Which Statement Is True Regarding the Use of PAgP to Create EtherChannels? Explained

EtherChannel is a robust method used in network engineering to combine multiple physical links into one logical link for increased bandwidth and redundancy. One key protocol that helps create EtherChannels is PAgP (Port Aggregation Protocol), developed by Cisco. Understanding the role of PAgP is crucial for anyone pursuing certifications like CCNA or preparing through platforms like DumpsQueen.

In this comprehensive guide, we will answer the frequently asked question: “Which statement is true regarding the use of PAgP to create EtherChannels?” We’ll explore how PAgP works, its configurations, advantages, and provide multiple-choice questions to test your knowledge.

What Is EtherChannel?

EtherChannel allows for the bundling of up to eight physical Ethernet links to create a single logical link, increasing throughput and providing fault tolerance. EtherChannels are commonly used between switches, routers, and servers in enterprise environments.

What Is PAgP?

PAgP, or Port Aggregation Protocol, is a Cisco-proprietary protocol used to automate the creation of EtherChannels. It negotiates with the remote device to ensure compatibility before forming a channel.

Why Understanding PAgP Is Important

Whether you're preparing for Cisco certifications or deploying real-world networks, understanding how PAgP works can save time and prevent misconfiguration. Since it's vendor-specific, knowing the distinctions between PAgP and other protocols like LACP (Link Aggregation Control Protocol) is essential.

Which Statement Is True Regarding the Use of PAgP to Create EtherChannels?

Let’s break down this question in a structured way. You may find multiple options in exams, but only one of them accurately describes how PAgP functions. Here's the correct statement:

True Statement: PAgP can automatically configure EtherChannel between Cisco devices when interfaces are set to desirable or auto mode.

This statement is true because PAgP has two modes: desirable and auto. When one end is set to "desirable" and the other to "auto," or both ends are set to "desirable," the EtherChannel will form.

PAgP Modes Explained

For example:

• If Switch A is set to auto and Switch B is set to auto, no EtherChannel forms.
• If Switch A is desirable and Switch B is auto, the EtherChannel will form.
• If both are desirable, EtherChannel forms successfully.

PAgP Configuration Example

bash

SwitchA(config)# interface range fa0/1 - 2

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

SwitchA(config-if-range)# exit

SwitchA(config)# interface port-channel 1

SwitchA(config-if)# switchport mode access

Repeat similar configuration on the other switch but use mode auto or desirable.

PAgP vs LACP

Understanding the difference between PAgP and LACP is important when dealing with multi-vendor environments.

PAgP Benefits

• Automatic Configuration: Reduces human error during setup.
• Load Balancing: Distributes traffic across links.
• Redundancy: If one link fails, others continue to work.
• Prevention of Switching Loops: STP sees the EtherChannel as one logical link.

Limitations of PAgP

• Works only on Cisco devices.
• Limited flexibility in mixed vendor environments.
• Incompatibility with LACP configurations.

When to Use PAgP

• In Cisco-only environments.
• When administrators want to leverage Cisco’s proprietary automation.
• In training labs or certification preparation scenarios where Cisco hardware is used.

When Not to Use PAgP

• In mixed vendor environments—use LACP instead.
• When you require support for standards-based protocols.

Troubleshooting PAgP EtherChannels

Sometimes PAgP EtherChannels may not form as expected. Here are a few steps to troubleshoot:

1. Check Interface Modes: Ensure one end is "desirable" and the other is "auto" or "desirable".
2. Consistent Configuration: Speed, duplex, and VLAN settings must match on all member interfaces.
3. Verify with show pagp Command:

bash

Switch# show pagp neighbor

4. Check for Errors: Use show etherchannel summary and show interfaces for diagnostics.

Best Practices

• Avoid configuring EtherChannels across different modules in chassis switches unless supported.
• Ensure all links in a channel group have the same speed and duplex.
• Avoid mixing PAgP with LACP configurations.

Real-World Use Case

In a Cisco-only data center environment, multiple switches are linked using EtherChannel to increase uplink capacity. Network engineers use PAgP for quick configuration and to avoid manual synchronization of interfaces. PAgP ensures that links aggregate correctly without misconfigurations, thereby preventing STP reconvergence delays.

Conclusion

Understanding PAgP and its application in EtherChannel formation is a foundational skill for network professionals. To confidently answer the question “Which statement is true regarding the use of PAgP to create EtherChannels?” you need to know the modes, configurations, and behaviors of the protocol. Whether you're preparing for a certification or configuring enterprise switches, PAgP remains a valuable tool in your networking toolkit.

DumpsQueen provides reliable, up-to-date preparation materials and insights to help candidates not just pass exams but also understand real-world networking concepts. Master protocols like PAgP through detailed guides, practice questions, and real exam scenarios.

Sample MCQs: PAgP and EtherChannel

Question 1:
Which mode combination will allow PAgP to successfully form an EtherChannel?

A. Auto / Auto
B. Desirable / Auto
C. Passive / Passive
D. Active / Passive

Correct Answer: B. Desirable / Auto

Question 2:
Which statement is true regarding the use of PAgP to create EtherChannels?

A. PAgP is an open standard supported by all vendors
B. PAgP allows EtherChannels to be formed only in auto mode
C. PAgP negotiates automatic EtherChannel creation between Cisco devices
D. PAgP is only used for Layer 3 EtherChannels

Correct Answer: C. PAgP negotiates automatic EtherChannel creation between Cisco devices

Question 3:
What is the result if both ends of a link are set to PAgP auto mode?

A. EtherChannel forms successfully
B. EtherChannel forms only if VLANs match
C. No EtherChannel is formed
D. The ports go into err-disabled state

Correct Answer: C. No EtherChannel is formed

Question 4:
PAgP is best suited for which type of environment?

A. Multi-vendor networks
B. Cisco-only environments
C. IPv6-only environments
D. Cloud-native deployments

Correct Answer: B. Cisco-only environments

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