Swatantra-66 opened a new pull request, #20513:
URL: https://github.com/apache/nuttx/pull/20513
## Summary
Addresses #11081.
Provides a comprehensive, production-grade documentation guide for the
`dhcpc` (Dynamic Host Configuration Protocol client) network utility in
`Documentation/applications/netutils/dhcpc/index.rst`, replacing the previous
7-line placeholder stub.
### Content Included
- **Protocol Architecture & State Machine**: Details RFC 2131 (IPv4) and RFC
1542 (BOOTP interoperability), mapping the 6-stage lifecycle (`INIT`,
`SELECTING`, `REQUESTING`, `BOUND`, `RENEWING`/`REBINDING`, and `RELEASE`).
- **Security Considerations**: Documents vulnerabilities inherent to
unauthenticated plaintext DHCPv4, rogue DHCP server risks, and mitigations
(DHCP Snooping, Port Security, end-to-end transport encryption).
- **Requirements & Prerequisites**: Lists networking dependencies including
`CONFIG_NET_BROADCAST=y` (required for `DHCPDISCOVER` broadcast traffic) and
`CONFIG_NET_BINDTODEVICE=y`.
- **Configuration Reference**: Complete Kconfig options table
(`CONFIG_NETUTILS_DHCPC`, hostname, timeouts, retries, BOOTP broadcast flags,
NTP/DNS server counts, and release transmission delays).
- **NSH Integration**: Runtime commands (`ifconfig <ifname> dhcp`) and
network verification (`ifconfig`, `ping`).
- **C API Reference**: Detailed specification of `struct dhcpc_state` and
core lifecycle functions with POSIX `ERROR`/`errno` return contracts
(`dhcpc_open`, `dhcpc_request`, `dhcpc_request_async`, `dhcpc_release`,
`dhcpc_cancel`, `dhcpc_close`).
- **Runnable Application Examples**:
1. Synchronous IP acquisition flow querying hardware MAC via `netlib`,
performing DHCP negotiation, and applying IP/netmask/router/DNS parameters to
the stack.
2. Graceful lease release before system reboot or link teardown.
- **Embedded Design Guidelines**: Lease renewal timer scheduling ($T_1$) for
long-running IoT devices, wireless retransmission tuning, and `SO_BINDTODEVICE`
multihomed operation.
## Impact
- Closes the missing documentation stub for `dhcpc` under #11081.
- Completes the core network client trilogy (`webclient`, `tftpc`, `dhcpc`)
for Apache NuttX documentation.
## Testing
- Verified reStructuredText syntax, formatting, and table alignment.
- Confirmed zero trailing whitespaces across all 430+ lines.
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