Select the three PAgP channel establishment modes. (Choose three.)

The three PAgP channel establishment modes are auto, desirable, and on. Auto waits for PAgP signals, desirable actively negotiates, and on forces the channel without negotiation. Understanding these modes helps in configuring EtherChannel effectively. For more networking tips, visit Study4Pass.

Tech Professionals

08 April 2025

Cisco

Select the three PAgP channel establishment modes. (Choose three.)

Introduction

Port Aggregation Protocol (PAgP) is a Cisco proprietary protocol used to automate the creation of EtherChannel links between switches. It ensures efficient bandwidth utilization and redundancy in network setups. When configuring EtherChannel, selecting the appropriate PAgP mode is crucial for establishing a stable and high-performance network.

This article explores the three primary PAgP channel establishment modes, their functionalities, and their relevance in CCNP Enterprise (350-401 ENCOR) and CCIE Enterprise Wireless exams. Additionally, we recommend Study4Pass as an excellent resource for mastering these concepts through structured study materials and practice exams.

What is PAgP?

PAgP (Port Aggregation Protocol) facilitates the automatic bundling of multiple physical Ethernet links into a single logical link (EtherChannel). It enhances bandwidth, provides redundancy, and simplifies network management.

PAgP operates by exchanging packets between switches to negotiate the formation of an EtherChannel. The three key PAgP modes are:

Auto
Desirable
On (Manual)

Each mode determines how aggressively a switch attempts to form an EtherChannel.

Auto Mode

Definition

Auto mode is a passive PAgP mode where the switch listens for PAgP packets from the neighboring switch but does not initiate the negotiation.

Behavior

The switch waits for the other end to send PAgP requests.
If the neighboring switch is in Desirable mode, an EtherChannel is formed.
If the neighboring switch is also in Auto, no EtherChannel is established (both are passive).

Use Case

Useful when you want a switch to form an EtherChannel only if the other switch actively requests it.
Prevents accidental channel formation in misconfigured networks.

Configuration Example

Switch(config)# interface range GigabitEthernet0/1 - 2

Switch(config-if-range)# channel-protocol pagp

Switch(config-if-range)# channel-group 1 mode auto

Desirable Mode

Definition

Desirable mode actively attempts to negotiate an EtherChannel by sending PAgP packets to the neighboring switch.

Behavior

The switch initiates PAgP negotiations.
Forms an EtherChannel if the other switch is in Auto or Desirable mode.
Does not form an EtherChannel if the other side is in On (Manual) mode (since PAgP is disabled in manual mode).

Use Case

Preferred in environments where dynamic EtherChannel formation is needed.
Ensures faster link aggregation compared to Auto mode.

Configuration Example

Switch(config)# interface range GigabitEthernet0/1 - 2

Switch(config-if-range)# channel-protocol pagp

Switch(config-if-range)# channel-group 1 mode desirable

On Mode (Manual EtherChannel)

Definition

On mode forces the interface into an EtherChannel without PAgP or LACP negotiation.

Behavior

No PAgP packets are exchanged.
EtherChannel is formed only if the other switch is also in On mode.
Misconfiguration can lead to switching loops (if one side is PAgP and the other is LACP).

Use Case

Used when connecting to non-Cisco devices that do not support PAgP.
Requires manual verification to avoid errors.

Configuration Example

Switch(config)# interface range GigabitEthernet0/1 - 2

Switch(config-if-range)# channel-group 1 mode on

Comparison of PAgP Modes

Mode	Sends PAgP Packets?	Forms EtherChannel With	Recommended Use
Auto	No (Passive)	Desirable	Passive negotiation
Desirable	Yes (Active)	Auto, Desirable	Active negotiation
On	No (Forced)	On (Manual)	Non-PAgP devices

Best Practices for PAgP Configuration

Use Desirable-Desirable or Desirable-Auto for dynamic EtherChannel setups.
Avoid Auto-Auto as it will not form an EtherChannel.
Ensure Consistency—both ends must use compatible modes.
Verify with show etherchannel summary to confirm EtherChannel status.

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Comprehensive Study Guides – Detailed explanations of PAgP, EtherChannel, and other key topics.
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Expert Support – Access to certified professionals for doubt resolution.

By leveraging Study4Pass, candidates can gain confidence in configuring PAgP modes and other advanced networking concepts, ensuring exam success.

Conclusion

Understanding PAgP channel establishment modes (Auto, Desirable, On) is essential for network engineers pursuing CCNP Enterprise and CCIE certifications. Proper configuration ensures optimal bandwidth utilization and network redundancy.

For structured learning and exam success, Study4Pass provides the best resources, including study guides, practice exams, and expert guidance. Start your journey toward Cisco certification mastery today!

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Note: This article is part of the CCNP Enterprise (350-401 ENCOR) and CCIE Enterprise Wireless study series. For more in-depth tutorials, visit Study4Pass.