If we are talking of a LAG in this chapter, we talk about link aggregation group. It is used between ports connecting the same switches.
If you have a LAG with 2x 1Gbit/s connection, there won’t be a possibility that one single connection uses more than 1 Gbit/s. But you have the chance that 2 connections each use 1 Gbit/s so you increase the bandwidth of the total throughput but not the bandwidth of one single connection. If you want true fragmentation and increase the bandwidth for one connection you have to use something called MLPPP.
You can use LAGs as well for AccessPoints, so you have redundancy and more total bandwidth for all the connected devices.
3 ways for EtherChannel to work:
- Static
static means you manually configure the EtherChannel Ports for each switch to be a EtherChannel port. But static has inherit danger, if one site is misconfigured you could cause loops because it does not block loops for example. - PAGP
Cisco protocol, you have to have all Cisco switches everywhere, but you want to use LAGs as well to WAPs or servers and all of that has to be Cisco. - LACP
Allow you to negotiate those connections (EtherChannel). Like you send little hello packets “hey I want to do EtherChannel”, if one site is misconfigured it tears down the EtherChannel and run normal STP and make sure the link gets blocked and you don’t have a loop in your network.
Configuring EtherChannels with LACP
| command | Mode | description |
| channel-group 1 mode | On | This is static -> don’t use it in the real world! |
| Auto | This is for PAGP, if both ports are set to auto nothing happens, there has to be one aggressive to form a relationship | |
| Desirable | This is for PAGP, this is the aggressive mode, you can just put both ends in this mode, and the relationship is formed | |
| Passive | This is for LACP, if you have two passive ports, they won’t form a relationship, it’s like the auto state for PAGP | |
| Active | This is for LACP, if you have two active ports, they form a relationship or if you have one passive and one active port they will form a relationship as well |
When you form an EtherChannel, there will be a new interface created, PortChannel1 is the virtual interface to represent the EtherChannel connection. There is where you put your config for the EtherChannel.
Tuning EtherChannel Load Balancing
Command to identify: show etherchannel load-balance
Operational state -> src-mac -> that means that the different source mac addresses chooses the different links
Maybe your scenario is different, when you only have one server, this server only uses this one line to communicate back, and that could be inefficient. We have to change that setting on both switches.
Change command: port-channel load-balance <dst-ip OR dst-mac OR src-dst-ip>
It puts the combination of A and B in a blender, and gets a hash, this hash decides which line the data go.
Deploying EtherChannel at Castle Rysen Coffee
Checklist for deployment of EtherChannel
- Verify identical port configuration
- Configure LACP communication
- Verify VLAN configuration
- Verify Etherchannel active
- (optional) modify load balancing Algorithm
Cisco IOS commands learned in this chapter
| Command | Description | ||||
| Interface | Range | Gigabitethernet0/1 | – | 2 | Enters interface configuration mode for multiple ports simultaneously |
| Channel-group | <NUMBER> | Mode | active | LACP aggressive mode (initiates negotiation) | |
| Passive | LACP waiting mode (only responds if the other side is active) | ||||
| Desirable | PAgP aggressive mode (Cisco proprietary) | ||||
| auto | PAgP waiting mode (Cisco proprietary) | ||||
| On | Force static bundling (no negotiation protocol, creates loop risks) | ||||
| Interface | Port-channel | <NUMBER> | Enters configuration mode for the newly created virtual representation of the bundle | ||
| Port-channel | Load-balance | Src-mac | Changes the hashing algorithm to Source MAC address | ||
| Dst-mac | Changes the hashing algorithm to Destination MAC address | ||||
| Dst-ip | Changes the hashing algorithm to Destination IP address | ||||
| Src-dst-ip | Blends source and destination IP addresses into a hash | ||||
| Show | Etherchannel | Load-balance | Displays the current operational load-balancing hash mechanism configured on the switch | ||
| Show | Etherchannel | Summary | Provides a summary of the EtherChannel groups configured on the switch, showing which protocol is active and which physical ports are successfully bundled |