Bundle Ethernet Multichassis

Introduction

Multichassis Link Aggregation (MC-LAG) is an ASR9k link aggregation between two different chassis. This document provides an overview of MLAG.

MC-LAG Overview

  • MC-LAG allows for a third device to connect a Bundle interface to two different ASR9K chassis.
  • It provides a link and device-level redundancy.
  • Only one device performs the forwarding (Active/Standby).
  • Cisco nomenclature refers to the CE at Dual-Homed-Device (DHD) and the two PEs configured with MC-LAG as the **Point of Attachment (POA).
  • Loss of connectivity between the POAs will lean to a split brains, where both of the devices try to become active.
  • The Interchassis Communication Protocol (ICCP) manages the setup and controls the Redundancy Groups between PEs.
  • There are two main groups of redundancy models Access Network Redundancy Model and Core Network Redundancy Model.
    • Access Network Redundancy Model
      • ICCP Service Multihoming (ICCP-SM)
      • mLACP
      • Pseduo mLACP
    • Core Network Redundancy Model
      • One Way Pseudowire Redundancy
      • Two Way Pseudowire Redundancy
mlag-diagram-overview.jpg

ICCP

  • Control used to manage the Redundancy Groups (RG) between two of the POA chassis.
  • It uses an LDP link between two PEs.
  • The PE can be directly connected or using multiple hops to connect to each other.
  • A PE can be a member of multiple Redundancy Groups.
  • The ICCP protocol operates between the active and the standby POAs, and allows the POAs to coordinate their configuration, determine which POA is active, and trigger a POA to become active.
  • Applications running on the two POAs (mLACP, IGMP snooping, DHCP snooping or ANCP) synchronize their state using ICCP.

mLACP

  • Multichassis Link Aggregation Control Protocol (mLACP)

Configuration

  • Basic configuration of an MC-LAG:
    • Configure the ICCP redundancy group for the POA.
    • Define the redundant neighbor IP address (LDP Router-ID)

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