Exam 200-105 topic 1 question 86 discussion

Instructions -
- Enter Cisco IOS commands on device to verify network operation and answer for multiple-choice questions.
- THIS TASK DOES NOT REQUIRE DEVICE CONFIGURATION.
- Click the device icon to gain access to the console of the router. No console or enable passwords are required.
- To access the multiple-choice questions, click the numbered boxes on the left of the top panel.
- This task has four multiple-choice questions. Be sure to answer all four questions before clicking the Next button.

Scenario -
You are implementing PPP over serial links between R1 router and branch offices. In Phase 1 you must implement and verify PPP and GRE tunnel configurations as mentioned in the topology. In Phase 2 your colleague is expected to do NAT and ISP configurations between R1 and ISP router.
Identify the issues that you encounter during PPP over serial links implementation.
Routers Branch1, Branch2, and Branch3 connect to Router R1 in the main office over serial links.
PPP multilink implementation is recommended between R1 and Branch1 routers.
The GRE tunnel is configured between R2 and Branch2 routers, and traffic between Server farm1 10.10.10.0/24 network and Branch2 LAN 10.10.20.0/24 network, is routed over GRE tunnel using static route.
You have console access on R1, R2, Branch1, Branch2, and Branch3 devices. Use only show commands to troubleshoot the issues.

Why has the Branch3 router lost connectivity with R1?
Use only show commands to troubleshoot because usage of the debug command is restricted on the Branch3 and R1 routers.

Suggested Answer: A 🗳️
First we should check Branch3 (and R1) with the "show ip interface brief" command to find any Layer1/Layer 2 issue.

We see the interfaces connecting between them are in "up/down" states which indicates an Layer 2 issue so we should check the configuration of these interfaces carefully with the "show running-config" command and pay attention to these interfaces.
and on Branch3:

We learn from above config is R1 is using CHAP to authenticate Branch3 router (via the "ppp authentication chap" command on R1). Branch3 router is sending
CHAP hostname "Branch_3" and CHAP password "Branch3_Secret!" to R1 to be authenticated. Therefore we should check if R1 has already been configured with such username and password or not with the "show running-config" command on R1:

On R1 we see the configured username is "Branch3", not "Branch_3" so the usernames here are mismatched and this is the problem -> Answer A is correct.