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Understanding Link Aggregation and Link Aggregation Control Protocol in a Junos Fusion


Link Aggregation in Junos Fusion

Link aggregation is used to aggregate Ethernet interfaces between two devices. The aggregated Ethernet interfaces that participate in a link aggregation group (LAG) are called member links. Because a LAG is composed of multiple member links, even if one member link fails, the LAG continues to carry traffic over the remaining links.

Link Aggregation Control Protocol in Junos Fusion

Link Aggregation Contol Protocol (LACP) is one method of bundling several physical interfaces to form one logical aggregated Ethernet interface. LACP is a subcomponent of the IEEE 802.3ad standard and is used as a discovery protocol. The LACP mode can be active or passive. The transmitting link is known as the actor, and the receiving link is known as the partner. If the actor and partner are both in passive mode, they do not exchange LACP packets, and the aggregated Ethernet links do not come up. If either the actor or partner is active, they do exchange LACP packets. By default, LACP is in passive mode on aggregated Ethernet interfaces. To initiate transmission of LACP packets and response to LACP packets, you must enable LACP active mode. You can configure Ethernet links to actively transmit protocol data units (PDUs), or you can configure the links to passively transmit them, sending out LACP PDUs only when they receive them from another link. You can configure both VLAN-tagged and untagged aggregated Ethernet interfaces without LACP enabled. LACP is defined in IEEE 802.3ad, Aggregation of Multiple Link Segments.

LACP was designed to achieve the following:

  • Automatic addition and deletion of individual links to the LAG without user intervention.

  • Link monitoring to check whether both ends of the bundle are connected to the correct group.

The satellite devices provide network interfaces that send and receive network traffic and process the periodic transmission of LACP packets. You can include extended ports (physical interface on a satellite device that provides a connection to servers or endpoints) or local ports in LAGs and MC-LAGs, but not both.

When a dual-homed end device is deployed with Junos Fusion, the network interface cards form a LAG with the Junos Fusion. During a Junos Fusion upgrade, the end device 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 force-up statement to configure an interface when the peer has limited LACP capability. The interface selects the associated LAG by default, whether the LACP mode is active or passive. 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.

Configuring Link Aggregation and LACP in Junos Fusion

  1. Create a logical aggregated Ethernet interface.

  2. Define the parameters associated with the logical aggregated Ethernet interface, such as a logical unit, interface properties, and Link Aggregation Control Protocol (LACP).

  3. Define the member links to be contained within the aggregated Ethernet interface—for example, two local 10-Gigabit Ethernet interfaces on the aggregation device or two extended ports on the aggregation device.

    • LAGs and MC-LAGs cannot include a mix of extended ports and local ports on the aggregation device.

    • LAGs can span across multiple satellite devices in Junos Fusion Provider Edge.

    • LAGs cannot contain both single-homed and multihomed members.

    • Existing restrictions that apply to LAGs and MC-LAGs also apply to LAGs and MC-LAGs that include extended ports.

  4. Configure LACP for link detection.

Software and Hardware Guidelines when Configuring Link Aggregation and LACP in Junos Fusion

Keep in mind these hardware and software guidelines:

  • Up to 1750 LAGs are supported in Junos Fusion Provider Edge and Junos Fusion Enterprise, and the LAGs are numbered from ae0 through ae4091.

  • Up to 16 members are supported in a LAG in Junos Fusion Provider Edge and Junos Fusion Enterprise.

  • Configure the LAG on both sides of the link.

  • The interfaces on either side of the link must be set to the same speed and be in full-duplex mode.

  • Configure LACP for dual-homed extended ports identically on both of the aggregation devices; otherwise LACP will not be in a forwarding state.