Quick Answer
The correct answer is that traffic not from the 10.0.0.0/8 network is denied. This is because Cisco access control lists are processed in sequential order from top to bottom, and the first matching entry determines the action; here, entry 10 permits all traffic sourced from the 10.0.0.0/8 range, while entry 20 explicitly denies everything else, mirroring the implicit deny any any at the end. On the Cisco CCNP ENARSI 300-410 exam, interpreting show ip access-lists output with permit/deny order tests your ability to read the sequence numbers and match counts, ensuring you understand that a permit followed by a deny creates a selective allow policy. A common trap is assuming the explicit deny entry is unnecessary, but it confirms the behavior and can be used to track denied packets. Remember the memory tip: “First match wins—permit the good, deny the rest.”
This 300-410 practice question tests your understanding of ipv4 access control lists. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 R1:
R1# show ip access-lists
Extended IP access list 150
10 permit ip 10.0.0.0 0.255.255.255 any (500 matches)
20 deny ip any any (100 matches)Based on this output, which statement is correct?
Traffic from 10.0.0.0/8 is denied.
Why wrong: Line 10 permits it with 500 matches.
Traffic not from 10.0.0.0/8 is denied.
Line 20 denies all other traffic with 100 matches.
All traffic is permitted.
Why wrong: Line 20 denies traffic not matching line 10.
The ACL has no effect.
Why wrong: Match counts show it is active.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Traffic not from 10.0.0.0/8 is denied.
The ACL 150 has a permit entry for source 10.0.0.0/8 (wildcard 0.255.255.255) followed by a deny any any. Traffic matching the permit (from 10.0.0.0/8) is allowed, while all other traffic is denied by the implicit deny or the explicit deny entry. Thus, traffic not from the 10.0.0.0/8 network is denied, making option B correct.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Traffic from 10.0.0.0/8 is denied.
Why it's wrong here
Line 10 permits it with 500 matches.
Traffic not from 10.0.0.0/8 is denied.
Why this is correct
Line 20 denies all other traffic with 100 matches.
Related concept
Read the scenario before looking for a memorised answer.
All traffic is permitted.
Why it's wrong here
Line 20 denies traffic not matching line 10.
The ACL has no effect.
Why it's wrong here
Match counts show it is active.
Common exam traps
Cisco often tests the misconception that an ACL with a permit entry followed by a deny entry permits all traffic, when in fact the deny explicitly blocks everything not matching the earlier permit.
Trap categories for this question
Command / output trap
Match counts show it is active.
Detailed technical explanation
Cisco ACLs process entries in sequential order until a match is found; the first matching entry (permit or deny) is applied. The wildcard mask 0.255.255.255 in the permit entry matches the first octet exactly (10) and any value in the remaining three octets, effectively matching the 10.0.0.0/8 prefix. The explicit deny any any at the end ensures all non-matching traffic is dropped, and the 100 matches confirm this behavior in a real network scenario.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
IPv4 Access Control Lists — This question tests IPv4 Access Control Lists — Read the scenario before looking for a memorised answer..
The correct answer is: Traffic not from 10.0.0.0/8 is denied. — The ACL 150 has a permit entry for source 10.0.0.0/8 (wildcard 0.255.255.255) followed by a deny any any. Traffic matching the permit (from 10.0.0.0/8) is allowed, while all other traffic is denied by the implicit deny or the explicit deny entry. Thus, traffic not from the 10.0.0.0/8 network is denied, making option B correct.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A network engineer runs the following command on Router R1: R1# show ip access-lists Extended IP access list 180 10 permit tcp 192.168.1.0 0.0.0.255 any eq 80 (50 matches) 20 permit tcp 192.168.2.0 0.0.0.255 any eq 443 (30 matches) 30 deny ip any any (5 matches) Based on this output, what is the problem?
mediumWhy A: Option A is correct because the ACL explicitly permits TCP traffic from the 192.168.1.0/24 network to any destination on port 80, as shown by the first entry with 50 matches. The output confirms that this traffic is being allowed, so there is no problem with that specific rule.
Variation 2. Consider the following partial configuration on router R1: ``` interface GigabitEthernet0/1 ip access-group MY_ACL in ! ip access-list extended MY_ACL permit tcp 10.1.1.0 0.0.0.255 any eq 80 permit icmp any any echo deny ip any any ``` What is the effect of this ACL when applied inbound on GigabitEthernet0/1?
mediumWhy A: The ACL is applied inbound on GigabitEthernet0/1. The first permit statement allows TCP traffic from source network 10.1.1.0/24 to any destination on port 80 (HTTP). The second permit statement allows ICMP Echo requests (type 8) from any source. The final deny statement blocks all other IP traffic. Therefore, only HTTP requests from 10.1.1.0/24 and ICMP Echo requests from any source are permitted; all other IP traffic is denied.
Variation 3. Examine the following configuration: ``` interface GigabitEthernet0/3 ip access-group WEB_ONLY out ! ip access-list extended WEB_ONLY permit tcp any any eq 80 permit tcp any any eq 443 ``` What is the effect of this ACL when applied outbound on GigabitEthernet0/3?
mediumWhy B: The ACL named WEB_ONLY explicitly permits TCP traffic destined for ports 80 (HTTP) and 443 (HTTPS). When applied outbound on GigabitEthernet0/3, it filters traffic leaving the interface. Since every ACL has an implicit deny any at the end, only HTTP and HTTPS traffic is permitted outbound; all other traffic is denied.
Variation 4. Examine the following configuration snippet: ``` interface GigabitEthernet0/0 ip access-group BLOCK_TELNET out ! ip access-list extended BLOCK_TELNET deny tcp any any eq 23 permit ip any any ``` What is the effect of applying this ACL outbound on GigabitEthernet0/0?
mediumWhy B: The ACL is applied outbound on GigabitEthernet0/0, meaning it filters traffic as it leaves the interface. The first rule denies TCP traffic destined for port 23 (Telnet), and the second rule permits all other IP traffic. Therefore, Telnet sessions initiated from inside the network and exiting this interface are blocked, while all other traffic is allowed.
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Last reviewed: Jun 24, 2026
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