Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?

 
ON THIS PAGE
 

Aggregated Ethernet Interfaces Overview

Learn about aggregated Ethernet interfaces, LACP, and LAG.

Overview

IEEE 802.3ad link aggregation enables you to group Ethernet interfaces to form a single link layer interface, also known as a link aggregation group (LAG) or bundle.

Aggregating multiple links between physical interfaces creates a single logical point-to-point trunk link or a LAG. The LAG balances traffic across the member links within an aggregated Ethernet bundle and effectively increases the uplink bandwidth. Another advantage of link aggregation is increased availability, because the LAG is composed of multiple member links. If one member link fails, the LAG continues to carry traffic over the remaining links.

You can configure a mixed rate of link speeds for the aggregated Ethernet bundle. Link speeds of 10GbE, 40GbE, and 100GbE are supported. Load balancing does not work if you configure link speeds that are not supported.

Use Aggregated Ethernet interface to confirm platform and release support for specific features.

You can configure port channel using different SFP models between two endpoints keeping the same bandwidth.

For example:

switch 1 gig0/1 (SFP-10G-SR-S) --------- MX 1 gig0/1 (SFP-10G-SR-S)

switch 1 gig0/2 (SFP-10G-LR-S) --------- MX 1 gig0/2 (SFP-10G-LR-S)

Link Aggregation Control Protocol (LACP) is a subcomponent of the IEEE 802.3ad standard and is used as a discovery protocol.

To ensure load balancing across the aggregated Ethernet (AE) interfaces on a redundant server Node group, the members of the AE must be equally distributed across the redundant server Node group.

During a network Node group switchover, traffic might be dropped for a few seconds.

Link Aggregation Group (LAG)

You configure a LAG by specifying the link number as a physical device and then associating a set of interfaces (ports) with the link. All the interfaces must have the same speed and be in full-duplex mode. Juniper Networks Junos operating system (Junos OS) for EX Series Ethernet Switches assigns a unique ID and port priority to each interface. The ID and priority are not configurable.

The number of interfaces that can be grouped into a LAG and the total number of LAGs supported on a switch varies according to switch model. Table 1 lists the EX Series switches and the maximum number of interfaces per LAG and the maximum number of LAGs they support.

LAGs with member links of different interface types, for example, ge and mge are not supported on multirate switches.

For Junos OS Evolved, the software does not impose a limit on the maximum number of aex in a mixed-rate aggregated Ethernet bundle. All child logical interfaces belong to the same aggregated Ethernet physical interface and share the same selector. So, much less load-balance memory and mixed-rate aex configurations should go through even if number exceeds 64 logical interfaces.

Table 1: Maximum Interfaces per LAG and Maximum LAGs per Switch (EX Series Switches)

Switch

Maximum Interfaces per LAG

Maximum LAGs

EX4100-F Virtual Chassis 8 128

EX4200 and EX4200 Virtual Chassis

8

111

EX4300 and EX4300 Virtual Chassis

16

128
EX4400 16 128

EX4600

32

128
EX4650 Virtual Chassis 64 72

EX6200

8

111

EX9200

64

150
Table 2: Maximum Interfaces per LAG and Maximum LAGs per Switch (QFX Series Switches)

Switch

Maximum Interfaces per LAG

Maximum LAGs

QFX5100

64

96

QFX5110

64

96

QFX5120

64

72
QFX5130 64 128

QFX5200

64

128

QFX5700

128

144

QFX10002

64

150

QFX10008

64

1000

QFX10016

64

1000

On QFX Series switches, if you try to commit a configuration containing more than 64 Ethernet interfaces in a LAG, you receive an error message. The error message says that the group limit of 64 has been exceeded and the configuration checkout has failed.

To create a LAG:

  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 10-Gigabit Ethernet interfaces.

  4. Configure LACP for link detection.

Keep in mind these hardware and software guidelines:

  • For Junos OS Evolved, when a new interface is added as a member to the aggregated Ethernet bundle, a link flap event is generated. When you add an interface to the bundle, the physical interface is deleted as a regular interface and then added back as a member. During this time, the details of the physical interface are lost.

  • Up to 32 Ethernet interfaces can be grouped to form a LAG on a redundant server Node group, a server Node group, and a network Node group on a QFabric system. Up to 48 LAGs are supported on redundant server Node groups and server Node groups on a QFabric system, and up to 128 LAGs are supported on network Node groups on a QFabric system. You can configure LAGs across Node devices in redundant server Node groups, server Node groups, and network Node groups.

    On a Qfabric system, if you try to commit a configuration containing more than 32 Ethernet interfaces in a LAG, you will receive an error message saying that the group limit of 32 has been exceeded, and the configuration checkout has failed.

  • The LAG must be configured 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.

    Junos OS assigns a unique ID and port priority to each port. The ID and priority are not configurable.

  • QFabric systems support a special LAG called an FCoE LAG, which enables you to transport FCoE traffic and regular Ethernet traffic (traffic that is not FCoE traffic) across the same link aggregation bundle. Standard LAGs use a hashing algorithm to determine the physical link used for transmission. Thus, communication between two devices might use different physical links in the LAG for different transmissions. An FCoE LAG ensures that FCoE traffic uses the same physical link in the LAG for requests and replies. This preserves the virtual point-to-point link between the FCoE device converged network adapter (CNA) and the FC SAN switch across a QFabric system Node device. An FCoE LAG does not provide load balancing or link redundancy for FCoE traffic. However, regular Ethernet traffic uses the standard hashing algorithm and receives the usual LAG benefits of load balancing and link redundancy in an FCoE LAG. See Understanding FCoE LAGs for more information.

Link Aggregation Control Protocol (LACP)

LACP is one method of bundling several physical interfaces to form one logical aggregated Ethernet interface. By default, Ethernet links do not exchange LACP protocol data units (PDUs), which contain information about the state of the link. You can configure Ethernet links to actively transmit LACP PDUs, or you can configure the links to passively transmit them, sending out LACP PDUs only when the Ethernet link receives them from the remote end. 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 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.

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 might 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 switch and peer are both in active or passive mode. When PDUs are not received, 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.

When LACP is configured, it detects misconfigurations on the local end or the remote end of the link. Thus, LACP can help prevent communication failure:

  • 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.