Troubleshooting Layer 2 Switching

 In 200-301 V1 Ch08: Virtual LANs, 200-301 V1 Part 3: VLANs, STP, CCENT-OLD, Q&A

Layer 2 switching seems easy – but then you must think through how it works in a real network. Applying the ideas proves whether you really understood the concepts or not. This next question gives you that kind of practice again. As usual with the videos in this series, this post’s topics tie into at least one of the videos in recently-released CCENT Exam Prep LiveLessons video product. Specifically: How do VLANs and VLAN related config affect layer 2 switch forwarding? Today’s post is the question; next post is the answer.

The Question

In this network, all hosts use the IP address/mask configurations as shown. All links physically work and all switches act as layer 2 switches. Host 1 can successfully ping server A, but host 2’s ping of server A fails. Which answers list issue that could result these failure symptoms?

a) Host 2’s switch port is configured with a VLAN other than VLAN 2.

b) The SW3 to SW1 trunk is configured to disallow VLAN 2.

c) SW1 has shut down VLAN 2.

d) On the link between SW3 and SW1, both switches use a trunking negotiation mode of auto.

e) VLAN 2 has been removed from SW3’s configuration.


Figure 1: Diagram for the Switch Forwarding Question


More Background and Practice with CCENT EPL

As with all these recent questions published early in 2017, I picked the topic because of at least one of the videos in the new CCENT EPL product. For this one, some of the ideas behind this question are related to video 7.2, titled “Choosing the Correct VLAN for Frame Forwarding”. You can check out some other sample videos from the product at the CCENT EPL product web page.


Answer Post in a Few Days!

I’ll post an answer post in a few days. Watch for it! It should be the next post in chronological order as well, so watch for the link at the bottom of this page.

OSPFv2 Enabler #3 - Answers
Troubleshooting Layer 2 Switching: Answers
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Host 2 access port on Sw3 is configured to a VLAN other than 2


Thanks for playing, Xo!
Answer post is live in about an hour from now. We’ll see how I answered. 🙂


I think that A is the correct answer

Punya Athma

answer is: a. Answer b is excluded because host 1 can successfully ping server A, therefore VLAN 2 is allowed on the trunk between SW3 and SW1. Answer c is excluded because SW1 not shut down VLAN2 as host 1 can ping server A. Answer d excluded because the trunking mode between SW1 and SW3 operational as host 1 can ping server A. Answer e excluded because VLAN 2 not removed from SW3’s configuration as host 1 is in VLAN 2 and PC1 pings successfully to server A. So the conclusion is host 2’s switch port configured other than in VLAN 2.

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