChannel to forward traffic based on the load balancing method. The command for this determination is test etherchannel load-balance interface port-channel number {ip | mac} [source_ip_add|source_mac_add] [dest_ip_add|dest_mac_add]

 

SW1#show EtherChannel load-balance

 

There are plenty of options to choose from, including combinations of source and/or destination MAC or IP addresses.

 

SW1(config)#port-channel load-balance ?

  dst-ip       Dst IP Addr

  dst-mac      Dst Mac Addr

  src-dst-ip   Src XOR Dst IP Addr

  src-dst-mac  Src XOR Dst Mac Addr

  src-ip       Src IP Addr

  src-mac      Src Mac Addr