Use the show interfaces serial command to verify proper configuration of HDLC or PPP encapsulation. The command output in Figure 1 shows a PPP configuration.
When you configure HDLC, the output of the show interfaces serial command should display encapsulation HDLC. When PPP is configured, the LCP and NCP states also display. Notice that NCPs IPCP and IPV6CP are open for IPv4 and IPv6 because R1 and R2 were configured with both IPv4 and IPv6 addresses.
Figure 2 summarizes commands used when verifying PPP.
The show ppp multilink command verifies that PPP multilink is enabled on R3, as shown in Figure 3. The output indicates the interface Multilink 1, the hostnames of both the local and remote endpoints, and the serial interfaces assigned to the multilink bundle.