easyMultiple ChoiceObjective-mapped
300-410 Practice Question: Runs the following command on Router R1: R1# show…
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?
⚠ Common exam trap
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.
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
✓
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.
Answer analysis
Option-by-option breakdown
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.
- ✗
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.
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Same concept, more angles
4 more ways this is tested on 300-410
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?
medium- ✓ A.Traffic from 192.168.1.0/24 to port 80 is permitted.
- B.Traffic from 192.168.2.0/24 to port 443 is denied.
- C.All traffic from 192.168.1.0/24 is permitted.
- D.The ACL is correctly configured to allow only specific web traffic.
Why A: 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?
medium- ✓ A.It permits HTTP requests from 10.1.1.0/24 and ICMP Echo requests from any source; all other IP traffic is denied.
- B.It permits HTTP requests from 10.1.1.0/24 and all ICMP traffic; all other IP traffic is denied.
- C.It permits HTTP requests from any source to 10.1.1.0/24 and ICMP Echo requests; all other traffic is denied.
- D.It permits HTTP requests from 10.1.1.0/24 and ICMP Echo replies; all other IP traffic is denied.
Why 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?
medium- A.It permits all web traffic entering the interface.
- ✓ B.It permits only HTTP and HTTPS traffic to leave the interface; all other traffic is denied.
- C.It permits all TCP traffic to any destination.
- D.It has no effect because the ACL is missing a deny statement.
Why 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?
medium- A.It blocks Telnet traffic entering the interface from the network.
- ✓ B.It blocks Telnet traffic leaving the interface, but permits all other IP traffic.
- C.It permits Telnet traffic and blocks all other IP traffic.
- D.It has no effect because the ACL is missing a sequence number.
Why 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.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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