Port-Channels

A port channel, also known as a link aggregation group or channel group, is a technology that allows multiple physical interfaces to be grouped together into a single logical interface. 

This logical interface is used to increase the bandwidth, provide redundancy, and improve the reliability of the network. PortChannels are commonly used in enterprise networks to increase the capacity of the network and to provide redundancy in the event of a link failure. There are several types of PortChannels, including Static PortChannels, Port Aggregation Protocol (PaGP), and Link Aggregation Protocol (LACP). In this blog post, we will discuss each of these types in detail, including their configuration and verification.

Static PortChannel

Static PortChannel is the simplest form of PortChannel configuration. In this configuration, the administrator manually selects the interfaces to include in the channel and defines the channel number. All the physical links must have the same speed, duplex, and VLAN membership. Static PortChannels do not send any messages to negotiate with other devices.

The "Static" mode is a configuration in which the link aggregation is manually configured without using any protocol such as LACP or PAGP. It is similar to the "On" mode but requires manual configuration on both ends of the link, rather than relying on the ports to be always enabled for link aggregation. This mode is often used in situations where LACP or PAGP is not available or cannot be used

Configuration

To configure a static PortChannel, follow these steps:

1. Configure the physical interfaces as L2 or L3 access or trunk ports.
2. Create a PortChannel interface and assign a channel number.
3. Add the physical interfaces to the PortChannel interface.

Here is an example configuration for a static PortChannel using two physical interfaces (Ethernet 1/1 and Ethernet 1/2) and channel number 1:

Switch(config)# interface range Ethernet 1/1 - 2
Switch(config-if-range)# channel-group 1 mode on
Switch(config-if-range)# switchport mode trunk

Switch(config-if-range)# exit

Switch(config)# interface Port-Channel 1
Switch(config-if)# switchport mode trunk
Switch(config-if)# spanning-tree portfast trunk
Switch(config-if)# exit

Verification

Switch# show etherchannel summary

This command shows the PortChannel status, the number of physical interfaces in the PortChannel, and the operational state of each physical interface.

Link Aggregation Protocol (LACP)

Link Aggregation Control Protocol (LACP) is a standards-based protocol that also dynamically groups multiple physical links into a single logical link. LACP uses a negotiation process to determine if a potential PortChannel partner is capable of supporting LACP. If the partner is capable, LACP will attempt to form a PortChannel. If the partner is not capable, LACP will not form a PortChannel.

Configuration

To configure LACP, follow these steps:

1. Configure the physical interfaces as L2 or L3 access or trunk ports.
2. Enable LACP on the physical interfaces.
3. Create a PortChannel interface and assign a channel number.

Here is an example configuration for an LACP PortChannel using two physical interfaces (Ethernet 1/1 and Ethernet 1/2) and channel number 1:

Switch(config)# interface range Ethernet 1/1 - 2
Switch(config-if-range)# switchport mode trunk
Switch(config-if-range)# channel-group 1 mode active
Switch(config-if-range)# exit

Switch(config)# interface Port-Channel 1
Switch(config-if)# switchport mode trunk
Switch(config-if)# spanning-tree portfast trunk
Switch(config-if)# exit

Modes in LACP

In LACP, "Active" and "Passive" modes refer to the way that the LACP packets are sent and received during the negotiation process. In "Active" mode, the device sends LACP packets to actively negotiate link aggregation, while in "Passive" mode, the device waits for incoming LACP packets to initiate link aggregation negotiation.

Verification

Switch# show etherchannel summary

Port Aggregation Protocol (PaGP)

Port Aggregation Protocol (PaGP) is a Cisco proprietary protocol that dynamically groups multiple physical links into a single logical link. PaGP uses a negotiation process to determine if a potential PortChannel partner is capable of supporting PaGP. If the partner is capable, PaGP will attempt to form a PortChannel. If the partner is not capable, PaGP will fall back to a static PortChannel.

Configuration

To configure PaGP, follow these steps:

1. Configure the physical interfaces as L2 or L3 access or trunk ports.
2. Enable PaGP on the physical interfaces.
3. Create a PortChannel interface and assign a channel number.

Here is an example configuration for a PaGP PortChannel using two physical interfaces (Ethernet 1/1 and Ethernet 1/2) and channel number 1:

 

Switch(config)# interface range Ethernet 1/1 - 2
Switch(config-if-range)# switchport mode trunk
Switch(config-if-range)# channel-group 1 mode desirable
Switch(config-if-range)# exit

Switch(config)# interface Port-Channel 1
Switch(config-if)# switchport mode trunk
Switch(config-if)# spanning-tree portfast trunk
Switch(config-if)# exit

Modes in PaGP

In PAGP, "Desirable" and "Auto" modes are similar to LACP's "Active" and "Passive" modes, respectively. "On" mode is a static configuration that enables link aggregation without any negotiation, while still allowing the use of LACP or PAGP to detect and handle link failures.

Verification

Switch# show etherchannel summary

This command shows the PortChannel status, the number of physical interfaces in the PortChannel, and the operational state of each physical interface

Conclusion

PortChannels provide redundancy, high availability, and increased bandwidth to enterprise networks. Static PortChannels, PaGP, and LACP are three types of PortChannels that can be used in a network. Each PortChannel type has its own advantages and disadvantages, and the appropriate type should be chosen based on the network requirements.