Administrator Guide

998 Link Aggregation
Multi-Switch LAG (MLAG)
Overview
In a typical layer-2 network, the Spanning Tree Protocol (STP) is deployed to
avoid packet storms due to loops in the network. To perform this function,
STP sets ports into either a forwarding state or a blocking state. Ports in the
blocking state do not carry traffic. In the case of a topology change, STP re-
converges to a new loop-free network and updates the port states. STP is
relatively successful mitigating packet storms in the network, but redundant
links in the network are blocked from carrying traffic by the spanning tree
protocol.
In some network deployments, redundant links between two switches are
bundled together in a Link Aggregation Group (LAG) and appear as a single
link in the spanning tree topology. The advantage is that all LAG member
links can be in the forwarding state and a link failure can be recovered in
milliseconds. This allows the bandwidth on the redundant links to be utilized.
However, LAGs are limited to connecting multiple links between two partner
switches, which leaves the switch as a single point of failure in the topology.
Dell Networking MLAG extends the LAG bandwidth advantage across
multiple Dell Networking N-Series switches connected to a LAG partner
device. The LAG partner device is unaware that it is connected over a LAG to
two peer Dell Networking N-Series switches; instead, the two switches appear
as a single switch with a single MAC address to the partner. All links can carry
data traffic across a physically diverse topology and in the case of a link or
switch failure, traffic can continue to flow with minimal disruption.
NOTE: This feature is not available on the Dell Networking N1500 Series
switches.