Cisco CCNA EtherChannel and Link Aggregation 2 — Questions and Answers
Question 1: Which command on a Cisco switch assigns a physical interface to EtherChannel group 1 using LACP active mode?
- channel-group 1 mode active (Correct answer)
- lacp group 1 active
- etherchannel 1 lacp active
- port-channel 1 active
Correct answer: channel-group 1 mode active
The 'channel-group 1 mode active' interface command assigns the port to port-channel 1 and enables LACP active negotiation.
Question 2: For an EtherChannel to form successfully, which of the following must match on all member ports?
- Port speed and duplex, native VLAN, and allowed VLANs (Correct answer)
- MAC addresses and interface descriptions
- IP addresses and subnet masks
- CDP timer values and hold-time settings
Correct answer: Port speed and duplex, native VLAN, and allowed VLANs
All EtherChannel member ports must have identical speed, duplex, native VLAN, and allowed VLAN lists or the bundle will not form.
Question 3: Which command verifies the status of all EtherChannel bundles on a Cisco switch?
- show interfaces trunk
- show etherchannel summary (Correct answer)
- show lacp neighbor
- show port-channel detail
Correct answer: show etherchannel summary
'show etherchannel summary' displays the port-channel group number, protocol, ports, and bundle state (SU = Layer 2 in use) in a compact format.
Question 4: What does the flag 'D' indicate for a port in the output of 'show etherchannel summary'?
- The port is the designated root port
- The port is in LACP active mode
- The port is down and not part of the active bundle (Correct answer)
- The port is a dynamic trunk port
Correct answer: The port is down and not part of the active bundle
The 'D' flag in 'show etherchannel summary' indicates the port is down, meaning it is not contributing to the active EtherChannel bundle.
Question 5: How does Spanning Tree Protocol (STP) treat an EtherChannel bundle?
- STP runs separately on each physical link in the bundle
- STP treats the entire EtherChannel as a single logical link (Correct answer)
- STP is disabled automatically when EtherChannel is configured
- STP blocks all but one physical link in the bundle
Correct answer: STP treats the entire EtherChannel as a single logical link
STP sees the entire EtherChannel port-channel as a single logical interface, so it does not block individual member links, allowing all bundled links to carry traffic.
Question 6: What happens when you configure one side of a link with EtherChannel mode 'On' and the other side with mode 'Active' (LACP)?
- The EtherChannel forms successfully using LACP
- The EtherChannel forms using PAgP as a fallback
- The EtherChannel fails to form because 'On' mode does not send or respond to negotiation packets (Correct answer)
- The switch automatically detects the mismatch and switches to passive mode
Correct answer: The EtherChannel fails to form because 'On' mode does not send or respond to negotiation packets
'On' mode forces EtherChannel without any negotiation protocol; it will not respond to LACP or PAgP packets, so the channel will not form with a negotiating peer.
Question 7: A Layer 3 EtherChannel differs from a Layer 2 EtherChannel in that it:
- Uses PAgP instead of LACP for negotiation
- Supports only two physical links instead of eight
- Has an IP address assigned directly to the port-channel interface (Correct answer)
- Requires VTP to be disabled before configuration
Correct answer: Has an IP address assigned directly to the port-channel interface
A Layer 3 EtherChannel is created with 'no switchport' on member interfaces; the port-channel interface itself receives an IP address and acts as a routed interface.
Cisco CCNA EtherChannel and Link Aggregation 2
Which command on a Cisco switch assigns a physical interface to EtherChannel group 1 using LACP active mode?