Cisco CCNA EtherChannel and Link Aggregation 1 — Questions and Answers
Question 1: What is the primary purpose of EtherChannel on a Cisco switch?
- To encrypt traffic between switches
- To bundle multiple physical links into a single logical link for increased bandwidth and redundancy (Correct answer)
- To separate broadcast domains across trunk links
- To provide dynamic IP address assignment to connected devices
Correct answer: To bundle multiple physical links into a single logical link for increased bandwidth and redundancy
EtherChannel aggregates multiple physical Ethernet links into one logical link, multiplying bandwidth and providing redundancy without Spanning Tree blocking ports.
Question 2: Which Cisco-proprietary protocol is used to negotiate EtherChannel formation between switches?
- LACP
- LLDP
- PAgP (Correct answer)
- CDP
Correct answer: PAgP
Port Aggregation Protocol (PAgP) is Cisco's proprietary protocol for automatically negotiating EtherChannel bundles between Cisco devices.
Question 3: Which IEEE standard defines the Link Aggregation Control Protocol (LACP)?
- IEEE 802.1Q
- IEEE 802.3ad (802.1AX) (Correct answer)
- IEEE 802.1D
- IEEE 802.11ac
Correct answer: IEEE 802.3ad (802.1AX)
LACP is defined in IEEE 802.3ad, later incorporated into IEEE 802.1AX, and is the vendor-neutral standard for link aggregation.
Question 4: What is the maximum number of physical links that can be bundled in a single EtherChannel on a Cisco switch?
- 4
- 6
- 8 (Correct answer)
- 16
Correct answer: 8
A Cisco EtherChannel supports up to 8 active physical links bundled into a single logical port-channel interface.
Question 5: Which PAgP mode causes a port to actively send PAgP packets to initiate an EtherChannel?
- Passive
- Auto
- Desirable (Correct answer)
- On
Correct answer: Desirable
PAgP 'desirable' mode actively initiates EtherChannel negotiation by sending PAgP packets, similar to LACP 'active' mode.
Question 6: Which LACP mode will form an EtherChannel only if the remote side also sends LACP packets?
- Active
- Passive (Correct answer)
- On
- Auto
Correct answer: Passive
LACP 'passive' mode will only respond to LACP packets; it does not initiate negotiation, so the remote side must be in 'active' mode.
Question 7: What load-balancing method does Cisco use by default for EtherChannel traffic distribution?
- Round-robin per packet
- Source MAC address (Correct answer)
- Destination IP address
- Least-loaded link
Correct answer: Source MAC address
Cisco's default EtherChannel load-balancing method is based on source MAC address, though this can be changed with the 'port-channel load-balance' command.
Cisco CCNA EtherChannel and Link Aggregation 1
What is the primary purpose of EtherChannel on a Cisco switch?