300-115 question 42 discussion


An access switch has been configured with an EtherChannel port. After configuring SPAN
to monitor this port, the network administrator notices that not all traffic is being replicated
to the management server. What is a cause for this issue?

  • A. VLAN filters are required to ensure traffic mirrors effectively.
  • B. SPAN encapsulation replication must be enabled to capture EtherChannel destination traffic.
  • C. The port channel can be used as a SPAN source, but not a destination.
  • D. RSPAN must be used to capture EtherChannel bidirectional traffic.
Created 11 months ago by behruzhuseyn


Answer B. Question says: "...After configuring SPAN to monitor this port," It means that SPAN source is etherchannel, not destination. Second fact, Question says : "...not all traffic..." this means that some traffic is mirrored. If you will use ehterchannel as the destination of SPAN session then you will not see anything at all on the management server. Answer is definitely B. You must use something like this: monitor session 1 destination interface F0/1 encapsulation replicate


A. VLAN filters are required to ensure traffic mirrors effectively.


Question is "What is a cause for this issue?" - not how to fix it. "encapsulation replication" won't help you, it is used to tag VLANs (when replicating trunk) Although I think this is not very good question, answer is C.


C A destination port cannot be an EtherChannel group. A destination port can be a physical port that is assigned to an EtherChannel group, even if the EtherChannel group has been specified as a SPAN source. The port is removed from the group while it is configured as a SPAN destination port.




The default configuration for local SPAN session ports is to send all packets untagged. SPAN also does not normally monitor bridge protocol data unit (BPDU) packets and Layer 2 protocols, such as Cisco Discovery Protocol (CDP), VLAN Trunk Protocol (VTP), Dynamic Trunking Protocol (DTP), Spanning Tree Protocol (STP), and Port Aggregation Protocol (PAgP). However, when you enter the encapsulation replicate keywords when configuring a destination port, these changes occur: (NB: "not all traffic is being monitored" seems to refer to BPDUs, CDP, VTP, STP, and PaGP control frames) •Packets are sent on the destination port with the same encapsulation—untagged, Inter-Switch Link (ISL), or IEEE 802.1Q—that they had on the source port. •Packets of all types, including BPDU and Layer 2 protocol packets, are monitored. Answer: B


THE ANSWER IS C Reference: https://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-series-switches/10570-41.html#anc63 Can You Configure SPAN on an EtherChannel Port? An EtherChannel does not form if one of the ports in the bundle is a SPAN destination port. If you try to configure SPAN in this situation, the switch tells you: Channel port cannot be a Monitor Destination Port Failed to configure span feature You can use a port in an EtherChannel bundle as a SPAN source port.