Introduction to Port Channels and LACP

Today I am going to talk about the LACP protocol or people also knew this as port-channel or ether-channel. This topic is basically based on the Arista Networks switches. I will discuss the basics of port channel and then we will have the configurations on the switches.

What is Port Channel ? when and where it is used ?
A port channel is a communication link between two switches that consists of matching channel group interfaces on each switch. A port channel is also referred to as a Link Aggregation Group (LAG). Port channels combine the bandwidth of multiple Ethernet ports into a single logical link. 
A channel group is a collection of Ethernet interfaces on a single switch. 

Fig 1.1- LACP between Cisco and HP Switches
A port channel interface is a virtual interface that consists of a corresponding channel group and connects to a compatible interface on another switch to form a port channel. Port channel interfaces can be configured and used in a manner similar to Ethernet interfaces. Port channel interfaces are configurable as layer 2 interfaces, layer 3 (routable) interfaces, and VLAN members. Most Ethernet interface configuration options are available to port channel interfaces. 

What are the various types of LACP ?
Well in this article we will discuss two kinds of LACP protocols, one is static and other is dynamic LACP. Below are the explanation of both the LACP models

In static mode, switches create port channels without awareness of their partner’s port channels. Packets may drop when port channel static aggregate configurations differ between switches. The switch aggregates static links without LACP negotiation. The switches do not send LACP packets nor process inbound LACP packets. 

In dynamic mode, Link Aggregation Groups are aware of their partners’ port channel states. Interfaces configured as dynamic LAGs are designated as active or passive. Active interfaces send LACP Protocol Data Units (LACP PDUs) at a rate of one per second when forming a channel with an interface on the peer switch. An aggregate forms if the peer runs LACP in active or passive mode. Passive interfaces only send LACP PDUs in response to PDUs received from the partner. The partner switch must be in active mode and initiates negotiation by sending an LACP packet. The passive mode switch receives and responds to the packet to form a LAG. 

What are the port configuration on Switch 1 and Switch 2 in order to achieve LACP negotiation ?
Well for that below table describe the LACP negotiation mode successful on the switches.

Fig 1.2- LACP Switch modes
LACP in Arista Networks
So if we talk about the Arista Networks, Arista switches will optimize traffic throughput by using MAC, IP addressing and services fields to effectively load share traffic across aggregated links. Managers can configure multiple ports into a logical port channel, either statically or dynamically through the IEEE Link Aggregation Control Protocol (LACP). 

Various negotiation modes are supported to accommodate any variety of configurations or peripheral requirements, including LACP fallback to support devices that need simple network connectivity to retrieve images or configurations prior to engaging port channel aggregation modes. 

Arista’s Multi-chassis Link Aggregation protocol (MLAG) supports LAGs across paired Arista switches to provide both link aggregation and active/active redundancy.

Let's talk about the configuration part of LACP between the two switches

Step 1 : Creating a Channel Group
xproute(config)#interface ethernet 1-2 
xproute(config-if-Et1-2)#channel-group 10 mode active 

Step 2: Adding and Removing an interface to Channel Group
xproute(config)#interface ethernet 7-10 
xproute(config-if-Et7-10)#channel-group 10 mode active 

xproute(config)#interface ethernet 8 
xproute(config-if-Et8)#no channel-group 

Step 3: Configuring and creating a Port Channel interface
ttlbits(config)#interface port-channel 8 

Step 4: Configuring LACP mode
xproute(config)#interface ethernet 1-2 
xproute(config-if-Et1-2)#channel-group 10 mode active 

Step 5: Configuring System and Port Priority with LACP Packet Transmission Rate 
xproute(config)#lacp system-priority 8192 
xproute(config-if-Et1)#lacp port-priority 4096 
xproute(config-if-Et4)#lacp rate fast 

Step 6: Configuring LACP Fallback 
xproute(config)#interface port-channel 13 >>>>> Port Channel taken just for an example

xproute(config-if-Po13)#port-channel lacp fallback static 
xproute(config-if-Po13)#port-channel lacp fallback timeout 100 
xproute(config-if-Po13)#show active
interface Port-Channel13
port-channel lacp fallback static
port-channel lacp fallback timeout 100

xproute(config)#interface port-channel 17  >>>>> Port Channel taken just for an example
xproute(config-if-Po17)#port-channel lacp fallback individual 
xproute(config-if-Po17)#port-channel lacp fallback timeout 50 
xproute(config-if-Po17)#show activeinterface Port-Channel17
port-channel lacp fallback individual
port-channel lacp fallback timeout 50

Step 7: Configuring Minimum Links 
switch(config-if-Po5)#port-channel min-links 4 

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