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.

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

View on GitHub (pinned to 5cd13ef3b1)

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.