ETHERCHANNEL: CONDITIONS, DEFAULT CONFIG, LEARNING METHOD, LOAD BALANCING


TOPICS

ETHERCHANNEL CONDITIONS

ETHERCHANNEL DEFAULT CONFIGURATION

ETHERCHANNEL LEARNING METHOD

ETHERCHANNEL LOAD BALANCING


 

ETHERCHANNEL CONDITIONS

 

Each EtherChannel can have up to eight compatibly configured Ethernet interfaces

Configure all interfaces in an EtherChannel to operate at the same speeds and duplex modes

Enable all interfaces in an EtherChannel. An interface in an EtherChannel disabled by using the shutdown interface configuration command is treated as a link failure, and its traffic is transferred to one of the remaining interfaces in the EtherChannel.

 

When a group is first created, all ports follow the parameters set for the first port to be added to the group. If you change the configuration of one of these parameters, you must also make the changes to all ports in the group:

Allowed-VLAN list

STP path cost for each VLAN

STP port priority for each VLAN

STP Port Fast setting

 

Before enabling 802.1X on the port, you must first remove it from the EtherChannel. If you try to enable 802.1X on an EtherChannel or on an active port in an EtherChannel, an error message appears, and 802.1X is not enabled. If you enable 802.1X on a not-yet active port of an EtherChannel, the port does not join the EtherChannel.

 

An EtherChannel does not form if one of the interfaces is a Switch Port Analyzer (SPAN) destination port.

 

An Etherchannel does not form, if ports are configured with Dynamic VLAN’s

 

If ports are access ports, they should all be part of the same VLAN

 

If ports are trunk ports, allowed VLAN’s on trunk ports should be same

 

All the trunks configured in etherchannel must have same Native VLAN

 

Trunking encapsulation should be same on all the trunk ports


ETHERCHANNEL DEFAULT CONFIGURATION

 

Feature
Default Setting
Channel groups None assigned.
Layer 3 port-channel logical interface None defined.
PAgP mode Auto and silent (The interface is in a passive negotiating state; it responds to PAgP packets it receives but does not start PAgP packet negotiation. PAgP is enabled only if a PAgP device is detected.)
PAgP learn method Aggregate-port learning on all interfaces.
PAgP priority 128 on all interfaces.
Load balancing Load distribution on the switch is based on the source-MAC address of the incoming packet. Load distribution based on the source and destination IP address is also enabled for routed IP traffic.

ETHERCHANNEL LEARNING METHOD

 

LEARNING METHOD

Network devices are classified as PAgP physical learners or aggregate-port learners. A device is a physical learner if it learns addresses by physical ports and directs transmissions based on that knowledge. A device is an aggregate-port learner if it learns addresses by aggregate ports

 

Compatibility Issues

Example

Catalyst 3550 switch supports address learning only on aggregate ports

Catalyst 1900 switch supports address learning by physical ports

Solution

When the link partner to the Catalyst 3550 switch is a physical learner, we recommend that you configure the switch as a physical-port learner by using the pagp learn-method physical-port interface configuration command

 

Note

Above Learning method has nothing to do with the Load Balancing. Learning method relates to the communication between switches forming the Etherchannel


ETHERCHANNEL LOAD BALANCING

 

Point To Note

EtherChannel load balancing can use MAC addresses, IP addresses, or Layer 4 port numbers

The mode you select applies to all EtherChannels that you configure on the switch

Catalyst 6500/6000 switches that run Cisco IOS® system software support a maximum of 64 EtherChannels

In Each Etherchannel, there can be 8 links bundled

 

Command to enable Load Balancing 

port-channel load-balance {src-mac | dst-mac | src-dst-mac | src-ip | dst-ip | src-dst-ip | src-port | dst-port | src-dst-port | mpls

As we can see, there are options based on the

source or destination mac

source or destination ip

source-destination mac

source-destination ip

source port

destination port

source-destination port

 

How to select Load Balancing method ?

Example: we have 4 hosts connected to the switch accessing a single server

Here, source are 4 and destination is only 1

So, in this case, best option to utilize maximum no. of  links is to go with Source mac based  load balancing

 

 

 

 

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