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352-001 · Question #4

A network designer is working with a company to improve convergence at the Layer 2 control plane and decides to use LACP. Which of these components does LACP use to create the system ID?

The correct answer is A. LACP system priority and switch MAC address. The LACP system ID is an 8-byte value formed by concatenating the 2-byte LACP system priority with the 6-byte switch MAC address, uniquely identifying a device in LACP negotiations.

Layer 2 Control Plane

Question

A network designer is working with a company to improve convergence at the Layer 2 control plane and decides to use LACP. Which of these components does LACP use to create the system ID?

Options

  • ALACP system priority and switch MAC address
  • BLACP port priority and switch MAC address
  • CLACP port priority and port number
  • DLACP system priority and port number

How the community answered

(56 responses)
  • A
    86% (48)
  • B
    9% (5)
  • C
    2% (1)
  • D
    4% (2)

Why each option

The LACP system ID is an 8-byte value formed by concatenating the 2-byte LACP system priority with the 6-byte switch MAC address, uniquely identifying a device in LACP negotiations.

ALACP system priority and switch MAC addressCorrect

LACP constructs the system ID by combining the LACP system priority (2 bytes) and the switch MAC address (6 bytes) into an 8-byte identifier that is advertised in LACPDUs - this value determines which device acts as the controlling system and how port aggregation decisions are made between peers.

BLACP port priority and switch MAC address

LACP port priority is used as part of the port ID in combination with the port number - it operates at the individual port level and is not a component of the system-level identifier.

CLACP port priority and port number

Port priority and port number together form the LACP port ID, which governs individual port selection within an existing aggregate - neither value contributes to the system ID.

DLACP system priority and port number

While LACP system priority is correctly part of the system ID, port number belongs to the port ID structure - combining system priority with port number does not correspond to any valid LACP identifier.

Concept tested: LACP system ID construction using priority and MAC address

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mp_lag/configuration/xe-16/mp-lag-xe-16-book/mp-lag-config.html

Topics

#LACP#system ID#EtherChannel#system priority

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