p2p/nat: use IP.IsPrivate

[dbadoy]

// IsPrivate reports whether ip is a private address, according to
// RFC 1918 (IPv4 addresses) and RFC 4193 (IPv6 addresses).
func (ip IP) IsPrivate() bool {
	if ip4 := ip.To4(); ip4 != nil {
		// Following RFC 1918, Section 3. Private Address Space which says:
		//   The Internet Assigned Numbers Authority (IANA) has reserved the
		//   following three blocks of the IP address space for private internets:
		//     10.0.0.0        -   10.255.255.255  (10/8 prefix)
		//     172.16.0.0      -   172.31.255.255  (172.16/12 prefix)
		//     192.168.0.0     -   192.168.255.255 (192.168/16 prefix)
		return ip4[0] == 10 ||
			(ip4[0] == 172 && ip4[1]&0xf0 == 16) ||
			(ip4[0] == 192 && ip4[1] == 168)
	}
	// Following RFC 4193, Section 8. IANA Considerations which says:
	//   The IANA has assigned the FC00::/7 prefix to "Unique Local Unicast".
	return len(ip) == IPv6len && ip[0]&0xfe == 0xfc
}

It's added in Go 1.17.

[holiman]

LGTM.
However, we also have a similar thing here:

go-ethereum/p2p/netutil/net.go

Line 35 in d8ff53d

lan4.Add("10.0.0.0/8") // Private Use

, but this also contains a few more segments for link-local etc.

[holiman]

LGTM.
However, we also have a similar thing here:

go-ethereum/p2p/netutil/net.go

Line 35 in d8ff53d

lan4.Add("10.0.0.0/8") // Private Use

, but this also contains a few more segments for link-local etc.