Link Aggregation Control Protocol

Kashif Latif

Understanding the Link Aggregation Control Protocol

O JUNOS Software supports the Link Aggregation Control Protocol (LACP), which is a subcomponent of IEEE 802.3ad. LACP provides additional functionality for LAGs (Link Aggregation Groups).

O IEEE 802.3 is a working group and a collection of IEEE standards produced by the working group defining the physical layer and data link layer's media access control (MAC) of wired Ethernet.

Working of LACPO LACP provides a standardized means

for exchanging information between partner systems on a link to allow their link aggregation control instances to reach agreement on the identity of the LAG to which the link belongs, and then to move the link to that LAG, and to enable the transmission and reception processes for the link to function in an orderly manner.

Switch ServerNetwork Interface Cards

Example O When LACP is not enabled, a local

LAG might attempt to transmit packets to a remote individual interface, which causes the communication to fail. (An individual interface is a non-aggregatable interface.) 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.

Supported DeviceO LACP does not support automatic

configuration on SRX3000 and SRX5000 line devices, but partner systems are allowed to perform automatic configuration.

O When an SRX3000 or SRX5000 line device is connected to a fully 802.3ad-compliant partner system, static configuration of LAGs is initiated on the SRX3000 and SRX5000 line device side, and static configuration is not needed on the partner side.

Deployments of LACP

O LACP is supported in standalone deployments, where aggregated Ethernet interfaces are supported, and in chassis cluster deployments, where aggregated Ethernet interfaces and redundant Ethernet interfaces are supported simultaneously.

Understanding LACP in Chassis Cluster Mode

O LACP maintains a point-to-point LAG. Any port connected to the third point is denied. However, a redundant Ethernet interface does connect to two different systems or two remote aggregated Ethernet interfaces by design. To support LACP on both redundant Ethernet interface active and standby links, a redundant Ethernet interface can be modeled to consist of two sub-LAGs, where all active links form an active sub-LAG and all standby links form a standby sub-LAG.

O The total number of active and standby links is limited to 16 (8 active and 8 standby).

Hitless FailoverO With LACP, it is essential for the redundant

Ethernet interface to support hitless failover between the active and standby links in normal operation. The term hitless means that the redundant Ethernet interface state remains up during failover.

O To support hitless failover, the LACP state on the redundant Ethernet interface standby links must be collecting and distributing before failover occurs.

Configuring LACP on Stand-Alone Devices

O LACP is enabled by setting the mode to either passive or active. If the actor and partner are both in passive mode, they do not exchange link aggregation control PDUs (Process Data Units), which results in the aggregated Ethernet links not coming up.

O If either the actor or partner is active, they exchange link aggregation control PDUs.

CLI Configuration

To set the LACP mode to passive for ae0:[edit interfaces]user@host# set ae0 aggregated-ether-options lacp passive

To set the LACP mode to active for ae0:[edit interfaces]user@host# set ae0 aggregated-ether-options lacp active

Configuring Transmit Interval

O You configure the interval at which the interfaces on the remote side of the link transmit link aggregation control PDUs by configuring the periodic statement on the interfaces on the local side.

O It is the configuration on the local side that specifies the behavior of the remote side. That is, the remote side transmits link aggregation control PDUs at the specified interval.

O The interval can be fast (every second) or slow (every 30 seconds).

CLI Configuration

To configure the interval to be every 30 seconds:[edit interfacesuser@host# set ae0 aggregated-ether-options lacp periodic slow

Configuring LACP on Chassis Clusters

O We can configure LACP on a redundant Ethernet interface by setting the LACP mode for the parent link with the lacp statement.

O The LACP mode can be off (the default), active, or passive.

CLI ConfigurationTo set the LACP mode to passive for reth0:{primary:node1} [edit interfaces]user@host# set reth0 redundant-ether-options lacp passive

To set the LACP mode to active for reth0:{primary:node1} [edit interfacesuser@host# set reth0 redundant-ether-options lacp active

Configuring Transmit Interval

To configure the interval to be every 30 seconds:[edit interfaces]user@host# set reth0 redundant-ether-options lacp periodic slow

Thank You…!

Kashif Latif