Juniper JUNOS OS 10.3 - SOFTWARE Manual page 1197

Link Aggregation Control Protocol (LACP)
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Copyright © 2010, Juniper Networks, Inc.
NOTE: The interfaces that are included within a bundle or LAG are sometimes
referred to as member interfaces. Do not confuse this term with member
switches, which refers to Juniper Networks EX4200 Ethernet Switches that
are interconnected as a Virtual Chassis. It is possible to create a LAG that is
composed of member interfaces that are located in different member
switches of a Virtual Chassis.
A LAG creates a single logical point-to-point connection. A typical deployment for a LAG
would be to aggregate trunk links between an access switch and a distribution switch or
customer edge (CE) router.
When LACP is configured, it detects misconfigurations on the local end or the remote
end of the link.
About enabling LACP:
When LACP is not enabled, a local LAG might attempt to transmit packets to a remote
single interface, which causes the communication to fail.
When LACP is enabled, a local LAG cannot transmit packets unless a LAG with LACP
is also configured on the remote end of the link.
By default, Ethernet links do not exchange protocol data units (PDUs), which contain
information about the state of the link. You can configure Ethernet links to actively
transmit PDUs, or you can configure the links to passively transmit them, sending out
LACP PDUs only when they receive them from another link. The transmitting link is known
as the actor and the receiving link is known as the partner.
In a scenario where a dual-homed server is deployed with a switch, the network interface
cards form a LAG with the switch. During a server upgrade, the server may not be able
to exchange LACP PDUs. In such a situation you can configure an interface to be in the
UP state even if no PDUs are exchanged. Use the
interface when the peer has limited LACP capability. The interface selects the associated
LAG by default, whether the switch and peer are both in active or passive mode. When
there are no received PDUs, the partner is considered to be working in the passive mode.
Therefore, LACP PDU transmissions are controlled by the transmitting link.
If the remote end of the LAG link is a security device, LACP might not be supported
because security devices require a deterministic configuration. In this case, do not configure
LACP. All links in the LAG are permanently operational unless the switch detects a link
failure within the Ethernet physical layer or data link layers.
Understanding Virtual Chassis Configurations and Link Aggregation on page 932
Understanding Redundant Trunk Links on EX Series Switches on page 1291
Example: Configuring Aggregated Ethernet High-Speed Uplinks Between a Virtual
Chassis Access Switch and a Virtual Chassis Distribution Switch on page 970
Chapter 50: Interfaces—Overview
statement to configure an
force-up
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