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IEEE 802.3ad Link Aggregation and LACP

Abstract: This article mainly introduces the concept of link aggregation and the difference between link aggregation and EtherChannel.

Description:

IEEE 802.3ad is a standard method for performing link aggregation. Conceptually, aggregating multiple Ethernet adapters into a single virtual adapter is the same function as EtherChannel, providing higher bandwidth to prevent failures. For example, ent0 and ent1 can be aggregated into an IEEE 802.3ad link aggregation called ent3; interface en3 is then configured with an IP address. The system considers these aggregated adapters as one adapter. Therefore, their IP can be configured just like on any Ethernet adapter.

Like Ethernet, IEEE 802.3ad requires switch support. Unlike Ethernet Channel, however, the switch does not require manual configuration to know which ports belong to the same aggregation.

The advantage of using IEEE 802.3ad Link Aggregation instead of Ethernet Channel is that it automatically creates link aggregation in the switch, and it allows you to use switches that support IEEE 802.3ad standards but do not support Ethernet Channel.

In IEEE 802.3ad, Link Aggregation Control Protocol (LACP) automatically tells switches which ports should be aggregated. After IEEE 802.3ad aggregation is configured, Link Aggregation Control Protocol Data Units (LACPDUs) are exchanged between servers and switches. The LACP informs the switch that the adapter configured in the aggregation should be considered as an adapter on the switch without further user intervention.

While IEEE 802.3ad specifications do not allow users to select adapters to aggregate, AIX implementations allow users to select adapters. According to the rules of the protocol, LACP decides entirely on its own which adapters should be clustered together (by making link aggregation of all adapters using similar link speeds and dual settings). This prevents you from deciding which adapters should stand alone and which should be clustered together. AIX, however, exercises control over how adapters are used, and it never creates links arbitrarily. This is important for managing adapters.

To be able to aggregate adapters (that is, switches will allow them to belong to the same aggregation), they must have the same line speed (for example, all 100 Mbps or 1 Gbps), and they must all be full-duplex. If you try to cluster adapters with different line speeds or different full-duplex modes, you can successfully create aggregations on AIX, but switches may not cluster these adapters. If the switch does not successfully cluster the adapters together, you may notice a decrease in network performance.

According to IEEE 802.3ad specifications, packets destined for the same IP address are sent through the same adapter. Therefore, when operating in 8023ad mode, packets are always distributed in Standard mode, not Round-Robin mode.

Backup adapter functionality is available for IEEE 802.3ad Link Aggregation, just as it is for Ethernet Channel. The backup adapter does not need to be connected to an IEEE 802.3ad enabled switch, but if it is already connected, the backup adapter will still comply with IEEE 802.3ad LACP.

You can also configure IEEE 802.3ad Link Aggregation if the switch supports Ethernet Channel but not IEEE 802.3ad. In that case, you must manually configure the port as an Etherchannel on the switch (just as you would have created a regular Etherchannel). When the mode is set to 8023ad, the aggregation works with Ethernet Channel enabled switches and IEEE 802.3ad enabled switches.

Note:

The procedure for enabling IEEE 802.3ad varies from switch to switch. You should consult the switch documentation to determine which initial steps, if any, must be performed in order to enable LACP in the switch.

precautions

Before configuring IEEE 802.3ad Link Aggregation, consider the following:

1. AIX in IEEE 802.3ad mode implements an officially unsupported "link aggregation" that allows adapters with different line speeds, and you should only aggregate adapters set to the same line speed and set to full duplex. This helps avoid potential problems with configuring Link Aggregation on switches. For more information about what types of aggregation your switch allows, see the switch documentation.

2. If you want to use 10/100 Ethernet adapters in link aggregations on AIX 5.2 with 5200-01 and earlier, you need to enable link polling on those adapters before adding them to the aggregation. Enter smitty chgenet on the command line. Change the Enable Link Polling value to yes and press Enter. Do this for each 10/100 Ethernet adapter you want to add to Link Aggregation.

Link aggregation refers to combining multiple lines between switches or between switches and other devices into a single line. This increases both bandwidth and reliability.

Link aggregation is a technology supported on switches that virtualizes two or more simultaneously connected links between two switches into one link to transmit information.

Link aggregation technology is also known as trunking technology or bonding technology. Its essence is to "combine" several physical links between two devices into a logical data path, which is called an aggregated link, as shown in the figure below. The physical links Link 1, Link2, and Link3 between switches form an aggregated link. The link is logically integrated, and the details of its internal composition and transmission data are transparent to the upper layer services.

The internal physical links complete the task of data transmission and reception together and backup each other. As long as there are still working members, the entire transmission link will not fail. Still using the link aggregation example shown in the previous figure, if Link1 and Link2 fail one after the other, their data tasks will be quickly transferred to Link3, so the connection between the two switches will not be interrupted.

Benefits of Link Aggregation

As can be seen from the above, link aggregation has some significant advantages:

1. Improve link availability

In link aggregation, members backup each other dynamically. When a link breaks, other members can quickly take over. Unlike Spanning Tree Protocol, the process of enabling backup in link aggregation is invisible outside the aggregation, and the process of enabling backup is only within the aggregated link, independent of other links, and the handover can be completed in milliseconds.

2. Increase link capacity

Another obvious advantage of aggregation technology is that it provides users with an economical way to increase link transmission rate. By bundling multiple physical links, users do not have to upgrade existing equipment to obtain a larger bandwidth data link with a capacity equal to the sum of the physical link capacities. The aggregation module distributes traffic to different members according to a certain algorithm to achieve link-level load sharing.

In some cases, link aggregation is even the only way to increase link capacity. For example, when no device on the market can provide a link higher than 10G, the user can aggregate two 10G links to obtain a transmission line with a bandwidth greater than 10G.

3, cheap price, performance close to Gigabit Ethernet.

4, no need to re-wiring, also do not need to consider Gigabit network headache transmission distance limit.

Trunking can bundle any relevant port or cancel the setting at any time, which provides a high degree of flexibility.

6. Trunking can provide Load Balancer capability and system fault tolerance. Because Trunking balances the traffic of each switch port and server interface in real time, once a port fails, it will automatically withdraw the failed port from the Trunking group, and then redistribute the traffic of each Trunking port, thus realizing system fault tolerance.

In addition, in a specific networking environment, the capacity of the transmission line needs to be limited, neither too low to affect the transmission speed nor too high to exceed the processing capacity of the network. However, the prior art only supports the link bandwidth to increase by 10 orders of magnitude, such as 10M, 100M, 1000M, etc. By bundling n physical links together through aggregation, we can get more suitable links with n times bandwidth.

directory

EtherChannel 1

1. Protocol: LACP. 1

1.1LACP mode: ... 1

2. Guidelines for configuring EtherChannel: ... 2

3. EtherChannel Load Balancer... 2

4. EtherChannel vs STP. 2

5. EtherChannel Purpose... 2

6. Other... 2

EtherChannel

Because PAgP is Cisco proprietary, we choose the broader LACP protocol to discuss EtherChannel.

1. Protocol: LACP

LACP (Link Aggregation Control Protocol) is a protocol that implements link dynamic aggregation and uses LACPDU to exchange information with peers.

1.1 LACP mode:

ON: Forces the port to form an EtherChannel, and the other side of the link must also be in ON mode if EtherChannel is to work correctly.

OFF: Causes ports not to form EtherChannels. Ports in this mode do not form EtherChannels.

Passive: Put the port into passive negotiation state, if it can receive LACP packets from the peer, then form an EtherChannel. This mode does not initiate EtherChannel negotiation. This mode is the default mode.

Active: Causes ports to enter an active negotiation state, where configured ports actively send LACP data names to initiate negotiations that can form EtherChannels. This model is generally recommended.

2. Guidelines for configuring EtherChannel:

Cisco switches support up to eight ports to form an EtherChannel, and these ports do not have to be contiguous or in the same module.

All ports within an EtherChannel must use the same protocol (typically the LACP protocol).

All ports within an EtherChannel must have the same speed and duplex mode, otherwise an EtherChannel cannot be formed.

LACP requires that the port only operate in full duplex mode.

All ports in an EtherChannel must be configured into the same VLAN and must have the same trunk mode.

3. EtherChannel Load Balancer

EtherChannel supports source/destination Load Balancer based on Layer 2 MAC, Layer 3 IP, and Layer 4 port numbers, efficiently using existing links. When a link in EtherChannel is down, other links are immediately used to bear the traffic of the link. This in fact makes EtherChannel have the characteristics of link hot backup and improves link redundancy.

4. EtherChannel and STP

STP treats EtherChannel as a single logical port, so that ports in EtherChannel are not blocked by STP, improving the efficiency of link usage.

5. EtherChannel Purpose

Generally, we use EtherChannel to increase the bandwidth of existing links. This method of increasing bandwidth does not need to increase more cost, but only needs to have extra ports. EtherChannel is also commonly referred to as link bundling.

6. other

EtherChannel ports can be used as Layer 2, Layer 3 ports (depending on the physical port), and EtherChannel forms logical ports that have almost all the characteristics of physical ports and can be configured as physical ports.

Static and dynamic convergence of LACP, static is to basket several interfaces together, so that it can not change the combination like dynamic.

Dynamic fluctuations will form new groups as long as they fluctuate, and UNSELETE will be exceeded.

Generally, a group is composed of 4 tuples, but if there is a single interface, it is necessary to mark a group together with the port ID. The logo indicates that it is unique

The master device directly determines which LINK interfaces should belong to SELETE, while the slave device interface priority is inactive.

The LACP protocol is divided into active and passive modes, and the passive mode interface can reduce the consumption of CPU by the LACP protocol.

The dynamic LACP protocol synchronizes the configuration of interfaces, and the VLAN configuration of only one interface is synchronized to other interfaces.

So what really affects them is duplex mode and speed.

Statically configured interfaces are selected in order of preference whether the aggregated interfaces do not require manually defined rates

The LACP protocol is automatically enabled when static aggregation occurs.

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