Multipoint Layer 2 Services Overview; Bridge Domain - Cisco ASR 9000 Series Configuration Manuallines

Multipoint Layer 2 Services Overview

Multipoint Layer 2 Services Overview
Multipoint Layer 2 Services enable geographically separated local-area network (LAN) segments to be
interconnected as a single bridged domain over an MPLS network. The full functions of the traditional LAN
such as MAC address learning, aging, and switching are emulated across all the remotely connected LAN
segments that are part of a single bridged domain.
Some of the components present in a Multipoint Layer 2 Services network are described in these sections.
Note Multipoint Layer 2 services are also called as Virtual Private LAN Services.

Bridge Domain

The native bridge domain refers to a Layer 2 broadcast domain consisting of a set of physical or virtual ports
(including VFI). Data frames are switched within a bridge domain based on the destination MAC address.
Multicast, broadcast, and unknown destination unicast frames are flooded within the bridge domain. In addition,
the source MAC address learning is performed on all incoming frames on a bridge domain. A learned address
is aged out. Incoming frames are mapped to a bridge domain, based on either the ingress port or a combination
of both an ingress port and a MAC header field.
By default, split horizon is enabled for pseudowires under the same VFI. However, in the default configuration,
split horizon is not enabled on the attachment circuits (interfaces or pseudowires).
Flood Optimization
A Cisco ASR 9000 Series Router, while bridging traffic in a bridge domain, minimizes the amount of traffic
that floods unnecessarily. The Flood Optimization feature accomplishes this functionality. However, in certain
failure recovery scenarios, extra flooding is actually desirable in order to prevent traffic loss. Traffic loss
occurs during a temporary interval when one of the bridge port links becomes inactive, and a standby link
replaces it.
In some configurations, optimizations to minimize traffic flooding is achieved at the expense of traffic loss
during the short interval in which one of the bridge's links fails, and a standby link replaces it. Therefore,
Flood Optimization can be configured in different modes to specify a particular flooding behavior suitable
for your configuration.
These flood optimization modes can be configured:
Bandwidth Optimization Mode
Flooded traffic is sent only to the line cards on which a bridge port or pseudowire that is attached to the bridge
domain resides. This is the default mode.
Convergence Mode
Flooded traffic is sent to all line cards in the system. Traffic is flooded regardless of whether they have a
bridge port or a pseudowire that is attached to the bridge domain. If there are multiple Equal Cost MPLS Paths
(ECMPs) attached to that bridge domain, traffic is flooded to all ECMPs.
The purpose of Convergence Mode is to ensure that an absolute minimum amount of traffic is lost during the
short interval of a bridge link change due to a failure.
L2VPN and Ethernet Services Configuration Guide for Cisco ASR 9000 Series Routers, IOS XR Release 6.3.x
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Implementing Multipoint Layer 2 Services