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dns: IPv6 roots generation

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This commit is contained in:
Csaba Sarkadi 2022-01-15 16:18:49 +01:00
parent 1a6e5d8770
commit 115d0cbe85
2 changed files with 105 additions and 10 deletions
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69
dns.go
View File

@ -14,6 +14,11 @@ const (
ByteSize = 8
)
const (
ipv4AddressLength = 32
ipv6AddressLength = 128
)
// generateMagicDNSRootDomains generates a list of DNS entries to be included in `Routes` in `MapResponse`.
// This list of reverse DNS entries instructs the OS on what subnets and domains the Tailscale embedded DNS
// server (listening in 100.100.100.100 udp/53) should be used for.
@ -37,22 +42,25 @@ const (
func generateMagicDNSRootDomains(ipPrefixes []netaddr.IPPrefix) []dnsname.FQDN {
fqdns := make([]dnsname.FQDN, 0, len(ipPrefixes))
for _, ipPrefix := range ipPrefixes {
var generateDnsRoot func(netaddr.IPPrefix) []dnsname.FQDN
var generateDNSRoot func(netaddr.IPPrefix) []dnsname.FQDN
switch ipPrefix.IP().BitLen() {
case 32:
generateDnsRoot = generateIPv4DNSRootDomain
case ipv4AddressLength:
generateDNSRoot = generateIPv4DNSRootDomain
case ipv6AddressLength:
generateDNSRoot = generateIPv6DNSRootDomain
default:
panic(fmt.Sprintf("unsupported IP version with address length %d", ipPrefix.IP().BitLen()))
}
fqdns = append(fqdns, generateDnsRoot(ipPrefix)...)
fqdns = append(fqdns, generateDNSRoot(ipPrefix)...)
}
return fqdns
}
func generateIPv4DNSRootDomain(ipPrefix netaddr.IPPrefix) (fqdns []dnsname.FQDN) {
func generateIPv4DNSRootDomain(ipPrefix netaddr.IPPrefix) []dnsname.FQDN {
// Conversion to the std lib net.IPnet, a bit easier to operate
netRange := ipPrefix.IPNet()
maskBits, _ := netRange.Mask.Size()
@ -76,6 +84,7 @@ func generateIPv4DNSRootDomain(ipPrefix netaddr.IPPrefix) (fqdns []dnsname.FQDN)
rdnsSlice = append(rdnsSlice, "in-addr.arpa.")
rdnsBase := strings.Join(rdnsSlice, ".")
fqdns := make([]dnsname.FQDN, 0, max-min+1)
for i := min; i <= max; i++ {
fqdn, err := dnsname.ToFQDN(fmt.Sprintf("%d.%s", i, rdnsBase))
if err != nil {
@ -84,7 +93,55 @@ func generateIPv4DNSRootDomain(ipPrefix netaddr.IPPrefix) (fqdns []dnsname.FQDN)
fqdns = append(fqdns, fqdn)
}
return
return fqdns
}
func generateIPv6DNSRootDomain(ipPrefix netaddr.IPPrefix) []dnsname.FQDN {
const nibbleLen = 4
maskBits, _ := ipPrefix.IPNet().Mask.Size()
expanded := ipPrefix.IP().StringExpanded()
nibbleStr := strings.Map(func(r rune) rune {
if r == ':' {
return -1
}
return r
}, expanded)
// TODO?: that does not look the most efficient implementation,
// but the inputs are not so long as to cause problems,
// and from what I can see, the generateMagicDNSRootDomains
// function is called only once over the lifetime of a server process.
prefixConstantParts := []string{}
for i := 0; i < maskBits/nibbleLen; i++ {
prefixConstantParts = append([]string{string(nibbleStr[i])}, prefixConstantParts...)
}
makeDomain := func(variablePrefix ...string) (dnsname.FQDN, error) {
prefix := strings.Join(append(variablePrefix, prefixConstantParts...), ".")
return dnsname.ToFQDN(fmt.Sprintf("%s.ip6.arpa", prefix))
}
var fqdns []dnsname.FQDN
if maskBits%4 == 0 {
dom, _ := makeDomain()
fqdns = append(fqdns, dom)
} else {
domCount := 1 << (maskBits % nibbleLen)
fqdns = make([]dnsname.FQDN, 0, domCount)
for i := 0; i < domCount; i++ {
varNibble := fmt.Sprintf("%x", i)
dom, err := makeDomain(varNibble)
if err != nil {
continue
}
fqdns = append(fqdns, dom)
}
}
return fqdns
}
func getMapResponseDNSConfig(

46
dns_test.go
View File

@ -10,8 +10,10 @@ import (
)
func (s *Suite) TestMagicDNSRootDomains100(c *check.C) {
prefix := netaddr.MustParseIPPrefix("100.64.0.0/10")
domains := generateMagicDNSRootDomains(prefix)
prefixes := []netaddr.IPPrefix{
netaddr.MustParseIPPrefix("100.64.0.0/10"),
}
domains := generateMagicDNSRootDomains(prefixes)
found := false
for _, domain := range domains {
@ -45,8 +47,10 @@ func (s *Suite) TestMagicDNSRootDomains100(c *check.C) {
}
func (s *Suite) TestMagicDNSRootDomains172(c *check.C) {
prefix := netaddr.MustParseIPPrefix("172.16.0.0/16")
domains := generateMagicDNSRootDomains(prefix)
prefixes := []netaddr.IPPrefix{
netaddr.MustParseIPPrefix("172.16.0.0/16"),
}
domains := generateMagicDNSRootDomains(prefixes)
found := false
for _, domain := range domains {
@ -69,6 +73,40 @@ func (s *Suite) TestMagicDNSRootDomains172(c *check.C) {
c.Assert(found, check.Equals, true)
}
// Happens when netmask is a multiple of 4 bits (sounds likely).
func (s *Suite) TestMagicDNSRootDomainsIPv6Single(c *check.C) {
prefixes := []netaddr.IPPrefix{
netaddr.MustParseIPPrefix("fd7a:115c:a1e0::/48"),
}
domains := generateMagicDNSRootDomains(prefixes)
c.Assert(len(domains), check.Equals, 1)
c.Assert(domains[0].WithTrailingDot(), check.Equals, "0.e.1.a.c.5.1.1.a.7.d.f.ip6.arpa.")
}
func (s *Suite) TestMagicDNSRootDomainsIPv6SingleMultiple(c *check.C) {
prefixes := []netaddr.IPPrefix{
netaddr.MustParseIPPrefix("fd7a:115c:a1e0::/50"),
}
domains := generateMagicDNSRootDomains(prefixes)
yieldsRoot := func(dom string) bool {
for _, candidate := range domains {
if candidate.WithTrailingDot() == dom {
return true
}
}
return false
}
c.Assert(len(domains), check.Equals, 4)
c.Assert(yieldsRoot("0.0.e.1.a.c.5.1.1.a.7.d.f.ip6.arpa."), check.Equals, true)
c.Assert(yieldsRoot("1.0.e.1.a.c.5.1.1.a.7.d.f.ip6.arpa."), check.Equals, true)
c.Assert(yieldsRoot("2.0.e.1.a.c.5.1.1.a.7.d.f.ip6.arpa."), check.Equals, true)
c.Assert(yieldsRoot("3.0.e.1.a.c.5.1.1.a.7.d.f.ip6.arpa."), check.Equals, true)
}
func (s *Suite) TestDNSConfigMapResponseWithMagicDNS(c *check.C) {
namespaceShared1, err := app.CreateNamespace("shared1")
c.Assert(err, check.IsNil)