5 - Etherchannel

ETHERCHANNEL

HOW IT WORKS

- Two parts
  - Logical Interface representing the link bundle
  - Physical links    menber interfaces part of the link bundle
- Trick the STP so it doesn't see individual menbers but a single portchannel

PROS

- Cheap incremental upgrade solution
- Add link later redundancy

CONS

- Flow can't not be load balance between multiple members of the channel
  - Analogy: It is like adding links to the highway but the speed is the same
- Flows can get polirized to one member

MULTICHASSIS ETHERCHANNEL

- Resolves the single point of failure of having one switch (Single chassis Etherchannel)
- Multichassis forms a logical chassis between two physical switches
- Server thinks has two connections to the same switch
- Cisco proporse three solutions:
  - Stackwise: Can have more than two members limit depends on platform Ej: 9 on 3750-x
  - Vss and vPC are always a pair of switches

ETHERCHANNEL NEGOCIATION PROTOCOL

- Two forms of LAG negotition
  - Port Aggregation Protocol (PAgP): Cisco propietary, LACP pre-standard
  - Link Aggregation Control Protocol (LACP): IEEE standard 802.3ad
-  Static LAG negotiation is possible but not recommend (mode on)
   - If one of the sides is not properly configured can cause a loop
   - EtherChannel Guard mitigate this (part of the spanning tree process)

ETHERCHANNEL NEGOTIATION MODES

- On : No negotiation (the protocols PAgP and LACP are disabled)
- Desirable & auto : Initiate or listen for PAgP
- Actve & Passive  : Iniatiate or listen for LACP

ETHERCHANNEL MODE NEGOTIATION

- On - On  (will not negotiate)
- Desirable - Desirable (will negociate)
- Desirable - Auto (will negociate)
- Active - Active (will negociate)
- Active - Passive (will negociate)

ETHERCHANNEL LOAD BALANCING

- Available load balancing methods are per-platform as
  - source and destination mac address
  - source and destination ip address
  - source and destination layer 4
- Balancing method is locally significant and outbound
  - Mismatch on either end is ok
  - Adjustments are based on traffic patters to avoid polarization

LAYER 2 VS LAYER 3 ETHERCHANNEL

- LAG is independent of the port mode: access, trunk, tunnel, layer3 (no swithport) , etc
- Members ang LAG interface must agree on parameters
- Both members and LAG are layer 3 or layer 2 but no mix

COMMANDS

- channel-group (number) mode (mode)