EtherChannel Configuration Using LACP, PAgP and Static
Objectives
- Configure EtherChannel using LACP, PAgP and Static modes.
- Understand the differences between LACP, PAgP and Static EtherChannel.
- Verify EtherChannel formation using Cisco IOS commands.
- Understand how EtherChannel provides increased bandwidth, redundancy and load balancing.
Theory
EtherChannel is a Cisco technology that allows multiple physical Ethernet links to be bundled together into one logical link. This increases available bandwidth and provides redundancy between network devices. If one physical link fails, traffic can continue through the remaining active links.
There are three main methods of configuring EtherChannel: LACP, PAgP and Static. Each method has different negotiation mechanisms and configuration modes.
1. LACP (Link Aggregation Control Protocol)
LACP is an open-standard protocol defined by IEEE 802.3ad, now incorporated into IEEE 802.1AX. It allows devices from different vendors to negotiate and establish an EtherChannel.
| Mode | Description |
|---|---|
| Active | Actively sends LACP packets to negotiate an EtherChannel. |
| Passive | Waits for the other device to initiate LACP negotiation. |
An EtherChannel using LACP can form when one side is Active and the other side is Active or Passive. Two Passive interfaces will not form a channel.
2. PAgP (Port Aggregation Protocol)
PAgP is a Cisco-proprietary protocol used to automatically negotiate EtherChannel formation between compatible Cisco devices.
| Mode | Description |
|---|---|
| Desirable | Actively sends PAgP packets to negotiate an EtherChannel. |
| Auto | Waits for the other device to initiate PAgP negotiation. |
PAgP forms an EtherChannel when at least one side is configured as Desirable. Two Auto interfaces will not form a channel.
3. Static EtherChannel
Static EtherChannel is manually configured without using a negotiation protocol. Both ends must be configured with the same channel settings.
| Configuration | Description |
|---|---|
| Mode on | Manually forces the physical interfaces to join an EtherChannel without negotiation. |
Comparison of EtherChannel Protocols
| Feature | LACP | PAgP | Static |
|---|---|---|---|
| Standard | IEEE 802.3ad / 802.1AX | Cisco proprietary | No negotiation protocol |
| Modes | Active / Passive | Desirable / Auto | On |
| Negotiation | Yes | Yes | No |
| Vendor support | Multi-vendor | Cisco devices | Compatible devices with matching static configuration |
How EtherChannel Load Balancing Works
EtherChannel distributes traffic across its active member links using a hashing algorithm. The algorithm can use information such as source and destination MAC addresses, IP addresses or TCP/UDP port numbers, depending on the switch configuration.
Traffic is not normally distributed packet by packet across all links. Instead, traffic flows are assigned to member links based on the hashing calculation. This helps maintain packet order while sharing traffic across the available links.
Network Topology
Interface and EtherChannel Mode
| Sl. No | Switches | Ports | Port Channel | EtherChannel Type |
|---|---|---|---|---|
| 1 | Switch0 and Switch1 | Fa0/1 - Fa0/2 | Po1 | LACP |
| Fa0/3 - Fa0/4 | Po2 | Static | ||
| Fa0/5 - Fa0/6 | Po3 | PAgP | ||
| 2 | Switch2 and Switch3 | Fa0/1 - Fa0/2 | Po1 | LACP |
| Fa0/5 - Fa0/6 | Po3 | PAgP |
Configuration Commands
1. Switch0 and Switch1 Configuration
Switch0 and Switch1
enable configure terminal ! LACP EtherChannel - Port Channel 1 interface range fa0/1-2 switchport mode trunk channel-group 1 mode active exit interface port-channel 1 switchport mode trunk no shutdown exit ! Static EtherChannel - Port Channel 2 interface range fa0/3-4 switchport mode trunk channel-group 2 mode on exit interface port-channel 2 switchport mode trunk no shutdown exit ! PAgP EtherChannel - Port Channel 3 interface range fa0/5-6 switchport mode trunk channel-group 3 mode desirable exit interface port-channel 3 switchport mode trunk no shutdown exit end write memory
2. Switch2 and Switch3 Configuration
Switch2 and Switch3
enable configure terminal ! LACP EtherChannel - Port Channel 1 interface range fa0/1-2 switchport mode trunk channel-group 1 mode active exit interface port-channel 1 switchport mode trunk no shutdown exit ! PAgP EtherChannel - Port Channel 3 interface range fa0/5-6 switchport mode trunk channel-group 3 mode desirable exit interface port-channel 3 switchport mode trunk no shutdown exit end write memory
Important: Apply the Switch0 and Switch1 configuration separately on both switches. Likewise, apply the Switch2 and Switch3 configuration separately on both switches. The connected switches must have matching channel-group numbers, compatible protocols and compatible interface settings.
Verification Commands & Outputs
After configuring EtherChannel on both ends, use the following commands to check whether the port channels have formed successfully.
1. Verify EtherChannel Summary
Flags: D - down P - bundled in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator
Group Port-channel Protocol Ports
------+-------------+-----------+-------------------------
1 Po1(SU) LACP Fa0/1(P) Fa0/2(P)
2 Po2(SU) - Fa0/3(P) Fa0/4(P)
3 Po3(SU) PAgP Fa0/5(P) Fa0/6(P)
Explanation: The SU status indicates that the Layer 2 port channel is in use. The P flag beside each interface indicates that the physical interface is successfully bundled into the EtherChannel.
2. Verify EtherChannel Details
Group state = L2 Ports: 2 Maxports = 8 Port-channels: 1 Max Port-channels = 16 Port state = Port-channel Ag-Inuse Protocol = LACP Ports in the group: ------------------- Port: Fa0/1 Port state = Up Mstr In-Bndl Port: Fa0/2 Port state = Up Mstr In-Bndl
This command displays detailed information about the EtherChannel groups, member interfaces and negotiation protocols. The exact output depends on the switch model and IOS version.
3. Verify LACP Counters
Port LACP PDU Marker PDU
Sent Recv Sent Recv
Fa0/1 100 100 0 0
Fa0/2 100 100 0 0
4. Verify PAgP Counters
Port PAgP PDU Marker PDU
Sent Recv Sent Recv
Fa0/5 100 100 0 0
Fa0/6 100 100 0 0
5. Verify LACP Neighbors
Flags: S - Device is requesting Slow LACPDUs
F - Device is requesting Fast LACPDUs
A - Active P - Passive
Channel group 1 neighbors
Partner's information:
Partner Partner
Port Flags System ID Port Number
Fa0/1 SA xxxx.xxxx.xxxx 1
Fa0/2 SA xxxx.xxxx.xxxx 2
Note: The outputs above are illustrative examples. Actual counters, system IDs, flags and port states will differ depending on the switch model, configuration and lab environment. Some Packet Tracer switch models may not support every detailed verification command.
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