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
- Access Network Redundancy Model

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)