Routers R2 and R4 are directly connected on their serial1 interfaces using a DTE / DCE cable. R2 is using HDLC encapsulation and R4 is using PPP. David runs a “show interface serial1” on both of the routers. What will be the command output show?
Explanation
Answer: B - IF you run the “show interface serial1” command on two routers using HDLC encapsulation and PPP, a message is displayed, stating, “Serial 1 is administratively down, line protocol is down.”
Key Takeaway: HDLC is a layer-2 protocol used to connect point-to-point serial devices. It requires the least amount of configuration to connect these two locations. Point-to-Point Protocol, or PPP, is used for dial-up connection to the Internet. It is based on HDLC and is very similar. However, if two routers are using different encapsulation standards, the physical interface will show as “up” and the line protocol will show as “down.”
