The answer is to configure the `ipv6 address 2001:db8:1:10::/64 eui-64` command on R1’s GigabitEthernet0/0 interface. This is correct because EUI-64 automatically generates the interface identifier from the interface’s MAC address, ensuring a unique, stateless IPv6 address without manual assignment. On the CCNA 200-301 v2 exam, this tests your ability to implement IPv6 connectivity across a Layer 3 switch, where missing an address on a router interface is a common troubleshooting point—R2 and MLS1 were already configured, but R1 lacked an IPv6 address entirely. A frequent trap is forgetting that EUI-64 requires the `/64` prefix length to work, or confusing it with static addressing; always verify the interface mode before applying the command. Memory tip: think “EUI-64 = MAC plus FF:FE in the middle” to recall how the 64-bit interface ID is derived.
CCNA Network Infrastructure and Connectivity Practice Question
This 200-301 practice question tests your understanding of network infrastructure and connectivity. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Network Topology
You are connected to R1 via console. The network consists of R1, R2, and a multilayer switch MLS1. R1's GigabitEthernet0/0 connects to MLS1's GigabitEthernet1/0/1 (VLAN 10), and MLS1's GigabitEthernet1/0/2 connects to R2's GigabitEthernet0/0. The goal is to enable IPv6 communication between R1 and R2 across the layer-3 switch. Currently, R1 and R2 cannot ping each other's IPv6 addresses. Configure R1's G0/0 with the IPv6 prefix 2001:db8:1:10::/64 using EUI-64, and R2's G0/0 with static IPv6 address 2001:db8:1:10::2/64. Also ensure MLS1 has IPv6 routing enabled and an IPv6 address on VLAN 10 (2001:db8:1:10::3/64). Troubleshoot and fix any layer-2 or layer-3 issues preventing connectivity.
R1# show running-config interface gigabitEthernet 0/0
Building configuration...
Current configuration : 123 bytes
!
interface GigabitEthernet0/0
ip address 192.168.10.1 255.255.255.0
duplex auto
speed auto
media-type rj45
end
R1# show ipv6 interface brief
GigabitEthernet0/0 [up/up]
unassigned
R2# show running-config interface gigabitEthernet 0/0
Building configuration...
Current configuration : 131 bytes
!
interface GigabitEthernet0/0
ip address 192.168.10.2 255.255.255.0
ipv6 address 2001:db8:1:10::2/64
duplex auto
speed auto
media-type rj45
end
MLS1# show running-config | section interface Vlan10
interface Vlan10
ip address 192.168.10.3 255.255.255.0
ipv6 address 2001:db8:1:10::3/64
!
MLS1# show ipv6 route
IPv6 Routing Table - default - 2 entries
Codes: C - Connected, L - Local, S - Static, R - RIP, B - BGP
U - Per-user Static route, M - MIPv6, I - Nemo
O - OSPF, IA - OSPF inter area, N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
D - EIGRP, EX - EIGRP external, ND - Neighbor Discovery
NDp - ND prefix, l - LISP
C 2001:db8:1:10::/64 [0/0]
via Vlan10, directly connected
L 2001:db8:1:10::3/128 [0/0]
via Vlan10, receive
R2# ping 2001:db8:1:10::3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:db8:1:10::3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5)
R1# ping 2001:db8:1:10::3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:db8:1:10::3, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
R1# ping 2001:db8:1:10::2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:db8:1:10::2, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
A
Configure 'ipv6 address 2001:db8:1:10::/64 eui-64' on R1's G0/0 interface.
The correct command uses only the prefix—not a specific interface ID—along with the eui-64 keyword. The router generates the interface ID from its MAC address, producing a unique global unicast address on the required subnet. This matches the requirement to use EUI-64 for R1's configuration.
B
Enable IPv6 routing on R1 with 'ipv6 unicast-routing'.
Why wrong: This is incorrect because R1 already has IPv6 routing enabled (as indicated by the connected route). The issue is the missing IPv6 address on the interface, not routing.
C
Configure 'ipv6 address 2001:db8:1:10::1/64' on R1's G0/0 interface (without EUI-64).
Why wrong: This is incorrect because the question explicitly requires the use of EUI-64. Using a static address without EUI-64 does not meet the requirement.
D
Change the VLAN on MLS1's G1/0/1 to match R1's VLAN.
Why wrong: This is incorrect because the interface is already in VLAN 10, which matches the subnet. The issue is not a VLAN mismatch but the missing IPv6 address on R1.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure 'ipv6 address 2001:db8:1:10::/64 eui-64' on R1's G0/0 interface.
R1 has no IPv6 address configured on G0/0. The required prefix is 2001:db8:1:10::/64 using EUI-64, which generates the interface ID from the MAC address. The command 'ipv6 address 2001:db8:1:10::/64 eui-64' must be entered in interface configuration mode. Additionally, MLS1 has IPv6 routing enabled (as seen by the connected route), but R1's interface is missing the IPv6 address. After configuration, R1 will be able to ping R2 and MLS1. No other changes are needed because R2 and MLS1 are correctly configured.
Key principle: Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Configure 'ipv6 address 2001:db8:1:10::/64 eui-64' on R1's G0/0 interface.
Why this is correct
The correct command uses only the prefix—not a specific interface ID—along with the eui-64 keyword. The router generates the interface ID from its MAC address, producing a unique global unicast address on the required subnet. This matches the requirement to use EUI-64 for R1's configuration.
Related concept
Authentication checks who the user is.
✗
Enable IPv6 routing on R1 with 'ipv6 unicast-routing'.
Why it's wrong here
This is incorrect because R1 already has IPv6 routing enabled (as indicated by the connected route). The issue is the missing IPv6 address on the interface, not routing.
✗
Configure 'ipv6 address 2001:db8:1:10::1/64' on R1's G0/0 interface (without EUI-64).
Why it's wrong here
This is incorrect because the question explicitly requires the use of EUI-64. Using a static address without EUI-64 does not meet the requirement.
✗
Change the VLAN on MLS1's G1/0/1 to match R1's VLAN.
Why it's wrong here
This is incorrect because the interface is already in VLAN 10, which matches the subnet. The issue is not a VLAN mismatch but the missing IPv6 address on R1.
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.
✓Configure 'ipv6 address 2001:db8:1:10::/64 eui-64' on R1's G0/0 interface.Correct answer▾
Why this is correct
The correct command uses only the prefix—not a specific interface ID—along with the eui-64 keyword. The router generates the interface ID from its MAC address, producing a unique global unicast address on the required subnet. This matches the requirement to use EUI-64 for R1's configuration.
✗Enable IPv6 routing on R1 with 'ipv6 unicast-routing'.Wrong answer — click to see why▾
Why this is wrong here
IPv6 unicast-routing is already enabled; the problem is at the interface level.
Why candidates choose this
Candidates often assume that IPv6 routing must be enabled globally, but in this scenario it is already configured.
✗Configure 'ipv6 address 2001:db8:1:10::1/64' on R1's G0/0 interface (without EUI-64).Wrong answer — click to see why▾
Why this is wrong here
The requirement specifies EUI-64; omitting it results in a static address that does not match the intended configuration.
Why candidates choose this
Candidates might think a static address is sufficient, but the question mandates EUI-64.
✗Change the VLAN on MLS1's G1/0/1 to match R1's VLAN.Wrong answer — click to see why▾
Why this is wrong here
The VLAN configuration is correct; no change is needed.
Why candidates choose this
Candidates might suspect a layer-2 issue, but the problem is at layer 3 on R1.
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?”
Common exam traps
Common exam trap: authentication is not authorization
Logging in proves the user can authenticate. It does not automatically mean the user is allowed to enter privileged or configuration mode. Watch for AAA authorization, privilege level and command authorization details.
Detailed technical explanation
How to think about this question
This kind of question is testing the difference between identity and permission. A user may successfully log in to a router because authentication is working, but still fail to enter configuration mode because authorization is missing, misconfigured or mapped to a lower privilege level.
KKey Concepts to Remember
Authentication checks who the user is.
Authorization controls what the user is allowed to do after login.
Privilege levels affect access to EXEC and configuration commands.
AAA, TACACS+ and RADIUS can separate login success from command access.
TExam Day Tips
→Do not assume successful login means full administrative access.
→Look for words such as cannot enter configuration mode, privilege level, authorization or command access.
→Separate login problems from permission problems before choosing the answer.
Key takeaway
Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related 200-301 questions on access control and AAA configuration.
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — Authentication checks who the user is..
What is the correct answer to this question?
The correct answer is: Configure 'ipv6 address 2001:db8:1:10::/64 eui-64' on R1's G0/0 interface. — R1 has no IPv6 address configured on G0/0. The required prefix is 2001:db8:1:10::/64 using EUI-64, which generates the interface ID from the MAC address. The command 'ipv6 address 2001:db8:1:10::/64 eui-64' must be entered in interface configuration mode. Additionally, MLS1 has IPv6 routing enabled (as seen by the connected route), but R1's interface is missing the IPv6 address. After configuration, R1 will be able to ping R2 and MLS1. No other changes are needed because R2 and MLS1 are correctly configured.
What should I do if I get this 200-301 question wrong?
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related 200-301 questions on access control and AAA configuration.
What is the key concept behind this question?
Authentication checks who the user is.
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