diff --git a/go.mod b/go.mod
index 23af7d4..f12d66d 100644
--- a/go.mod
+++ b/go.mod
@@ -1,20 +1,23 @@
 module github.com/loveuer/go-alived
 
-go 1.25.0
+go 1.24.0
+
+require (
+	github.com/mdlayher/arp v0.0.0-20220512170110-6706a2966875
+	github.com/spf13/cobra v1.10.2
+	github.com/vishvananda/netlink v1.3.1
+	golang.org/x/net v0.47.0
+	gopkg.in/yaml.v3 v3.0.1
+)
 
 require (
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/josharian/native v1.0.0 // indirect
-	github.com/mdlayher/arp v0.0.0-20220512170110-6706a2966875 // indirect
 	github.com/mdlayher/ethernet v0.0.0-20220221185849-529eae5b6118 // indirect
 	github.com/mdlayher/packet v1.0.0 // indirect
 	github.com/mdlayher/socket v0.2.1 // indirect
-	github.com/spf13/cobra v1.10.2 // indirect
 	github.com/spf13/pflag v1.0.9 // indirect
-	github.com/vishvananda/netlink v1.3.1 // indirect
 	github.com/vishvananda/netns v0.0.5 // indirect
-	golang.org/x/net v0.47.0 // indirect
 	golang.org/x/sync v0.0.0-20210220032951-036812b2e83c // indirect
 	golang.org/x/sys v0.38.0 // indirect
-	gopkg.in/yaml.v3 v3.0.1 // indirect
 )
diff --git a/go.sum b/go.sum
index 5730267..4ef65df 100644
--- a/go.sum
+++ b/go.sum
@@ -1,5 +1,6 @@
 github.com/cpuguy83/go-md2man/v2 v2.0.6/go.mod h1:oOW0eioCTA6cOiMLiUPZOpcVxMig6NIQQ7OS05n1F4g=
 github.com/google/go-cmp v0.5.6/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/google/go-cmp v0.5.7 h1:81/ik6ipDQS2aGcBfIN5dHDB36BwrStyeAQquSYCV4o=
 github.com/google/go-cmp v0.5.7/go.mod h1:n+brtR0CgQNWTVd5ZUFpTBC8YFBDLK/h/bpaJ8/DtOE=
 github.com/inconshreveable/mousetrap v1.1.0 h1:wN+x4NVGpMsO7ErUn/mUI3vEoE6Jt13X2s0bqwp9tc8=
 github.com/inconshreveable/mousetrap v1.1.0/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
@@ -25,7 +26,6 @@ github.com/vishvananda/netns v0.0.5/go.mod h1:SpkAiCQRtJ6TvvxPnOSyH3BMl6unz3xZla
 go.yaml.in/yaml/v3 v3.0.4/go.mod h1:DhzuOOF2ATzADvBadXxruRBLzYTpT36CKvDb3+aBEFg=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/net v0.0.0-20190503192946-f4e77d36d62c/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
-golang.org/x/net v0.0.0-20190603091049-60506f45cf65 h1:+rhAzEzT3f4JtomfC371qB+0Ola2caSKcY69NUBZrRQ=
 golang.org/x/net v0.0.0-20190603091049-60506f45cf65/go.mod h1:HSz+uSET+XFnRR8LxR5pz3Of3rY3CfYBVs4xY44aLks=
 golang.org/x/net v0.47.0 h1:Mx+4dIFzqraBXUugkia1OOvlD6LemFo1ALMHjrXDOhY=
 golang.org/x/net v0.47.0/go.mod h1:/jNxtkgq5yWUGYkaZGqo27cfGZ1c5Nen03aYrrKpVRU=
@@ -35,12 +35,12 @@ golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5h
 golang.org/x/sys v0.0.0-20210927094055-39ccf1dd6fa6/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220209214540-3681064d5158/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.2.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.10.0 h1:SqMFp9UcQJZa+pmYuAKjd9xq1f0j5rLcDIk0mj4qAsA=
 golang.org/x/sys v0.10.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.38.0 h1:3yZWxaJjBmCWXqhN1qh02AkOnCQ1poK6oF+a7xWL6Gc=
 golang.org/x/sys v0.38.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/internal/cmd/test.go b/internal/cmd/test.go
index 0aecdba..e8f3a92 100644
--- a/internal/cmd/test.go
+++ b/internal/cmd/test.go
@@ -367,7 +367,7 @@ func (t *EnvironmentTest) TestCloudEnvironment() {
 		if err == nil {
 			cloudDetected = true
 			t.AddResult("云环境", !test.isFatal, fmt.Sprintf("检测到%s环境", test.name), test.isFatal)
-			t.log.Warn(test.solution)
+			t.log.Warn("%s", test.solution)
 		}
 	}
 
diff --git a/internal/health/factory.go b/internal/health/factory.go
index d7b69ac..c6177c3 100644
--- a/internal/health/factory.go
+++ b/internal/health/factory.go
@@ -8,9 +8,13 @@ import (
 )
 
 func CreateChecker(cfg *config.HealthChecker) (Checker, error) {
+	if cfg.Config == nil {
+		return nil, fmt.Errorf("missing config for checker %s", cfg.Name)
+	}
+
 	configMap, ok := cfg.Config.(map[string]interface{})
 	if !ok {
-		return nil, fmt.Errorf("invalid config for checker %s", cfg.Name)
+		return nil, fmt.Errorf("invalid config type for checker %s: expected map[string]interface{}", cfg.Name)
 	}
 
 	switch cfg.Type {
@@ -36,6 +40,7 @@ func LoadFromConfig(cfg *config.Config, log *logger.Logger) (*Manager, error) {
 			return nil, fmt.Errorf("failed to create checker %s: %w", healthCfg.Name, err)
 		}
 
+		configMap, _ := healthCfg.Config.(map[string]interface{})
 		monitorCfg := &CheckerConfig{
 			Name:     healthCfg.Name,
 			Type:     healthCfg.Type,
@@ -43,7 +48,7 @@ func LoadFromConfig(cfg *config.Config, log *logger.Logger) (*Manager, error) {
 			Timeout:  healthCfg.Timeout,
 			Rise:     healthCfg.Rise,
 			Fall:     healthCfg.Fall,
-			Config:   healthCfg.Config.(map[string]interface{}),
+			Config:   configMap,
 		}
 
 		monitor := NewMonitor(checker, monitorCfg, log)
diff --git a/internal/health/manager.go b/internal/health/manager.go
new file mode 100644
index 0000000..be32cb4
--- /dev/null
+++ b/internal/health/manager.go
@@ -0,0 +1,74 @@
+package health
+
+import (
+	"sync"
+
+	"github.com/loveuer/go-alived/pkg/logger"
+)
+
+// Manager manages multiple health check monitors.
+type Manager struct {
+	monitors map[string]*Monitor
+	mu       sync.RWMutex
+	log      *logger.Logger
+}
+
+// NewManager creates a new health check Manager.
+func NewManager(log *logger.Logger) *Manager {
+	return &Manager{
+		monitors: make(map[string]*Monitor),
+		log:      log,
+	}
+}
+
+// AddMonitor adds a monitor to the manager.
+func (m *Manager) AddMonitor(monitor *Monitor) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.monitors[monitor.config.Name] = monitor
+}
+
+// GetMonitor retrieves a monitor by name.
+func (m *Manager) GetMonitor(name string) (*Monitor, bool) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	monitor, ok := m.monitors[name]
+	return monitor, ok
+}
+
+// StartAll starts all registered monitors.
+func (m *Manager) StartAll() {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	for _, monitor := range m.monitors {
+		monitor.Start()
+	}
+
+	m.log.Info("started %d health check monitor(s)", len(m.monitors))
+}
+
+// StopAll stops all registered monitors.
+func (m *Manager) StopAll() {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	for _, monitor := range m.monitors {
+		monitor.Stop()
+	}
+
+	m.log.Info("stopped all health check monitors")
+}
+
+// GetAllStates returns the current state of all monitors.
+func (m *Manager) GetAllStates() map[string]*CheckerState {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	states := make(map[string]*CheckerState)
+	for name, monitor := range m.monitors {
+		states[name] = monitor.GetState()
+	}
+
+	return states
+}
diff --git a/internal/health/monitor.go b/internal/health/monitor.go
index 331ddca..ff4f857 100644
--- a/internal/health/monitor.go
+++ b/internal/health/monitor.go
@@ -8,6 +8,7 @@ import (
 	"github.com/loveuer/go-alived/pkg/logger"
 )
 
+// Monitor runs periodic health checks and tracks state.
 type Monitor struct {
 	checker   Checker
 	config    *CheckerConfig
@@ -21,6 +22,7 @@ type Monitor struct {
 	mu      sync.RWMutex
 }
 
+// NewMonitor creates a new Monitor for the given checker.
 func NewMonitor(checker Checker, config *CheckerConfig, log *logger.Logger) *Monitor {
 	return &Monitor{
 		checker: checker,
@@ -35,6 +37,7 @@ func NewMonitor(checker Checker, config *CheckerConfig, log *logger.Logger) *Mon
 	}
 }
 
+// Start begins the health check loop.
 func (m *Monitor) Start() {
 	m.mu.Lock()
 	if m.running {
@@ -51,6 +54,7 @@ func (m *Monitor) Start() {
 	go m.checkLoop()
 }
 
+// Stop stops the health check loop.
 func (m *Monitor) Stop() {
 	m.mu.Lock()
 	if !m.running {
@@ -71,6 +75,7 @@ func (m *Monitor) checkLoop() {
 	ticker := time.NewTicker(m.config.Interval)
 	defer ticker.Stop()
 
+	// Perform initial check immediately
 	m.performCheck()
 
 	for {
@@ -95,7 +100,8 @@ func (m *Monitor) performCheck() {
 	oldHealthy := m.state.Healthy
 	stateChanged := m.state.Update(result, m.config.Rise, m.config.Fall)
 	newHealthy := m.state.Healthy
-	callbacks := m.callbacks
+	callbacks := make([]StateChangeCallback, len(m.callbacks))
+	copy(callbacks, m.callbacks)
 	m.mu.Unlock()
 
 	m.log.Debug("[HealthCheck:%s] check completed: result=%s, duration=%s, healthy=%v",
@@ -111,12 +117,14 @@ func (m *Monitor) performCheck() {
 	}
 }
 
+// OnStateChange registers a callback for health state changes.
 func (m *Monitor) OnStateChange(callback StateChangeCallback) {
 	m.mu.Lock()
 	defer m.mu.Unlock()
 	m.callbacks = append(m.callbacks, callback)
 }
 
+// GetState returns a copy of the current checker state.
 func (m *Monitor) GetState() *CheckerState {
 	m.mu.RLock()
 	defer m.mu.RUnlock()
@@ -125,68 +133,9 @@ func (m *Monitor) GetState() *CheckerState {
 	return &stateCopy
 }
 
+// IsHealthy returns whether the checker is currently healthy.
 func (m *Monitor) IsHealthy() bool {
 	m.mu.RLock()
 	defer m.mu.RUnlock()
 	return m.state.Healthy
 }
-
-type Manager struct {
-	monitors map[string]*Monitor
-	mu       sync.RWMutex
-	log      *logger.Logger
-}
-
-func NewManager(log *logger.Logger) *Manager {
-	return &Manager{
-		monitors: make(map[string]*Monitor),
-		log:      log,
-	}
-}
-
-func (m *Manager) AddMonitor(monitor *Monitor) {
-	m.mu.Lock()
-	defer m.mu.Unlock()
-	m.monitors[monitor.config.Name] = monitor
-}
-
-func (m *Manager) GetMonitor(name string) (*Monitor, bool) {
-	m.mu.RLock()
-	defer m.mu.RUnlock()
-	monitor, ok := m.monitors[name]
-	return monitor, ok
-}
-
-func (m *Manager) StartAll() {
-	m.mu.RLock()
-	defer m.mu.RUnlock()
-
-	for _, monitor := range m.monitors {
-		monitor.Start()
-	}
-
-	m.log.Info("started %d health check monitor(s)", len(m.monitors))
-}
-
-func (m *Manager) StopAll() {
-	m.mu.RLock()
-	defer m.mu.RUnlock()
-
-	for _, monitor := range m.monitors {
-		monitor.Stop()
-	}
-
-	m.log.Info("stopped all health check monitors")
-}
-
-func (m *Manager) GetAllStates() map[string]*CheckerState {
-	m.mu.RLock()
-	defer m.mu.RUnlock()
-
-	states := make(map[string]*CheckerState)
-	for name, monitor := range m.monitors {
-		states[name] = monitor.GetState()
-	}
-
-	return states
-}
diff --git a/internal/vrrp/history.go b/internal/vrrp/history.go
new file mode 100644
index 0000000..2b81545
--- /dev/null
+++ b/internal/vrrp/history.go
@@ -0,0 +1,95 @@
+package vrrp
+
+import (
+	"fmt"
+	"sync"
+	"time"
+)
+
+// StateTransition represents a single state transition event.
+type StateTransition struct {
+	From      State
+	To        State
+	Timestamp time.Time
+	Reason    string
+}
+
+// StateHistory maintains a bounded history of state transitions.
+type StateHistory struct {
+	transitions []StateTransition
+	maxSize     int
+	mu          sync.RWMutex
+}
+
+// NewStateHistory creates a new StateHistory with the specified maximum size.
+func NewStateHistory(maxSize int) *StateHistory {
+	return &StateHistory{
+		transitions: make([]StateTransition, 0, maxSize),
+		maxSize:     maxSize,
+	}
+}
+
+// Add records a new state transition.
+func (sh *StateHistory) Add(from, to State, reason string) {
+	sh.mu.Lock()
+	defer sh.mu.Unlock()
+
+	transition := StateTransition{
+		From:      from,
+		To:        to,
+		Timestamp: time.Now(),
+		Reason:    reason,
+	}
+
+	sh.transitions = append(sh.transitions, transition)
+
+	// Maintain bounded size using ring buffer style
+	if len(sh.transitions) > sh.maxSize {
+		// Copy to new slice to allow garbage collection of old backing array
+		newTransitions := make([]StateTransition, len(sh.transitions)-1, sh.maxSize)
+		copy(newTransitions, sh.transitions[1:])
+		sh.transitions = newTransitions
+	}
+}
+
+// GetRecent returns the most recent n transitions.
+func (sh *StateHistory) GetRecent(n int) []StateTransition {
+	sh.mu.RLock()
+	defer sh.mu.RUnlock()
+
+	if n > len(sh.transitions) {
+		n = len(sh.transitions)
+	}
+
+	start := len(sh.transitions) - n
+	result := make([]StateTransition, n)
+	copy(result, sh.transitions[start:])
+
+	return result
+}
+
+// Len returns the number of recorded transitions.
+func (sh *StateHistory) Len() int {
+	sh.mu.RLock()
+	defer sh.mu.RUnlock()
+	return len(sh.transitions)
+}
+
+// String returns a formatted string representation of the history.
+func (sh *StateHistory) String() string {
+	sh.mu.RLock()
+	defer sh.mu.RUnlock()
+
+	if len(sh.transitions) == 0 {
+		return "No state transitions"
+	}
+
+	result := "State transition history:\n"
+	for _, t := range sh.transitions {
+		result += fmt.Sprintf("  %s: %s -> %s (%s)\n",
+			t.Timestamp.Format("2006-01-02 15:04:05"),
+			t.From, t.To, t.Reason)
+	}
+
+	return result
+}
diff --git a/internal/vrrp/instance.go b/internal/vrrp/instance.go
index eb90a4f..3202406 100644
--- a/internal/vrrp/instance.go
+++ b/internal/vrrp/instance.go
@@ -17,6 +17,7 @@ type Instance struct {
 	AdvertInterval  uint8
 	Interface       string
 	VirtualIPs      []net.IP
+	VirtualIPCIDRs  []string // preserve original CIDR notation
 	AuthType        uint8
 	AuthPass        string
 	TrackScripts    []string
@@ -64,12 +65,14 @@ func NewInstance(
 	}
 
 	virtualIPs := make([]net.IP, 0, len(vips))
+	virtualIPCIDRs := make([]string, 0, len(vips))
 	for _, vip := range vips {
 		ip, _, err := net.ParseCIDR(vip)
 		if err != nil {
 			return nil, fmt.Errorf("invalid VIP %s: %w", vip, err)
 		}
 		virtualIPs = append(virtualIPs, ip)
+		virtualIPCIDRs = append(virtualIPCIDRs, vip)
 	}
 
 	var authTypeNum uint8
@@ -94,6 +97,7 @@ func NewInstance(
 		AdvertInterval:  advertInt,
 		Interface:       iface,
 		VirtualIPs:      virtualIPs,
+		VirtualIPCIDRs:  virtualIPCIDRs,
 		AuthType:        authTypeNum,
 		AuthPass:        authPass,
 		TrackScripts:    trackScripts,
@@ -192,8 +196,15 @@ func (inst *Instance) receiveLoop() {
 		default:
 		}
 
+		// Set read deadline to allow periodic check of stop channel
+		inst.socket.SetReadDeadline(time.Now().Add(100 * time.Millisecond))
+
 		pkt, srcIP, err := inst.socket.Receive()
 		if err != nil {
+			// Check if it's a timeout error, which is expected
+			if netErr, ok := err.(interface{ Timeout() bool }); ok && netErr.Timeout() {
+				continue
+			}
 			inst.log.Debug("[%s] failed to receive packet: %v", inst.Name, err)
 			continue
 		}
@@ -371,11 +382,7 @@ func (inst *Instance) removeVIPs() error {
 }
 
 func (inst *Instance) getVIPsWithCIDR() []string {
-	result := make([]string, len(inst.VirtualIPs))
-	for i, ip := range inst.VirtualIPs {
-		result[i] = ip.String() + "/32"
-	}
-	return result
+	return inst.VirtualIPCIDRs
 }
 
 func (inst *Instance) GetState() State {
@@ -399,15 +406,17 @@ func (inst *Instance) AdjustPriority(delta int) {
 	defer inst.mu.Unlock()
 
 	oldPriority := inst.priorityCalc.GetPriority()
-	
+
 	if delta < 0 {
 		inst.priorityCalc.DecreasePriority(uint8(-delta))
+	} else if delta > 0 {
+		inst.priorityCalc.IncreasePriority(uint8(delta))
 	}
-	
+
 	newPriority := inst.priorityCalc.GetPriority()
-	
+
 	if oldPriority != newPriority {
-		inst.log.Info("[%s] priority adjusted: %d -> %d (delta=%d)", 
+		inst.log.Info("[%s] priority adjusted: %d -> %d (delta=%d)",
 			inst.Name, oldPriority, newPriority, delta)
 	}
 }
diff --git a/internal/vrrp/priority.go b/internal/vrrp/priority.go
new file mode 100644
index 0000000..368bf05
--- /dev/null
+++ b/internal/vrrp/priority.go
@@ -0,0 +1,99 @@
+package vrrp
+
+import (
+	"sync"
+	"time"
+)
+
+// PriorityCalculator manages VRRP priority with support for dynamic adjustment.
+type PriorityCalculator struct {
+	basePriority    uint8
+	currentPriority uint8
+	mu              sync.RWMutex
+}
+
+// NewPriorityCalculator creates a new PriorityCalculator with the specified base priority.
+func NewPriorityCalculator(basePriority uint8) *PriorityCalculator {
+	return &PriorityCalculator{
+		basePriority:    basePriority,
+		currentPriority: basePriority,
+	}
+}
+
+// GetPriority returns the current priority.
+func (pc *PriorityCalculator) GetPriority() uint8 {
+	pc.mu.RLock()
+	defer pc.mu.RUnlock()
+	return pc.currentPriority
+}
+
+// DecreasePriority decreases the current priority by the specified amount.
+// The priority will not go below 0.
+func (pc *PriorityCalculator) DecreasePriority(amount uint8) {
+	pc.mu.Lock()
+	defer pc.mu.Unlock()
+
+	if pc.currentPriority > amount {
+		pc.currentPriority -= amount
+	} else {
+		pc.currentPriority = 0
+	}
+}
+
+// IncreasePriority increases the current priority by the specified amount.
+// The priority will not exceed 255 or the base priority.
+func (pc *PriorityCalculator) IncreasePriority(amount uint8) {
+	pc.mu.Lock()
+	defer pc.mu.Unlock()
+
+	newPriority := pc.currentPriority + amount
+	if newPriority > pc.basePriority {
+		newPriority = pc.basePriority
+	}
+	if newPriority < pc.currentPriority { // overflow check
+		newPriority = pc.basePriority
+	}
+	pc.currentPriority = newPriority
+}
+
+// ResetPriority resets the priority to the base value.
+func (pc *PriorityCalculator) ResetPriority() {
+	pc.mu.Lock()
+	defer pc.mu.Unlock()
+	pc.currentPriority = pc.basePriority
+}
+
+// SetBasePriority sets a new base priority and resets current priority to match.
+func (pc *PriorityCalculator) SetBasePriority(priority uint8) {
+	pc.mu.Lock()
+	defer pc.mu.Unlock()
+	pc.basePriority = priority
+	pc.currentPriority = priority
+}
+
+// ShouldBecomeMaster determines if the local node should become master
+// based on priority comparison and IP address tie-breaking.
+func ShouldBecomeMaster(localPriority, remotePriority uint8, localIP, remoteIP string) bool {
+	if localPriority > remotePriority {
+		return true
+	}
+
+	if localPriority == remotePriority {
+		return localIP > remoteIP
+	}
+
+	return false
+}
+
+// CalculateMasterDownInterval calculates the master down interval
+// according to VRRP specification: (3 * Advertisement_Interval).
+func CalculateMasterDownInterval(advertInt uint8) time.Duration {
+	return time.Duration(3*int(advertInt)) * time.Second
+}
+
+// CalculateSkewTime calculates the skew time for master down timer
+// according to VRRP specification: ((256 - Priority) / 256).
+func CalculateSkewTime(priority uint8) time.Duration {
+	skew := float64(256-int(priority)) / 256.0
+	return time.Duration(skew * float64(time.Second))
+}
diff --git a/internal/vrrp/socket.go b/internal/vrrp/socket.go
index 39b1937..b1d9dd7 100644
--- a/internal/vrrp/socket.go
+++ b/internal/vrrp/socket.go
@@ -5,6 +5,7 @@ import (
 	"net"
 	"os"
 	"syscall"
+	"time"
 
 	"golang.org/x/net/ipv4"
 )
@@ -14,10 +15,11 @@ const (
 )
 
 type Socket struct {
-	conn     *ipv4.RawConn
-	iface    *net.Interface
-	localIP  net.IP
-	groupIP  net.IP
+	conn       *ipv4.RawConn
+	packetConn net.PacketConn
+	iface      *net.Interface
+	localIP    net.IP
+	groupIP    net.IP
 }
 
 func NewSocket(ifaceName string) (*Socket, error) {
@@ -56,9 +58,8 @@ func NewSocket(ifaceName string) (*Socket, error) {
 	}
 
 	file := os.NewFile(uintptr(fd), "vrrp-socket")
-	defer file.Close()
-
 	packetConn, err := net.FilePacketConn(file)
+	file.Close()
 	if err != nil {
 		return nil, fmt.Errorf("failed to create packet connection: %w", err)
 	}
@@ -86,10 +87,11 @@ func NewSocket(ifaceName string) (*Socket, error) {
 	}
 
 	return &Socket{
-		conn:    rawConn,
-		iface:   iface,
-		localIP: localIP,
-		groupIP: groupIP,
+		conn:       rawConn,
+		packetConn: packetConn,
+		iface:      iface,
+		localIP:    localIP,
+		groupIP:    groupIP,
 	}, nil
 }
 
@@ -133,6 +135,10 @@ func (s *Socket) Receive() (*VRRPPacket, net.IP, error) {
 	return pkt, header.Src, nil
 }
 
+func (s *Socket) SetReadDeadline(t time.Time) error {
+	return s.packetConn.SetReadDeadline(t)
+}
+
 func (s *Socket) Close() error {
 	if err := s.conn.LeaveGroup(s.iface, &net.IPAddr{IP: s.groupIP}); err != nil {
 		return err
diff --git a/internal/vrrp/state.go b/internal/vrrp/state.go
index efec825..ad1f1ba 100644
--- a/internal/vrrp/state.go
+++ b/internal/vrrp/state.go
@@ -1,11 +1,8 @@
 package vrrp
 
-import (
-	"fmt"
-	"sync"
-	"time"
-)
+import "sync"
 
+// State represents the VRRP instance state.
 type State int
 
 const (
@@ -15,6 +12,7 @@ const (
 	StateFault
 )
 
+// String returns the string representation of the state.
 func (s State) String() string {
 	switch s {
 	case StateInit:
@@ -30,33 +28,39 @@ func (s State) String() string {
 	}
 }
 
+// StateMachine manages VRRP state transitions with thread-safe callbacks.
 type StateMachine struct {
-	currentState     State
-	previousState    State
-	mu               sync.RWMutex
+	currentState         State
+	mu                   sync.RWMutex
 	stateChangeCallbacks []func(old, new State)
 }
 
+// NewStateMachine creates a new StateMachine with the specified initial state.
 func NewStateMachine(initialState State) *StateMachine {
 	return &StateMachine{
-		currentState:  initialState,
-		previousState: StateInit,
+		currentState:         initialState,
 		stateChangeCallbacks: make([]func(old, new State), 0),
 	}
 }
 
+// GetState returns the current state.
 func (sm *StateMachine) GetState() State {
 	sm.mu.RLock()
 	defer sm.mu.RUnlock()
 	return sm.currentState
 }
 
+// SetState transitions to a new state and triggers registered callbacks.
 func (sm *StateMachine) SetState(newState State) {
 	sm.mu.Lock()
 	oldState := sm.currentState
-	sm.previousState = oldState
+	if oldState == newState {
+		sm.mu.Unlock()
+		return
+	}
 	sm.currentState = newState
-	callbacks := sm.stateChangeCallbacks
+	callbacks := make([]func(old, new State), len(sm.stateChangeCallbacks))
+	copy(callbacks, sm.stateChangeCallbacks)
 	sm.mu.Unlock()
 
 	for _, callback := range callbacks {
@@ -64,195 +68,9 @@ func (sm *StateMachine) SetState(newState State) {
 	}
 }
 
+// OnStateChange registers a callback to be invoked on state changes.
 func (sm *StateMachine) OnStateChange(callback func(old, new State)) {
 	sm.mu.Lock()
 	defer sm.mu.Unlock()
 	sm.stateChangeCallbacks = append(sm.stateChangeCallbacks, callback)
 }
-
-type Timer struct {
-	duration time.Duration
-	timer    *time.Timer
-	callback func()
-	mu       sync.Mutex
-}
-
-func NewTimer(duration time.Duration, callback func()) *Timer {
-	return &Timer{
-		duration: duration,
-		callback: callback,
-	}
-}
-
-func (t *Timer) Start() {
-	t.mu.Lock()
-	defer t.mu.Unlock()
-
-	if t.timer != nil {
-		t.timer.Stop()
-	}
-
-	t.timer = time.AfterFunc(t.duration, t.callback)
-}
-
-func (t *Timer) Stop() {
-	t.mu.Lock()
-	defer t.mu.Unlock()
-
-	if t.timer != nil {
-		t.timer.Stop()
-		t.timer = nil
-	}
-}
-
-func (t *Timer) Reset() {
-	t.mu.Lock()
-	defer t.mu.Unlock()
-
-	if t.timer != nil {
-		t.timer.Stop()
-	}
-
-	t.timer = time.AfterFunc(t.duration, t.callback)
-}
-
-func (t *Timer) SetDuration(duration time.Duration) {
-	t.mu.Lock()
-	defer t.mu.Unlock()
-	t.duration = duration
-}
-
-type PriorityCalculator struct {
-	basePriority    uint8
-	currentPriority uint8
-	mu              sync.RWMutex
-}
-
-func NewPriorityCalculator(basePriority uint8) *PriorityCalculator {
-	return &PriorityCalculator{
-		basePriority:    basePriority,
-		currentPriority: basePriority,
-	}
-}
-
-func (pc *PriorityCalculator) GetPriority() uint8 {
-	pc.mu.RLock()
-	defer pc.mu.RUnlock()
-	return pc.currentPriority
-}
-
-func (pc *PriorityCalculator) DecreasePriority(amount uint8) {
-	pc.mu.Lock()
-	defer pc.mu.Unlock()
-
-	if pc.currentPriority > amount {
-		pc.currentPriority -= amount
-	} else {
-		pc.currentPriority = 0
-	}
-}
-
-func (pc *PriorityCalculator) ResetPriority() {
-	pc.mu.Lock()
-	defer pc.mu.Unlock()
-	pc.currentPriority = pc.basePriority
-}
-
-func (pc *PriorityCalculator) SetBasePriority(priority uint8) {
-	pc.mu.Lock()
-	defer pc.mu.Unlock()
-	pc.basePriority = priority
-	pc.currentPriority = priority
-}
-
-func ShouldBecomeMaster(localPriority, remotePriority uint8, localIP, remoteIP string) bool {
-	if localPriority > remotePriority {
-		return true
-	}
-
-	if localPriority == remotePriority {
-		return localIP > remoteIP
-	}
-
-	return false
-}
-
-func CalculateMasterDownInterval(advertInt uint8) time.Duration {
-	return time.Duration(3*int(advertInt)) * time.Second
-}
-
-func CalculateSkewTime(priority uint8) time.Duration {
-	skew := float64(256-int(priority)) / 256.0
-	return time.Duration(skew * float64(time.Second))
-}
-
-type StateTransition struct {
-	From      State
-	To        State
-	Timestamp time.Time
-	Reason    string
-}
-
-type StateHistory struct {
-	transitions []StateTransition
-	maxSize     int
-	mu          sync.RWMutex
-}
-
-func NewStateHistory(maxSize int) *StateHistory {
-	return &StateHistory{
-		transitions: make([]StateTransition, 0, maxSize),
-		maxSize:     maxSize,
-	}
-}
-
-func (sh *StateHistory) Add(from, to State, reason string) {
-	sh.mu.Lock()
-	defer sh.mu.Unlock()
-
-	transition := StateTransition{
-		From:      from,
-		To:        to,
-		Timestamp: time.Now(),
-		Reason:    reason,
-	}
-
-	sh.transitions = append(sh.transitions, transition)
-
-	if len(sh.transitions) > sh.maxSize {
-		sh.transitions = sh.transitions[1:]
-	}
-}
-
-func (sh *StateHistory) GetRecent(n int) []StateTransition {
-	sh.mu.RLock()
-	defer sh.mu.RUnlock()
-
-	if n > len(sh.transitions) {
-		n = len(sh.transitions)
-	}
-
-	start := len(sh.transitions) - n
-	result := make([]StateTransition, n)
-	copy(result, sh.transitions[start:])
-
-	return result
-}
-
-func (sh *StateHistory) String() string {
-	sh.mu.RLock()
-	defer sh.mu.RUnlock()
-
-	if len(sh.transitions) == 0 {
-		return "No state transitions"
-	}
-
-	result := "State transition history:\n"
-	for _, t := range sh.transitions {
-		result += fmt.Sprintf("  %s: %s -> %s (%s)\n",
-			t.Timestamp.Format("2006-01-02 15:04:05"),
-			t.From, t.To, t.Reason)
-	}
-
-	return result
-}
\ No newline at end of file
diff --git a/internal/vrrp/timer.go b/internal/vrrp/timer.go
new file mode 100644
index 0000000..3ecef07
--- /dev/null
+++ b/internal/vrrp/timer.go
@@ -0,0 +1,64 @@
+package vrrp
+
+import (
+	"sync"
+	"time"
+)
+
+// Timer provides a thread-safe timer with callback support.
+type Timer struct {
+	duration time.Duration
+	timer    *time.Timer
+	callback func()
+	mu       sync.Mutex
+}
+
+// NewTimer creates a new Timer with the specified duration and callback.
+func NewTimer(duration time.Duration, callback func()) *Timer {
+	return &Timer{
+		duration: duration,
+		callback: callback,
+	}
+}
+
+// Start starts or restarts the timer.
+func (t *Timer) Start() {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	if t.timer != nil {
+		t.timer.Stop()
+	}
+
+	t.timer = time.AfterFunc(t.duration, t.callback)
+}
+
+// Stop stops the timer if it's running.
+func (t *Timer) Stop() {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	if t.timer != nil {
+		t.timer.Stop()
+		t.timer = nil
+	}
+}
+
+// Reset stops the current timer and starts a new one with the same duration.
+func (t *Timer) Reset() {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	if t.timer != nil {
+		t.timer.Stop()
+	}
+
+	t.timer = time.AfterFunc(t.duration, t.callback)
+}
+
+// SetDuration updates the timer's duration for future starts.
+func (t *Timer) SetDuration(duration time.Duration) {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	t.duration = duration
+}