pppdump

pppdump [options] [expression]

-i interface
    Listen on interface for PPP packets. Defaults to the first PPP interface found.

-f file
    Read PPP packets from file. This file should contain raw PPP frames.

-dd
    Increase verbosity.

-v
    Print version and exit.

[expression]
    A tcpdump-style filter expression to select which packets to analyze.

pppdump is a tool used to analyze and display the contents of Point-to-Point Protocol (PPP) packets. It captures PPP frames from a specified interface or input file and interprets them, presenting the information in a human-readable format.

This command is invaluable for debugging PPP connections, troubleshooting network issues, and understanding the PPP protocol structure. It decodes various PPP control protocols (like LCP, NCP, IPCP, etc.) and data protocols (like IP, IPv6, etc.), providing details about the packet headers, options, and payload. pppdump is a passive tool, meaning it only observes and interprets packets; it doesn't modify or interfere with the network traffic.

pppdump requires root privileges to capture packets from network interfaces. It may not decode all PPP extensions or protocols perfectly.

pppdump utilizes a similar expression syntax to tcpdump for filtering packets. Common filters include protocol types (e.g., 'ip', 'ipv6', 'lcp'), interface names (e.g., 'ppp0'), and host addresses.

pppdump has been around for a long time, initially developed alongside the pppd daemon to aid in debugging and network analysis during the early days of widespread dial-up internet access. It was crucial for troubleshooting PPP connections and understanding the protocol's behavior. As broadband technologies replaced dial-up, pppdump's direct usage decreased, but it remained a valuable tool in certain embedded systems and specialized network environments that continue to rely on PPP. Development is slow but it is available in most common linux distributions

tcpdump(1), wireshark(1)