Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
Exhibit
R1# interface Serial0/0/0 encapsulation ppp ppp chap hostname Branch1 ppp chap password cisco123 R2# interface Serial0/0/0 encapsulation ppp ppp chap hostname Branch1 ppp chap password cisco321
Based on the exhibit, what is the most likely reason the PPP link is failing to authenticate?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Best answer
The PPP authentication credentials do not match between the two sides.
This is correct because the CHAP passwords shown are different.
B
Distractor review
The interfaces must use HDLC instead of PPP before authentication can work.
This is wrong because PPP is exactly the encapsulation associated with this authentication scenario.
C
Distractor review
CHAP requires the routers to be in different IPv4 subnets.
This is wrong because subnet mismatch is not the issue shown here.
D
Distractor review
PPP authentication works only over GRE tunnels.
This is wrong because GRE is unrelated to basic PPP CHAP authentication.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is to assume that authentication issues are due to interface encapsulation or IP addressing. Here, options B, C, and D distract by mentioning HDLC, subnet mismatches, or GRE tunnels, which are unrelated to PPP CHAP authentication. The key is to focus on credential matching, as PPP CHAP requires identical usernames and passwords on both ends to succeed.
Technical deep dive
How to think about this question
PPP (Point-to-Point Protocol) supports authentication protocols like PAP and CHAP to validate peers before establishing a link. CHAP (Challenge Handshake Authentication Protocol) uses a three-way handshake where one router challenges the other to prove its identity using a shared secret password. Both routers must have matching CHAP usernames and passwords configured. If the credentials differ, the authentication fails, preventing the logical link from coming up despite the physical interface being operational. This is a common issue in WAN links where misconfigured passwords or usernames cause authentication failures. Unlike HDLC, which does not support authentication, PPP is designed to handle authentication natively. Also, CHAP does not depend on IP subnetting or GRE tunnels; it operates at the data link layer. Understanding this helps isolate authentication problems from other link or routing issues.
KKey Concepts to Remember
- PPP CHAP authentication requires matching credentials
- PPP supports authentication unlike HDLC
- Authentication failure occurs despite physical link being up
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.
Related practice questions
Related 200-301 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
CCNA subnetting practice questions
Practise IPv4 subnetting, CIDR, masks, host ranges and subnet selection.
CCNA OSPF practice questions
Practise OSPF neighbours, router IDs, metrics, areas and routing-table interpretation.
CCNA VLAN practice questions
Practise VLANs, access ports, trunks, allowed VLANs and switching scenarios.
CCNA STP practice questions
Practise spanning tree, root bridge election, port roles and STP troubleshooting.
CCNA EtherChannel practice questions
Practise LACP, PAgP, port-channel behaviour and bundle requirements.
CCNA ACL practice questions
Practise standard and extended ACLs, permit/deny logic and traffic filtering.
CCNA NAT practice questions
Practise static NAT, dynamic NAT, PAT and inside/outside address translation.
CCNA DHCP practice questions
Practise DHCP scopes, relay, leases and troubleshooting.
CCNA show ip route practice questions
Practise routing-table output, longest-prefix match, AD and route selection.
CCNA show interfaces trunk practice questions
Practise trunk verification and VLAN forwarding across switches.
CCNA wireless security practice questions
Practise WLAN security, authentication and wireless architecture concepts.
CCNA IPv6 practice questions
Practise IPv6 addressing, routes, neighbour discovery and common IPv6 exam traps.
More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
PPP CHAP authentication requires matching credentials
What is the correct answer to this question?
The correct answer is: The PPP authentication credentials do not match between the two sides. — The most likely reason is a credentials mismatch between the two sides of the PPP authentication setup. In practical terms, PPP authentication requires the peers to agree on the relevant identity and secret information. If those values do not align, the link may come up physically but authentication fails and the logical connection does not establish properly. This is a very exam-relevant WAN troubleshooting scenario because it focuses on a realistic failure after the transport is already present.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
Discussion
Loading comments…
Sign in to join the discussion.