mediumMultiple ChoiceObjective-mapped
300-410 Practice Question: Runs the following command to troubleshoot an…
A network engineer runs the following command to troubleshoot an IPv4 Access Control Lists issue:
R1# debug ip packet 100 detail IP packet debugging is on for access list 100 *Mar 1 00:12:34.567: IP: s=10.1.1.1 (GigabitEthernet0/0), d=10.2.2.2, len 100, proto UDP, flags 0x0, sport 12345, dport 80, access list 100: matched line 10 permit udp host 10.1.1.1 host 10.2.2.2 eq 80 *Mar 1 00:12:35.123: IP: s=10.1.1.1 (GigabitEthernet0/0), d=10.2.2.2, len 100, proto TCP, flags 0x2, sport 12346, dport 443, access list 100: matched line 20 deny tcp host 10.1.1.1 host 10.2.2.2 eq 443 *Mar 1 00:12:35.124: IP: s=10.1.1.1 (GigabitEthernet0/0), d=10.2.2.2, len 100, proto TCP, flags 0x10, sport 12346, dport 443, access list 100: matched line 20 deny tcp host 10.1.1.1 host 10.2.2.2 eq 443
What does this output indicate?
⚠ Common exam trap
Cisco often tests the ability to distinguish inbound vs. outbound ACL application by interpreting the source and destination IP addresses in debug output, where the trap is that candidates mistakenly assume the ACL is outbound because the destination IP is different, ignoring that the source interface reveals the direction.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The ACL is applied inbound on GigabitEthernet0/0 and is permitting UDP traffic to port 80 while denying TCP traffic to port 443.
The debug output shows packets entering GigabitEthernet0/0 (source interface) and matching ACL 100. The first packet (UDP to port 80) matches line 10 (permit), while subsequent TCP packets to port 443 match line 20 (deny). Since the source interface is the inbound interface, the ACL is applied inbound. This confirms Option A: the ACL permits UDP to port 80 and denies TCP to port 443.
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 ACL is applied inbound on GigabitEthernet0/0 and is permitting UDP traffic to port 80 while denying TCP traffic to port 443.
Why this is correct
The debug output shows that UDP traffic to port 80 matches line 10 (permit) and TCP traffic to port 443 matches line 20 (deny).
- ✗
The ACL is applied outbound on GigabitEthernet0/0 and is permitting all traffic.
Why it's wrong here
The debug shows deny matches, not just permit.
- ✗
The ACL is misconfigured because TCP traffic to port 443 should be permitted.
Why it's wrong here
The ACL is correctly denying TCP to port 443 as per the debug.
- ✗
The ACL is not applied to any interface because debug ip packet shows only the ACL number.
Why it's wrong here
The debug shows the interface (GigabitEthernet0/0) and the ACL matches.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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