CCNA Network Services and Security Practice Question
Exhibit
R1# show running-config | section interface GigabitEthernet0/1
interface GigabitEthernet0/1
ip address 192.168.10.1 255.255.255.0
ip access-group BLOCK_SMTP in
duplex auto
speed auto
!
R1# show access-lists BLOCK_SMTP
Extended IP access list BLOCK_SMTP
10 deny tcp any any eq 25
20 permit ip any anyYou are connected to R1 via the console. An extended ACL named BLOCK_SMTP has been applied inbound on interface GigabitEthernet0/1, but users on the 192.168.10.0/24 network cannot send email to the SMTP server at 203.0.113.10. Additionally, the ACL is blocking all other traffic that should be permitted. Examine the running configuration and fix the ACL so that SMTP traffic (TCP port 25) from the 192.168.10.0/24 network to the SMTP server is permitted, and all other IP traffic is allowed.
⚠ Common exam trap
Remember that ACLs are processed sequentially; the first match wins. A common mistake is to place a general permit or deny before a specific statement, causing the specific statement to never be evaluated. Always order ACL entries from most specific to most general.
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
✓
permit tcp 192.168.10.0 0.0.0.255 host 203.0.113.10 eq 25 deny tcp any any eq 25 permit ip any any
It permits SMTP from 192.168.10.0/24 to the SMTP server, then denies all other SMTP traffic, and finally permits all other IP traffic. Option B is wrong because it places a general permit for any SMTP before the specific deny, meaning all SMTP is permitted regardless of source/destination. Option C is wrong because it denies all SMTP first, so the subsequent specific permit for the user network is never reached. Option D is wrong because the order permits the specific SMTP, then permits all IP traffic (including other SMTP), then denies SMTP—the permit ip any any before the deny makes the deny unreachable for all traffic, allowing all SMTP.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
permit tcp 192.168.10.0 0.0.0.255 host 203.0.113.10 eq 25 deny tcp any any eq 25 permit ip any any
Why this is correct
This sequence correctly permits SMTP from the specific source to the specific destination, then denies all other SMTP, and finally permits all other IP traffic. The order ensures that the desired SMTP traffic is allowed before the general deny, and the permit ip any any at the end allows all non-SMTP traffic.
- ✗
permit tcp any any eq 25 deny tcp 192.168.10.0 0.0.0.255 host 203.0.113.10 eq 25 permit ip any any
Why it's wrong here
This is incorrect because it permits all SMTP traffic first, then denies the specific SMTP traffic, which has no effect since the permit any any already allows it. The deny line is never reached for that traffic.
- ✗
deny tcp any any eq 25 permit tcp 192.168.10.0 0.0.0.255 host 203.0.113.10 eq 25 permit ip any any
Why it's wrong here
Placing 'deny tcp any any eq 25' first is fatal because ACLs are evaluated top-down and the first match wins. Any SMTP packet (destination port 25) from any source, including the desired 192.168.10.0/24 to 203.0.113.10 traffic, will match this broad deny rule immediately and be dropped. The subsequent specific permit line is never evaluated for that traffic, so the permit becomes a dead entry that can only affect non-SMTP packets, which are already covered by the final 'permit ip any any'.
- ✗
permit tcp 192.168.10.0 0.0.0.255 host 203.0.113.10 eq 25 permit ip any any deny tcp any any eq 25
Why it's wrong here
This is incorrect because the permit ip any any at the end allows all IP traffic, including SMTP from other sources, before the deny tcp any any eq 25 is reached. The deny line becomes useless.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓permit tcp 192.168.10.0 0.0.0.255 host 203.0.113.10 eq 25 deny tcp any any eq 25 permit ip any anyCorrect answer▾
Why this is correct
This sequence correctly permits SMTP from the specific source to the specific destination, then denies all other SMTP, and finally permits all other IP traffic. The order ensures that the desired SMTP traffic is allowed before the general deny, and the permit ip any any at the end allows all non-SMTP traffic.
✗permit tcp any any eq 25 deny tcp 192.168.10.0 0.0.0.255 host 203.0.113.10 eq 25 permit ip any anyWrong answer — click to see why▾
Why this is wrong here
The order of ACL entries is crucial; the first match is applied. Here, the permit any any matches all SMTP before the deny can block the specific traffic.
Why candidates choose this
Candidates may think that placing the deny after the permit will override it, but ACLs are processed top-down and the first match wins.
✗deny tcp any any eq 25 permit tcp 192.168.10.0 0.0.0.255 host 203.0.113.10 eq 25 permit ip any anyWrong answer — click to see why▾
Why this is wrong here
The deny any any matches all SMTP, so the subsequent permit for the specific source/destination is never reached.
Why candidates choose this
Candidates might think that a more specific permit can override a general deny, but ACLs are processed sequentially; the first match (deny) blocks the traffic.
✗permit tcp 192.168.10.0 0.0.0.255 host 203.0.113.10 eq 25 permit ip any any deny tcp any any eq 25Wrong answer — click to see why▾
Why this is wrong here
The permit ip any any matches all traffic, so the subsequent deny for SMTP is never applied.
Why candidates choose this
Candidates might think that placing the deny at the end will block SMTP, but the permit ip any any already permits everything, including SMTP.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
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Related to this question
Learn chapter
RA Guard — IPv6 First-Hop Security
Key term
SMTP
SMTP (Simple Mail Transfer Protocol) is the standard internet protocol used to send emails from a client to a server or between email servers.
Key term
Access Control List
An Access Control List is a set of rules that decides which traffic is allowed or denied entry to a network or device.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.