Today we will discuss about Link aggregation, This is very important topic in switching. This is many times used in Enterprises network for trunking. Basically this will help to bind several physical links together to form a logical link and it can be used to increase link bandwidth for trunk. Meanwhile, each aggregation member link can achieve dynamic backup with each other to provide higher connection reliability.
This section describes the concept of the link aggregation. Main contents:
- Terms of the link aggregation
- Functions of the link aggregation
- LACP protocol
Terms of the Link Aggregation
Link aggregation: multiple physical links are bound together to form a logical link, which expands the link bandwidth. At the same time, the member links of the aggregation are dynamic backup mutually. It provides higher reliability.
- LAC: Link Aggregation Control
- LACP: Link Aggregation Control Protocol, defined in IEEE802.3ad.
- LACPDU: Link Aggregation Control Protocol Data Unit.
- LAG: Link Aggregation Group.
- LAG ID: Link Aggregation Group Identifier.
- Key: 16-bit integer variable, for describing the aggregation capability of a port. It is composed of rate, duplex, and administrative key (aggregation group ID).
- Administrative Key: The key used by the administrator for setting.
- Operational Key: The key reflecting the port aggregation capability.
Functions of the Link Aggregation
The link aggregation is a aggregation group composed of multiple ports. The upper layer entities using the link aggregation service regard the multiple physical links in the same aggregation group as a logical link. The function of the link aggregation is to share the in/out load in each member port to increase the link bandwidth. At the same time, member ports of the aggregation group are dynamic backup mutually. It provides higher reliability.
LACP Protocol
IEEE802.3ad-based LACP is a protocol for implementing the link dynamic aggregation. The LACP protocol communicates with the opposite end through the Link Aggregation Control Protocol Data Unit (LACPDU). After the LACP protocol of a port is enabled, the port advertises the system priority, system MAC address, port priority, port number, and the operation key to the opposite end by sending LACPDU. After the opposite end receives the information, compare the information with the information saved in other ports to select port to aggregate. As a result, the two parties can agree with each other on joining or exiting a dynamic aggregation group. The operation key is a configuration combination generated by the LACP protocol according to the port configuration (rate, duplex, administrative key).
Classification of Link Aggregation
The link aggregation can be classified into two types according to the aggregation mode:
- Manual aggregation
- LACP protocol aggregation
Below are configuration examples for both modes.
Topology
LAC configuration
As figure above, ports 0/1-0/3 between two switches connect with each other. Local switch switch1 aggregates peer switch switch2; three ports of each side participate in the aggregation. Suppose that the numbers of the ports that participate in the aggregation at the two sides are all 0/1-0/3.
Mode 1: Manual Aggregation
switch1 configuration:
| Command | Description |
| switch (config)#link-aggregation 1 mode manual | Create manual aggregation group 1 |
| switch (config)#port 0/1-0/3 | Enter the port mode |
| switch (config-port-range)#link-aggregation 1 manual | Add a port into aggregation group in manual mode |
switch2 configuration:
| Command | Description |
| switch (config)#link-aggregation 1 mode manual | Create manual aggregation group 1 |
| switch (config)#port 0/1-0/3 | Enter the port mode |
| switch (config-port-range)#link-aggregation 1 manual | Add a port into an aggregation group in manual mode |
Mode 2: Protocol Aggregation
switch1 configuration
| Command | Description |
| switch (config)#link-aggregation 1 mode lacp | Create protocol aggregation group 1 |
| switch (config)#port 0/1-0/3 | Enter the port mode |
| switch (config-port-range)#link-aggregation 1 active | Add a port into an aggregation group in protocol mode |
switch2 configuration:
| Command | Description |
| switch (config)#link-aggregation 1 mode lacp | Create protocol aggregation group 1 |
| switch (config)#port 0/1-0/3 | Enter the port mode |
| switch (config-port-range)#link-aggregation 1 active | Add a port into an aggregation group in protocol mode |
Monitoring Commands
View Commands:
| Command | Description |
| show link-aggregation group [agg-id] | Display the aggregation information of a specified aggregation group |
| show link-aggregation port [port_no] | Display the aggregation information of a port |
Debugging Commands
| Command | Description |
| (no) debug lac [pdu [rx|tx] | machine | event ] [port port-no] | Enable the debugging switch of the information about link aggregating process. |
Hope this information will help you for understanding of Link aggregation concept and configuration in Maipu Switches for Cisco it’s same. Cisco is having PAGP propriety protocol for Link aggregation.
Port Aggregation Protocol (PAGP)
- Cisco Proprietary
- Port Modes : Auto , Desirable , On
If Both side you set as a Auto mode then it will not become Ether Channel
- Auto Means : It will say u want to be a Ether channel
- Desirable Mode: It will u r Ether channel the I will be.
- On: No Negotiating -- He will be only Ether channel and Destination Switch should be configured as a Ether channel. [ Better One ]
PagP Configuration Example :-
SwitchA(config)# int range fastethernet 0/23 - 24
SwitchA(config- if)# channel-protocol PagP
SwitchA(config- if)# channel-group 1 mode desirable
SwitchB(config)# int range fastethernet 0/23 - 24
SwitchB(config- if)# channel-protocol PagP
SwitchB(config- if)# channel-group 1 mode auto
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