txthinking/brook · error

Invalid v4 IP

Error message

Invalid v4 IP

What it means

Constructor validation in NewDHCPServer: at least one of the serverip, start, mask, or gateway arguments failed net.ParseIP(...).To4() (nil), i.e. it is empty, malformed, or an IPv6 address, and a DHCPv4 server cannot be built from it. The generic guard does not say which argument is at fault, so all four must be checked.

Solutions

1. Check each argument (serverip, start, mask, gateway) is a valid dotted-quad IPv4 address
2. Ensure no argument is empty or an IPv6 address

When it happens

Trigger: Thrown at dhcpserver.go:40 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of txthinking/brook@5cd13ef3b1 (2026-09-06). Data as JSON: /api/errors/1b04d90783c3a077. Report an issue: GitHub.

Appendix: source

Thrown at dhcpserver.go:40

	"path/filepath"
	"time"

	"github.com/krolaw/dhcp4"
)

type DHCPServer struct {
	Listen   net.PacketConn
	ServerIP net.IP
	Start    net.IP
	Count    int
	Leases   map[int]string
	Options  dhcp4.Options
	Cache    string
}

func NewDHCPServer(iface, serverip, start, mask string, count int, gateway string, dnsserver []string, cache string) (*DHCPServer, error) {
	if net.ParseIP(serverip).To4() == nil || net.ParseIP(start).To4() == nil || net.ParseIP(mask).To4() == nil || net.ParseIP(gateway).To4() == nil {
		return nil, errors.New("Invalid v4 IP")
	}
	dnsserverips := make([]net.IP, 0)
	for _, v := range dnsserver {
		if net.ParseIP(v).To4() == nil {
			return nil, errors.New("Invalid v4 IP")
		}
		dnsserverips = append(dnsserverips, net.ParseIP(v).To4())
	}
	if cache == "" {
		s, err := os.UserHomeDir()
		if err != nil {
			return nil, err
		}
		cache = filepath.Join(s, ".brook.dhcpserver")
	}
	b, err := os.ReadFile(cache)
	if err != nil && !os.IsNotExist(err) {
		return nil, err

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