Question 677 of 2,152

IPv4 Access Control Lists →hardMultiple SelectObjective-mapped

Quick Answer

The answer is that the 'ip access-group' command can be applied to a VLAN interface (SVI) to filter traffic routed into or out of that VLAN. This is correct because an outbound ACL processes packets after the routing decision has been made and just before the packet exits the interface, meaning the router first determines the outgoing interface and next hop via its routing table, then applies the ACL to filter based on destination address and other criteria. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding of how ACLs interact with the routing process, often appearing in questions about SVI filtering or traffic flow order. A common trap is confusing inbound ACLs, which filter before routing, with outbound ACLs, which filter after routing—remember that outbound ACLs see the final destination IP, not the source. Memory tip: "Route first, then filter out" to recall that outbound ACLs apply post-routing.

300-410 IPv4 Access Control Lists Practice Question

This 300-410 practice question tests your understanding of ipv4 access control lists. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.

Which TWO statements about the 'ip access-group' command and its interaction with ACLs are correct? (Choose TWO.)

Question 1hardmulti select

Study the full ACL explanation →

A
An inbound ACL processes packets after the routing decision is made.
Why wrong: Incorrect. Inbound ACLs process packets before routing, so the router checks the ACL before deciding where to forward the packet.
B
An outbound ACL processes packets before they leave the interface, after the routing decision.
Correct. Outbound ACLs are applied after the router determines the outgoing interface and before the packet is transmitted.
C
The ACL referenced in the 'ip access-group' command must already exist in the configuration.
Correct. If the ACL does not exist, the command is rejected with an error indicating the ACL is not found.
D
The 'ip access-group' command can be applied to a Layer 2 switchport to filter IPv4 traffic.
Why wrong: Incorrect. On a Layer 2 switchport, VLAN ACLs (VACLs) or port ACLs (PACLs) are used; 'ip access-group' is only for Layer 3 interfaces.
E
The 'ip access-group' command can be applied to a VLAN interface (SVI) to filter traffic routed into or out of that VLAN.
Correct. SVIs are Layer 3 interfaces, so 'ip access-group' can be applied inbound or outbound to filter routed traffic.

Full breakdown with real-world context →

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

✓

An outbound ACL processes packets before they leave the interface, after the routing decision.

Option B is correct because an outbound ACL processes packets after the routing decision has been made and just before the packet exits the interface. This ensures that the router first determines the outgoing interface and next hop via its routing table, then applies the ACL to filter traffic based on the destination address and other criteria before forwarding.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
An inbound ACL processes packets after the routing decision is made.
Why it's wrong here
Incorrect. Inbound ACLs process packets before routing, so the router checks the ACL before deciding where to forward the packet.
✓
An outbound ACL processes packets before they leave the interface, after the routing decision.
Why this is correct
Correct. Outbound ACLs are applied after the router determines the outgoing interface and before the packet is transmitted.
Related concept
Read the scenario before looking for a memorised answer.
✓
The ACL referenced in the 'ip access-group' command must already exist in the configuration.
Why this is correct
Correct. If the ACL does not exist, the command is rejected with an error indicating the ACL is not found.
Related concept
Read the scenario before looking for a memorised answer.
✗
The 'ip access-group' command can be applied to a Layer 2 switchport to filter IPv4 traffic.
Why it's wrong here
Incorrect. On a Layer 2 switchport, VLAN ACLs (VACLs) or port ACLs (PACLs) are used; 'ip access-group' is only for Layer 3 interfaces.
✓
The 'ip access-group' command can be applied to a VLAN interface (SVI) to filter traffic routed into or out of that VLAN.
Why this is correct
Correct. SVIs are Layer 3 interfaces, so 'ip access-group' can be applied inbound or outbound to filter routed traffic.
Related concept
Read the scenario before looking for a memorised answer.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that an outbound ACL processes packets before routing, when in fact it processes after the routing decision, while an inbound ACL processes before routing.

Detailed technical explanation

How to think about this question

Under the hood, when an outbound ACL is applied, the router performs a route lookup to determine the exit interface and next hop, then evaluates the packet against the ACL entries in order until a match is found. A subtle behavior is that outbound ACLs on a router process locally generated packets (e.g., from the router itself) only if the ACL is applied to the outgoing interface and the packet is not originated by the router; for locally originated traffic, an outbound ACL does not apply—only inbound ACLs on the ingress interface or control-plane policing can filter it.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this 300-410 question test?

IPv4 Access Control Lists — This question tests IPv4 Access Control Lists — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: An outbound ACL processes packets before they leave the interface, after the routing decision. — Option B is correct because an outbound ACL processes packets after the routing decision has been made and just before the packet exits the interface. This ensures that the router first determines the outgoing interface and next hop via its routing table, then applies the ACL to filter traffic based on the destination address and other criteria before forwarding.

What should I do if I get this 300-410 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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Same concept, more angles

1 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. Which TWO configuration steps are required to apply an IPv4 extended access list to an interface in Cisco IOS? (Choose TWO.)

medium

✓ A.Configure the ACL using access-list or ip access-list commands.
✓ B.Apply the ACL to the interface with the ip access-group command.
C.Create the ACL directly under the interface configuration mode.
D.Use the access-class command on the interface.
E.Enable the ACL with the ip inspect command.

Why A: Option A is correct because an IPv4 extended ACL must first be defined using either the numbered `access-list` command or the named `ip access-list extended` command before it can be applied. Option B is correct because the `ip access-group` command is the only way to bind a configured ACL to an interface in Cisco IOS, specifying the direction (in or out) and optionally the VLAN filter.

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