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DHCP Lease Monitor System
Created on March 13, 2026
The DHCP Lease Monitor is a critical component responsible for receiving lease updates from external DHCP clients and routing them to the appropriate processing handlers. It implements an Inter-Process Communication (IPC) system using nanomsg library to ensure reliable and efficient message passing between DHCP client plugins and the DHCP Manager.
Architecture
The lease monitor operates as a separate thread within the DHCP Manager process and implements a producer-consumer pattern:
┌─────────────────────┐ ┌─────────────────────┐ ┌─────────────────────┐ │ DHCP Clients │────►│ Lease Monitor │────►│ Lease Handlers │ │ │ │ │ │ │ │ • udhcpc (DHCPv4) │ │ • IPC Server │ │ • DHCPv4 Handler │ │ • dibbler (DHCPv6) │ │ • Message Router │ │ • DHCPv6 Handler │ │ • Plugin Execution │ │ • Quick Processing │ │ • TR-181 Updates │ └─────────────────────┘ └─────────────────────┘ └─────────────────────┘
Key Components
Files
- Source:
source/DHCPMgrUtils/dhcp_lease_monitor_thrd.c - Header:
source/DHCPMgrUtils/dhcp_lease_monitor_thrd.h
Core Functions
DhcpMgr_LeaseMonitor_Start()
- Purpose: Initializes and starts the lease monitor service
- Returns: 0 on success, -1 on failure
- Threading: Creates a new detached thread for monitoring
DhcpMgr_LeaseMonitor_Init()
- Purpose: Sets up the IPC socket and binds to the listening address
- Protocol: Uses nanomsg NN_PULL socket for receiving messages
- Address:
tcp://127.0.0.1:50324
DhcpMgr_LeaseMonitor_Thrd()
- Purpose: Main monitoring loop that processes incoming lease messages
- Behavior: Runs continuously until system shutdown
- Processing: Validates and routes messages based on DHCP version
Message Protocol
Message Structure
typedef struct {
char ifname[BUFLEN_32]; // Interface name (e.g., "erouter0")
DHCP_SOURCE version; // DHCP_VERSION_4 or DHCP_VERSION_6
union {
DHCPv4_PLUGIN_MSG dhcpv4; // DHCPv4 lease information
DHCPv6_PLUGIN_MSG dhcpv6; // DHCPv6 lease information
} data;
} PLUGIN_MSG;
DHCP Version Enumeration
typedef enum {
DHCP_VERSION_4, // DHCPv4 lease message
DHCP_VERSION_6, // DHCPv6 lease message
} DHCP_SOURCE;
DHCPv4 Message Format
The DHCPv4 plugin message contains:
- IP address assignment information
- DHCP server details
- Lease timing information
- Gateway and DNS server data
- Custom DHCP options
DHCPv6 Message Format
The DHCPv6 plugin message contains:
- IANA (Identity Association for Non-temporary Addresses) information
- IAPD (Identity Association for Prefix Delegation) information
- Lease timing parameters
- DNS server configuration
- Custom DHCPv6 options
IPC Implementation Details
Transport Protocol
- Library: nanomsg
- Pattern: Pipeline (NN_PULL socket)
- Address:
tcp://127.0.0.1:50324 - Benefits:
- Automatic message queuing
- Built-in reliability
- Language-agnostic protocol
- Scalable message passing
Message Flow
- Client Plugin: DHCP client executes plugin binary on lease events
- Plugin Execution: Plugin creates nanomsg NN_PUSH socket
- Message Send: Plugin sends PLUGIN_MSG structure to monitor
- Monitor Receive: Lease monitor receives message via NN_PULL socket
- Validation: Monitor validates message size and structure
- Routing: Monitor routes message to appropriate handler based on version
- Processing: Handler processes lease and updates system state
Error Handling
The monitor implements robust error handling:
bytes = nn_recv(ipcListenFd, (PLUGIN_MSG *)&plugin_msg, msg_size, 0);
if (bytes == msg_size) {
// Valid message - process normally
} else if (bytes < 0) {
DHCPMGR_LOG_ERROR("Failed to receive message from IPC");
} else {
DHCPMGR_LOG_ERROR("Message size unexpected");
}
Thread Safety and Concurrency
Thread Model
- Main Thread: Handles TR-181 operations and client management
- Monitor Thread: Dedicated to IPC message processing
- Handler Threads: Process leases asynchronously
Synchronization
- Lock-free Design: Monitor thread operates independently
- Memory Management: Each message allocates separate memory for handlers
- Cleanup: Automatic cleanup on thread termination
Performance Characteristics
- Low Latency: Immediate message processing
- High Throughput: Efficient message queuing
- Minimal Blocking: Non-blocking message reception
- Resource Efficient: Single thread handles all interfaces
Integration Points
DHCP Client Plugins
udhcpc Plugin
- Location:
source/DHCPClientUtils/DHCPv4Client/dhcpmgr_udhcpc_plugin/ - Execution: Called by udhcpc on lease events
- Message: Sends DHCPv4_PLUGIN_MSG via IPC
dibbler Plugin
- Location:
source/DHCPClientUtils/DHCPv6Client/dhcpmgr_dibbler_plugin/ - Execution: Called by dibbler on lease events
- Message: Sends DHCPv6_PLUGIN_MSG via IPC
Lease Handlers
DHCPv4 Handler
- Function:
DHCPMgr_AddDhcpv4Lease() - Processing: Updates TR-181 model, configures interface
- Location: Controller manages lease processing
DHCPv6 Handler
- Function:
DHCPMgr_AddDhcpv6Lease() - Processing: Handles IANA/IAPD, updates model
- Location: Controller manages lease processing
Configuration
Socket Configuration
#define DHCP_MANAGER_ADDR "tcp://127.0.0.1:50324"
Buffer Sizes
#define BUFLEN_32 32 // Interface name buffer
Message Size
int msg_size = sizeof(PLUGIN_MSG); // Fixed message size
Monitoring and Debugging
Log Messages
The monitor provides detailed logging:
- Initialization success/failure
- Message reception status
- Processing decisions
- Error conditions
Debug Information
- Interface name for each lease
- Message size validation
- DHCP version identification
- Processing time tracking
Common Issues
- Socket Binding Failure
- Check if port 50324 is available
- Verify network interface status
- Check firewall settings
- Message Size Mismatch
- Verify plugin and monitor use same structures
- Check for structure padding issues
- Validate nanomsg library versions
- Plugin Execution Failure
- Verify plugin binary permissions
- Check plugin executable path
- Validate DHCP client configuration
Performance Optimization
Memory Management
- Pre-allocated Structures: Use fixed-size message structures
- Immediate Processing: Process messages quickly to avoid queuing
- Cleanup: Proper memory cleanup in handlers
Network Optimization
- Local IPC: Uses localhost to minimize network overhead
- Binary Protocol: Efficient binary message format
- Minimal Serialization: Direct structure copying
Threading Optimization
- Dedicated Thread: Separate thread for IPC operations
- Non-blocking Operations: Avoid blocking main controller
- Detached Thread: Automatic resource cleanup
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