Why Dynamic Etherchannel Over Static Static Configuration ?

[GabrielART]

Hello ladies and gents, 

This might be an easy question for some of you, but I am still trying to see the benefit of dynamic Etherchannel configuration over static configuration. The amount of line commands are the same as shown in the example below, so there is no benefit on the configuration part, other than load-balancing and link failures. Thanks.

Example of comparing the amount of lines necessary to configure dynamic and static Etherchannel. 

Example 1 - LACP Ethernchannel: 

SW1(config)#interface range f0/23 - 24

SW1(config-if-range)#channel-group 1  mode active

SW1(config-if-range)#exit

SW1(config)#inter port-channel 1

SW1(config-if)#description Link to SW2

SW1(config-if)#switchport mode trunk

SW1(config-if)#switchport trunk native vlan 199

SW2(config)#inter range f0/23 - 24

SW2(config-if-range)#channel-group 1 mode active

SW2(config-if-range)#exit

SW2(config)#inter port-channel 1

SW2(config-if)#description Link to SW1

SW2(config-if)#switchport mode trunk

SW2(config-if)#switchport trunk native vlan 199

Example 2 - Static Etherchannel: 

SW1(config)#inter range g0/1 - 2

SW1(config-if-range)#channel-group 3 mode on

SW1(config-if-range)#exit

SW1(config)#inter port-channel 3

SW1(config-if)#description Link to SW2

SW1(config-if)#switchport mode trunk

SW1(config-if)#switchport trunk native vlan 199

SW2(config)#inter range g0/1 - 2

SW2(config-if-range)#channel-group 3 mode on

SW2(config-if-range)#exit)

SW2(config)#inter port-channel 3

SW2(config-if)#description Link to SW1

SW2(config-if)#switchport mode trunk

SW2(config-if)#switchport trunk native vlan 199

[Flavio Miranda]

@GabrielART 

 We have other discussion related that can be usefull for you

https://community.cisco.com/t5/switching/static-and-dynamic-ether-channel/td-p/2217335

[GabrielART]

Thank Flavio for the feedback. Coincidently, I had already read through that article before posting this one. The thing is, technicians always mentioned that it is better to use PAgP, or LACP to minimize the errors when configuring Etherchannel, and they also say that is the benefit of using a dynamic protocol over a static, but as shown on my previous example, both types of configuration yield the same amount of lines, thus having the same probability of errors. So, I guess - correct if I am wrong - there is no benefits of one over another when it comes to configuration errors. There is not a more concise programmability of a dynamic etherchannel that would be consider less prone to errors, when configuring etherchannels.  

[Joseph W. Doherty]

"So, I guess - correct if I am wrong - there is no benefits of one over another when it comes to configuration errors. There is not a more concise programmability of a dynamic etherchannel that would be consider less prone to errors, when configuring etherchannels."

You're missing a critical configuration consideration, configuration errors detectable on the device being configured and those using information between multiple devices.

For example, I try to configure a device with a, so far, unknown VLAN.  Device can immediately throw an error or do something like create the VLAN, with a message it did.

However if the far side port is configured with a differently configured VLAN, only some protocol sharing info between devices can flag the ports being configured in different VLANs.

[GabrielART · Accepted solution]

Great stuff Joseph, and thank you for the explanation. You are correct when it comes to all the other benefits when choosing a dynamic protocol over static. The constant negotiation and failover gives a peace of mind to the engineer, however, I still find cumbersome to have to go to both devices and setup groups, match the physical interfaces on both ends, tell port-channel that is a trunk if layer 2 etherchannel, etc. Even the modes are kind off, if you would think that if you set the device to active or desirable, the other end would automatically negotiate the rest without having to go to the other device and configure same settings. It is kind irrelevant these modes, desirable-desirable, desirable-auto, active-active, and active-passive when you have to configure both sides same. I am failing to see the dynamic part of the configuration itself, when you have to do it all manually in order to work dynamically. The appropriate word in my option would be "statefull", as it would keep the state or "track" of the links, and if one, or more goes down, it would failover. 

Thank you, and Flavio very much for taking the time to answer these trivial questions. This is a great community of very knowledgeable IT professionals and enthusiasts. It helps a lot. 

[M02@rt37 · Accepted solution]

Hello @GabrielART 

You raise an interesting and valid point about the perceived "dynamic" nature of etherhannel protocols like and PAgP. While these protocols are designed to provide redundancy, load balancing, and ease of link failover, the configuration process often feels more "manual" than truly "dynamic."

The main reason for this is that both sides of the link must share the same configuration parameters (e.g., port-channel group, mode, and Layer 2/Layer 3 settings) for the protocol to function properly. This symmetry ensures compatibility and prevents misconfigurations, but it does indeed require the network engineer to carefully configure both ends to match. Modes like active-passive in LACP or desirable-auto in PAgP add an extra layer of flexibility by negotiating the formation of the EtherChannel, but as you pointed out, the overall configuration still requires manual intervention on both devices.

Your observation that "stateful" might be a better descriptor than "dynamic" is insightful. These protocols are more about maintaining the operational state of the aggregated links—ensuring that they remain functional, balanced, and failover-ready—than about reducing configuration effort. The dynamic element lies in the automatic negotiation and adjustment of active links within the EtherChannel, not necessarily in the ease of initial setup.

In essence, while the protocols handle operational tasks dynamically, the setup remains a deliberate, manual process to ensure precision and avoid misalignment. Automation tools like ansible, python scripts, or controller-based solutions such as cisco DNAC can help reduce this manual burden, but the fundamental requirement for matching configurations on both ends of the link persists...

[GabrielART]

Beautifully explained M02@rt37. For us IT professionals trying to learn the network pillar of IT's many pillars, will be easier to understand and digest the etherchannel content from your explanation. Thank you for explaining. We learn a lot from more seasoned professionals. 

[Joseph W. Doherty]

In theory, and practice too, dynamic link bonding helps support sanity checks and preclude misconfigurations.  This usually comes at the expense of additional resource need supporting the protocol.

Conceptionally, somewhat similar considerations when comparing why use Ethernet auto negotiation, auto MDI/MDI-X, dynamic routing, CDP VLAN checking, etc.

As a side note, early versions of Etherchannel required similar port configurations, that later versions allowed more and more physical port configuration statements to be done on the port-channel interface.  I don't recall if this actually reduced the number of configuration statements, or possibly actually increased them, but it made configuration easier and less error prone.

So, if above unclear, the value of some dynamic approaches which only consider number of configuration statements is of little to almost zero value, compared to other considerations.