The answer is that a routing problem is causing packets to be dropped in one direction. This conclusion is drawn directly from the IPsec SA packet counters asymmetry shown in the output, where 1,500 packets were encapsulated and sent outbound, but only 1,200 packets were decapsulated and received inbound. Such a mismatch between the encaps and decaps counters indicates that traffic is flowing successfully from the local router to the peer, but a portion of the return traffic is being lost, typically due to a missing or misconfigured route on the remote side. On the ENCOR 350-401 exam, this scenario tests your ability to interpret the show crypto ipsec sa command and recognize that asymmetric packet counters point to a unidirectional routing issue rather than an encryption or authentication failure. A common trap is to assume the problem is with the crypto map or ACL, but the counters clearly show encryption and decryption are working—only the volume differs. Memory tip: think of it like a two-way street—if more cars leave than arrive, there’s a roadblock on the return trip.
CCNP VPN Technologies Practice Question
This 350-401 practice question tests your understanding of vpn technologies. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A network engineer runs the following command on Router R2:
R2# show crypto ipsec sa peer 10.2.2.2
interface: Tunnel0
Crypto map tag: CMAP, local addr 10.1.1.2
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
There is a routing problem causing packets to be dropped in one direction.
The packet counters show 1500 packets encapsulated (sent) but only 1200 decapsulated (received). This asymmetry indicates possible packet loss or a routing issue in one direction.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The IPsec tunnel is functioning correctly with no issues.
Why it's wrong here
The mismatch in packet counts suggests a problem; a healthy tunnel would have roughly equal counts.
✓
There is a routing problem causing packets to be dropped in one direction.
Why this is correct
The difference between encaps and decaps counts indicates that some packets sent are not being received, likely due to routing or firewall issues.
The tunnel is using compression, as shown by the compress counters.
Why it's wrong here
The compress counters are zero, so no compression is being used.
✗
The remote peer is not responding to IKE requests.
Why it's wrong here
The presence of decapsulated packets shows the remote peer is responding; the issue is packet loss.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Trap categories for this question
Command / output trap
The presence of decapsulated packets shows the remote peer is responding; the issue is packet loss.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 350-401 subnetting questions on CIDR, address ranges, and subnet selection.
VPN Technologies — This question tests VPN Technologies — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: There is a routing problem causing packets to be dropped in one direction. — The packet counters show 1500 packets encapsulated (sent) but only 1200 decapsulated (received). This asymmetry indicates possible packet loss or a routing issue in one direction.
What should I do if I get this 350-401 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 350-401 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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