Logically bonding physical links together.
Consists of Logical interface called port-channel, and physical member interfaces configured to be bundled together.
Hides physical interfaces from upper level protocols like STP.
Individual flows cannot surpass the bandwidth of an individual physical link.
Multichassis Link Aggregation:
Etherchannel spread across multiple switches.
Often used in Cisco Stackwise or vPC.
Two separate switches need to somehow share the Etherchannel control plane.
- Supported but not recommended.
- Failure to properly setup LAG can cause L2 loop.
- Etherchannel Guard can help mitigate this.
- Link Aggregation Control Protocol
- IEEE 802.3ad – standard
- sw1(config-int)#channel-group <#> mode <mode>
- No negotiation.
- Dangerous, not recommended
- Initiate LACP negotiation with other side
- Listen for LACP negotiation from other side
Etherchannel Load Balancing:
- Source and Destination MAC address
- Source and Destination IP Address
- Source and Destination Layer 4 protocol and/or socket
- Load Balancing is locally significant.
- A port-channel between two switches does not need to match load balancing methods on each side.
- Verification that port-channel is up can be done with show etherchannel summary or show int port-channel1 etherchannel:
- Once verified, load balancing can be changed via ‘port-channel load-balance <method>
Layer 3 Etherchannel:
- Order of operation matters.
- When creating routed port-channel interface, do no switchport 1st on physical interfaces, then add them to LAG.