Etherchannel - LACP (Link Aggregation Control Protocol)

Quick reminders;

• EtherChannel mode ON will bundle interfaces irrespective of the configuration of the interfaces on the opposite side of the link.
  

Keywords;

• LACP
• LAG
• Port-channel
• Bandwidth aggregation
• Static Etherchannel – Mode ON
• Dynamically negotiate – Mode Active
• Dynamically negotiate – Mode Passive
• Port priority value
• LACP system ID
• Decision Maker or Master switch
• LACP system priority value

Things i learned in this lab in regards to LACP;

• Member port = Physical interface that is part of an EtherChannel group (Port-Channel).
• LACP ⇒ Link Aggregation Control Protocol.
• LACP uses 3 methods to bundle ports;
  • 2 x Dynamic negotiation = Auto-negotiate and form an Etherchannel group.
  • Mode – Active = Attempt to negotiate with a desire to form an Etherchannel bundle and require the neighboring switch to be in LACP mode Active or Passive.
  • Mode – Passive = Will not attempt to negotiate unless the neighboring protocol is also LACP and mode Active.
  • 1 x Static = Force and bundle physical ports into an Etherchannel group.
  • Mode – ON
• LACP is one of two LAG (Link Aggregation Protocol) widely used in networking today.
• LACP is an IEEE standard (802.3ad) and can be used with a wide variety of vendor switches (L2 and L3).
  • This includes Cisco devices which previously only supported their proprietary equivalent of LAG called Etherchannel and used the PAgP – Port aggregation Protocol.
• You can force a single switch to bundle physical ports into an Etherchannel using the static (Manual) method – Mode ON.
  • However, this is not suggested because it will lead to misconfiguration by having the neighboring switch without an Etherchannel configuration.
• To pair two switches and bundle their respective physical ports into an Etherchannel Port-Channel, you will have to;
  • Shutdown the Interfaces intended for the Etherchannel configuration on both switches.
  • Bundle the interfaces using the static method – Mode ON.
  • Turn on the interfaces.
• The LACP system ID is the combination of LACP system priority value and the MAC address. Think of this as the “Decision-maker” or the “Master” switch.
  • Only 1 switch can be a Decision-Maker in an LACP.
    • This is determined using the switch’s priority value also known as system-priority value.
    • The default system-priority value is 32768.
      • You can manipulate/alter this using the Global config command ⇒Lacp system-priority number.
      • Ex: SW1(config)#lacp system-priority 100.
    • The tiebreaker ⇒ The lowest MAC address between the two switches in an LACP configuration.
• LACP port identifier ⇒ uses port priority value with the port number to form the port identifier.
  • LACP uses the port priority to decide which ports should be put in STANDBY mode when there is a limitation that prevents all compatible ports from aggregating (bundling) and which ports should be put into ACTIVE mode.
  • The default port priority value is 32768.
  • The port priority value can range anywhere from 1 to 65535.
  • The lower the port priority value – the preferred and therefore will be selected to be included in the “Active” links of an LACP. Therefore, a higher port priority value means a lower priority for LACP.
  • This port-priority value helps to identify which ports are active and bundled in an EtherChannel and which ports are Hot Standby and bundled in an EtherChannel.
    • Lower port priority value ⇒ Higher priority for LACP and therefore will be bundled in an Etherchannel (aka be associated within the port-channel group) and become part of the Active links.
    • Higher port priority value ⇒ Lower priority for LACP, therefore become bundled but delegated to a backup role – Hot Standby. The only time these ports become used is whenever an Active and bundled member port fails or has configuration errors, the Hot Standby member port will become active.

SPANNING-TREE CONSIDERATIONS WHEN USING ETHERCHANNEL

• Before Etherchannel is used, using more than 1 link between two switches can create what we call — spanning-tree loop or a layer 2 loop.
• Layer 2 loop is a major problem and cause your switch to become overwhelmed because of its CPU overworking to process all the frames it receives from the layer 2 loop.