EtherChannel
Day 23
EtherChannel
If you connect two switches together with multiple interfaces, all except one will be disabled by the STP. It is a waste of bandwidth. EtherChannel groups multiple physical interfaces together to act as a single logical interface. Traffic using the EtherChannel is load balanced among the physical interfaces. EtherChannel is also known as PortChannel, LAG (Link Aggregation Group).
ASW - Access Layer Switch, a switch that end hosts connect to.
DSW - Distribution Layer Switch, a switch that access switches connect to.
Load Balancing
EtherChannel load balances based on the flows. A flow is a communication between two nodes. Frames in the same flow are forwarded using the same physical interface. Depending on the switch, configuration settings for interface selection calculation can be changed based on these:
Source MAC address
Destionat MAC address
Source and Destination MAC address
Source IP address
Destination IP address
Source and Destination IP address
To see the current load balancing method, use show etherchannel load-balance command from the privileged EXEC mode. To change the config settings, enter the global config mode and use the command port-channel load-balance followed by the method.
Protocols
There are 3 methods of EtherChannel configuration: PAgP (Port Aggregation Protocol), LACP (Link Aggregation Control Protocol), and Static. Up to 8 interfaces can be formed into a single EtherChannel. LACP allows up to 16 but only 8 will be active, the other 8 will be in standby mode. LACP is IEEE 802.3ad standard.
Configuration
It is better to configure interfaces in a bunch using the interface range command. Enter the interface config mode and use the channel-group followed by virtual interface number followed by mode and the mode you want to use. auto and desirable modes are used for PAgP similarly to DTP. PortChannel gets created automatically. active and passive modes are used for LACP. If both ends are configured in passive mode, EtherChannel won't be formed. In all other cases, it forms an EtherChannel. on mode configures Static EtherChannel. It doesn't work with other modes. To manually configure the negotiation protocol, enter the channel-protocol command followed by the mode (lacp/pagp). To verify the EtherChannel config settings, enter show etherchannel summary or show etherchannel port-channel.
Member interfaces must have matching configurations:
Duplex
Speed
Switchport mode
VLAN settings
If an interface's configurations don't match the others, it is excluded from the EtherChannel.
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