Juniper JUNOSE 11.1.X - LINK LAYER CONFIGURATION 4-7-2010, Configuration Manual

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Ethernet Link Redundancy Overview
You can use 802.3ad Link Aggregation (LAG) to configure Ethernet link redundancy
for Fast Ethernet and Gigabit Ethernet interfaces. Ethernet link redundancy enables
you to protect against physical link failure and account for network topology changes
that redirect network traffic to redundant ports.
The following configurations are available:
■
LAG to LAG—Provides redundancy capabilities for two or more ports that are
assigned to a LAG. One member link is configured as the backup interface for
all other ports in the LAG bundle (1:N). Traffic is not forwarded over the backup
member interface; it is disabled until it takes over for an active member interface.
■
LAG to non-LAG—Provides redundancy capabilities when redundant ports are
connected to a bridged network that has Rapid Spanning Tree Protocol (RSTP)
controlling the topology. This configuration supports only two links in the LAG.
For information about the modules that support link aggregation, see ERX Module
Guide, Appendix A, Module Protocol Support and E120 and E320 Module Guide, Appendix
A, IOA Protocol Support .
Ethernet Link Redundancy Configuration Models
The link connections determine the configuration model for link redundancy. The
following connection types are available:
■
Single-homed—Connections are between the local Ethernet interface and a single
remote device. When the peer is also configured with LAG, LACP can be used
to control link access.
■
Dual-homed—Connections are between two separate, uncoordinated remote
devices. The remote interfaces can be on the same module or on separate
hardware. If LAG is not configured on the peers, LACP cannot be used to select
ports; other protocols such as RSTP can be used.
The type of hardware used for connections further characterizes the single-homed
and dual-homed configuration models. The following hardware types are available:
■
Homogeneous—Remote interface is on another Fast Ethernet or Gigabit Ethernet
port in a back-to-back router configuration of identical hardware and JUNOSe
software versions. Both interfaces support the same redundant cabling and
algorithm. The interfaces can be cabled on the same ports (port 0–port 0, port
1–port 1) or cross-cabled (port 0–port 1, port 1–port 0).
■
Heterogeneous—Remote interface is on a different type of hardware that might
or might not support redundant cabling, or on the same type of equipment with
different software versions. For example, a heterogeneous configuration can
include an ES2-S1 GE-4 IOA and an ES2-S1 GE-8 IOA on the E320 router, or an
E Series router operating JUNOSe software connected to another vendor’s router
and software.
Ethernet Link Redundancy Overview
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Chapter 6: Configuring 802.3ad Link Aggregation and Link Redundancy