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300-410 Practice Question: In a standard IPv4 ACL, what is the default…
In a standard IPv4 ACL, what is the default wildcard mask if none is explicitly configured?
⚠ Common exam trap
Cisco often tests the misconception that a missing wildcard mask defaults to 'any' (255.255.255.255) or that the mask is mandatory, when in fact the default is a host match (0.0.0.0).
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
✓
0.0.0.0 (host match)
In a standard IPv4 ACL, if no wildcard mask is explicitly configured, the default wildcard mask is 0.0.0.0, which means the ACL matches only the exact source IP address (a host match). This is because the access-list command treats the source address as a host address when no mask is provided, effectively applying a host wildcard mask.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
0.0.0.0 (host match)
Why this is correct
When no wildcard mask is given, the router assumes a host match.
- ✗
255.255.255.255 (any match)
Why it's wrong here
That would match all addresses, but it is not the default.
- ✗
The mask is mandatory; configuration is rejected without it.
Why it's wrong here
IOS accepts the command without mask and defaults to host match.
- ✗
The mask is derived from the source address class.
Why it's wrong here
No classful derivation occurs; it defaults to host.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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