hardMultiple ChoiceObjective-mapped
300-410 Practice Question: A network using IPv6 over IPv4 ISATAP tunnels is…
A network using IPv6 over IPv4 ISATAP tunnels is experiencing connectivity issues. Router R1 has the following relevant configuration: interface Tunnel0 ipv6 address 2001:DB8:1::/64 eui-64 tunnel source 192.0.2.1 tunnel mode ipv6ip isatap. Router R2 shows: R2# show ipv6 interface Tunnel0 Tunnel0 is up, line protocol is up IPv6 is enabled, link-local address is FE80::5EFE:192.0.2.2 Global unicast address(es): 2001:DB8:1::5EFE:192.0.2.2. What is the root cause?
⚠ Common exam trap
Cisco often tests the distinction between standard EUI-64 address generation and ISATAP's fixed interface identifier format, trapping candidates who assume that eui-64 is always correct for IPv6 tunnel interfaces.
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
✓
The tunnel mode should be ipv6ip isatap on both ends, but R2's address shows correct ISATAP format, indicating R1's address is wrong.
ISATAP tunnels require both endpoints to use the same tunnel mode (ipv6ip isatap) and to form the IPv6 interface identifier from the IPv4 tunnel source using the format ::5EFE:w.x.y.z. R2's global address 2001:DB8:1::5EFE:192.0.2.2 correctly embeds its IPv4 address 192.0.2.2, but R1's configuration with the eui-64 keyword causes it to derive an interface identifier from its MAC address instead of the required ISATAP format. This mismatch prevents proper IPv6 neighbor discovery and connectivity over the tunnel.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The IPv6 address on R1 should be configured without the eui-64 keyword to allow manual assignment.
Why it's wrong here
The issue is the address format, not the method of assignment.
- ✓
The tunnel mode should be ipv6ip isatap on both ends, but R2's address shows correct ISATAP format, indicating R1's address is wrong.
Why this is correct
R1's address uses EUI-64, which does not produce the ISATAP-specific interface identifier, causing address mismatch.
- ✗
The tunnel source on R1 should be the IPv4 address of R2.
Why it's wrong here
The tunnel source is the local IPv4 address, which is correct.
- ✗
ISATAP requires the use of a link-local address only.
Why it's wrong here
Global unicast addresses are also used in ISATAP.
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 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 300-410 exam.