Esempio n. 1
0
func RenewDnsMsg(m *dns.Msg) {
	m.Extra = nil
	m.Answer = nil
	m.AuthenticatedData = false
	m.CheckingDisabled = false
	m.Question = nil
}
Esempio n. 2
0
func cacheMsg(m *dns.Msg, tc cacheTestCase) *dns.Msg {
	m.RecursionAvailable = tc.RecursionAvailable
	m.AuthenticatedData = tc.AuthenticatedData
	m.Authoritative = tc.Authoritative
	m.Truncated = tc.Truncated
	m.Answer = tc.in.Answer
	m.Ns = tc.in.Ns
	//	m.Extra = tc.in.Extra , not the OPT record!
	return m
}
Esempio n. 3
0
// toMsg turns i into a message, it tailers to reply to m.
func (i *item) toMsg(m *dns.Msg) *dns.Msg {
	m1 := new(dns.Msg)
	m1.SetReply(m)
	m1.Authoritative = i.Authoritative
	m1.AuthenticatedData = i.AuthenticatedData
	m1.RecursionAvailable = i.RecursionAvailable
	m1.Compress = true

	m1.Answer = i.Answer
	m1.Ns = i.Ns
	m1.Extra = i.Extra

	ttl := int(i.origTtl) - int(time.Now().UTC().Sub(i.stored).Seconds())
	if ttl < baseTtl {
		ttl = baseTtl
	}
	setCap(m1, uint32(ttl))
	return m1
}
Esempio n. 4
0
/*
 * makeMessage() - construct DNS message structure
 */
func makeMessage(c *Context, qname, qtype, qclass string, ext Extension) *dns.Msg {

	m := new(dns.Msg)
	m.Id = dns.Id()

	if c.restype == RESOLUTION_STUB {
		m.RecursionDesired = true
	} else {
		m.RecursionDesired = false
	}

	if c.adflag {
		m.AuthenticatedData = true
	}

	if c.cdflag {
		m.CheckingDisabled = true
	}

	if ext["dnssec_return_status"] || ext["dnssec_return_only_secure"] || ext["dnssec_return_validation_chain"] {
		opt := new(dns.OPT)
		opt.Hdr.Name = "."
		opt.Hdr.Rrtype = dns.TypeOPT
		opt.SetDo()
		m.Extra = append(m.Extra, opt)
	}

	m.Question = make([]dns.Question, 1)
	qtype_int, ok := dns.StringToType[strings.ToUpper(qtype)]
	if !ok {
		fmt.Printf("%s: Unrecognized query type.\n", qtype)
		return nil
	}
	qclass_int, ok := dns.StringToClass[strings.ToUpper(qclass)]
	if !ok {
		fmt.Printf("%s: Unrecognized query class.\n", qclass)
		return nil
	}
	m.Question[0] = dns.Question{qname, qtype_int, qclass_int}

	return m
}
Esempio n. 5
0
// ServeDNS is the handler for DNS requests, responsible for parsing DNS request, possibly forwarding
// it to a real dns server and returning a response.
func (s *server) ServeDNS(w dns.ResponseWriter, req *dns.Msg) {
	m := new(dns.Msg)
	m.SetReply(req)
	m.Authoritative = true
	m.RecursionAvailable = true
	m.Compress = true
	bufsize := uint16(512)
	dnssec := false
	tcp := false
	start := time.Now()

	if req.Question[0].Qtype == dns.TypeANY {
		m.Authoritative = false
		m.Rcode = dns.RcodeRefused
		m.RecursionAvailable = false
		m.RecursionDesired = false
		m.Compress = false
		// if write fails don't care
		w.WriteMsg(m)

		promErrorCount.WithLabelValues("refused").Inc()
		return
	}

	if o := req.IsEdns0(); o != nil {
		bufsize = o.UDPSize()
		dnssec = o.Do()
	}
	if bufsize < 512 {
		bufsize = 512
	}
	// with TCP we can send 64K
	if tcp = isTCP(w); tcp {
		bufsize = dns.MaxMsgSize - 1
		promRequestCount.WithLabelValues("tcp").Inc()
	} else {
		promRequestCount.WithLabelValues("udp").Inc()
	}

	StatsRequestCount.Inc(1)

	if dnssec {
		StatsDnssecOkCount.Inc(1)
		promDnssecOkCount.Inc()
	}

	defer func() {
		promCacheSize.WithLabelValues("response").Set(float64(s.rcache.Size()))
	}()

	// Check cache first.
	key := cache.QuestionKey(req.Question[0], dnssec)
	m1, exp, hit := s.rcache.Search(key)
	if hit {
		// Cache hit! \o/
		if time.Since(exp) < 0 {
			m1.Id = m.Id
			m1.Compress = true
			m1.Truncated = false

			if dnssec {
				// The key for DNS/DNSSEC in cache is different, no
				// need to do Denial/Sign here.
				//if s.config.PubKey != nil {
				//s.Denial(m1) // not needed for cache hits
				//s.Sign(m1, bufsize)
				//}
			}
			if m1.Len() > int(bufsize) && !tcp {
				promErrorCount.WithLabelValues("truncated").Inc()
				m1.Truncated = true
			}
			// Still round-robin even with hits from the cache.
			// Only shuffle A and AAAA records with each other.
			if req.Question[0].Qtype == dns.TypeA || req.Question[0].Qtype == dns.TypeAAAA {
				s.RoundRobin(m1.Answer)
			}

			if err := w.WriteMsg(m1); err != nil {
				log.Printf("skydns: failure to return reply %q", err)
			}
			metricSizeAndDuration(m1, start, tcp)
			return
		}
		// Expired! /o\
		s.rcache.Remove(key)
	}

	q := req.Question[0]
	name := strings.ToLower(q.Name)

	if s.config.Verbose {
		log.Printf("skydns: received DNS Request for %q from %q with type %d", q.Name, w.RemoteAddr(), q.Qtype)
	}

	for zone, ns := range *s.config.stub {
		if strings.HasSuffix(name, zone) {
			resp := s.ServeDNSStubForward(w, req, ns)
			metricSizeAndDuration(resp, start, tcp)
			return
		}
	}

	// If the qname is local.dns.skydns.local. and s.config.Local != "", substitute that name.
	if s.config.Local != "" && name == s.config.localDomain {
		name = s.config.Local
	}

	if q.Qtype == dns.TypePTR && strings.HasSuffix(name, ".in-addr.arpa.") || strings.HasSuffix(name, ".ip6.arpa.") {
		resp := s.ServeDNSReverse(w, req)
		metricSizeAndDuration(resp, start, tcp)
		return
	}

	if q.Qclass != dns.ClassCHAOS && !strings.HasSuffix(name, s.config.Domain) {
		if s.config.Verbose {
			log.Printf("skydns: %q is not sub of %q, forwarding...", name, s.config.Domain)
		}

		resp := s.ServeDNSForward(w, req)
		metricSizeAndDuration(resp, start, tcp)
		return
	}

	promCacheMiss.WithLabelValues("response").Inc()

	defer func() {
		if m.Rcode == dns.RcodeServerFailure {
			if err := w.WriteMsg(m); err != nil {
				log.Printf("skydns: failure to return reply %q", err)
			}
			return
		}
		// Set TTL to the minimum of the RRset and dedup the message, i.e.
		// remove identical RRs.
		m = s.dedup(m)

		minttl := s.config.Ttl
		if len(m.Answer) > 1 {
			for _, r := range m.Answer {
				if r.Header().Ttl < minttl {
					minttl = r.Header().Ttl
				}
			}
			for _, r := range m.Answer {
				r.Header().Ttl = minttl
			}
		}

		if !m.Truncated {
			s.rcache.InsertMessage(cache.QuestionKey(req.Question[0], dnssec), m)
		}

		if dnssec {
			if s.config.PubKey != nil {
				m.AuthenticatedData = true
				s.Denial(m)
				s.Sign(m, bufsize)
			}
		}

		if m.Len() > dns.MaxMsgSize {
			log.Printf("skydns: overflowing maximum message size: %d, dropping additional section", m.Len())
			m.Extra = nil // Drop entire additional section to see if this helps.

			if m.Len() > dns.MaxMsgSize {
				// *Still* too large.
				log.Printf("skydns: still overflowing maximum message size: %d", m.Len())
				promErrorCount.WithLabelValues("overflow").Inc()
				m1 := new(dns.Msg) // Use smaller msg to signal failure.
				m1.SetRcode(m, dns.RcodeServerFailure)
				if err := w.WriteMsg(m1); err != nil {
					log.Printf("skydns: failure to return reply %q", err)
				}
				metricSizeAndDuration(m1, start, tcp)
				return
			}
		}

		if m.Len() > int(bufsize) && !tcp {
			m.Extra = nil // As above, drop entire additional section.
			if m.Len() > int(bufsize) {
				promErrorCount.WithLabelValues("truncated").Inc()
				m.Truncated = true
			}
		}

		if err := w.WriteMsg(m); err != nil {
			log.Printf("skydns: failure to return reply %q %d", err, m.Len())
		}
		metricSizeAndDuration(m, start, tcp)
	}()

	if name == s.config.Domain {
		if q.Qtype == dns.TypeSOA {
			m.Answer = []dns.RR{s.NewSOA()}
			return
		}
		if q.Qtype == dns.TypeDNSKEY {
			if s.config.PubKey != nil {
				m.Answer = []dns.RR{s.config.PubKey}
				return
			}
		}
	}
	if q.Qclass == dns.ClassCHAOS {
		if q.Qtype == dns.TypeTXT {
			switch name {
			case "authors.bind.":
				fallthrough
			case s.config.Domain:
				hdr := dns.RR_Header{Name: q.Name, Rrtype: dns.TypeTXT, Class: dns.ClassCHAOS, Ttl: 0}
				authors := []string{"Erik St. Martin", "Brian Ketelsen", "Miek Gieben", "Michael Crosby"}
				for _, a := range authors {
					m.Answer = append(m.Answer, &dns.TXT{Hdr: hdr, Txt: []string{a}})
				}
				for j := 0; j < len(authors)*(int(dns.Id())%4+1); j++ {
					q := int(dns.Id()) % len(authors)
					p := int(dns.Id()) % len(authors)
					if q == p {
						p = (p + 1) % len(authors)
					}
					m.Answer[q], m.Answer[p] = m.Answer[p], m.Answer[q]
				}
				return
			case "version.bind.":
				fallthrough
			case "version.server.":
				hdr := dns.RR_Header{Name: q.Name, Rrtype: dns.TypeTXT, Class: dns.ClassCHAOS, Ttl: 0}
				m.Answer = []dns.RR{&dns.TXT{Hdr: hdr, Txt: []string{Version}}}
				return
			case "hostname.bind.":
				fallthrough
			case "id.server.":
				// TODO(miek): machine name to return
				hdr := dns.RR_Header{Name: q.Name, Rrtype: dns.TypeTXT, Class: dns.ClassCHAOS, Ttl: 0}
				m.Answer = []dns.RR{&dns.TXT{Hdr: hdr, Txt: []string{"localhost"}}}
				return
			}
		}
		// still here, fail
		m.SetReply(req)
		m.SetRcode(req, dns.RcodeServerFailure)
		return
	}

	switch q.Qtype {
	case dns.TypeNS:
		if name != s.config.Domain {
			log.Printf("skydns: %q unmatch default domain", name)
			break
		}
		// Lookup s.config.DnsDomain
		records, extra, err := s.NSRecords(q, s.config.dnsDomain)
		if err != nil {
			if e, ok := err.(*etcd.EtcdError); ok {
				if e.ErrorCode == 100 {
					s.NameError(m, req)
					return
				}
			}
		}
		m.Answer = append(m.Answer, records...)
		m.Extra = append(m.Extra, extra...)
	case dns.TypeA, dns.TypeAAAA:
		records, err := s.AddressRecords(q, name, nil, bufsize, dnssec, false)
		if err != nil {
			if e, ok := err.(*etcd.EtcdError); ok {
				if e.ErrorCode == 100 {
					s.NameError(m, req)
					return
				}
			}
		}
		m.Answer = append(m.Answer, records...)
	case dns.TypeTXT:
		records, err := s.TXTRecords(q, name)
		if err != nil {
			if e, ok := err.(*etcd.EtcdError); ok {
				if e.ErrorCode == 100 {
					s.NameError(m, req)
					return
				}
			}
		}
		m.Answer = append(m.Answer, records...)
	case dns.TypeCNAME:
		records, err := s.CNAMERecords(q, name)
		if err != nil {
			if e, ok := err.(*etcd.EtcdError); ok {
				if e.ErrorCode == 100 {
					s.NameError(m, req)
					return
				}
			}
		}
		m.Answer = append(m.Answer, records...)
	case dns.TypeMX:
		records, extra, err := s.MXRecords(q, name, bufsize, dnssec)
		if err != nil {
			if e, ok := err.(*etcd.EtcdError); ok {
				if e.ErrorCode == 100 {
					s.NameError(m, req)
					return
				}
			}
		}
		m.Answer = append(m.Answer, records...)
		m.Extra = append(m.Extra, extra...)
	default:
		fallthrough // also catch other types, so that they return NODATA
	case dns.TypeSRV:
		records, extra, err := s.SRVRecords(q, name, bufsize, dnssec)
		if err != nil {
			if e, ok := err.(*etcd.EtcdError); ok {
				if e.ErrorCode == 100 {
					s.NameError(m, req)
					return
				}
			}
			if q.Qtype == dns.TypeSRV { // Otherwise NODATA
				s.ServerFailure(m, req)
				return
			}
		}
		// if we are here again, check the types, because an answer may only
		// be given for SRV. All other types should return NODATA, the
		// NXDOMAIN part is handled in the above code. TODO(miek): yes this
		// can be done in a more elegant manor.
		if q.Qtype == dns.TypeSRV {
			m.Answer = append(m.Answer, records...)
			m.Extra = append(m.Extra, extra...)
		}
	}

	if len(m.Answer) == 0 { // NODATA response
		StatsNoDataCount.Inc(1)
		m.Ns = []dns.RR{s.NewSOA()}
		m.Ns[0].Header().Ttl = s.config.MinTtl
	}
}
Esempio n. 6
0
// ServeDNS is the handler for DNS requests, responsible for parsing DNS request, possibly forwarding
// it to a real dns server and returning a response.
func (s *server) ServeDNS(w dns.ResponseWriter, req *dns.Msg) {
	m := new(dns.Msg)
	m.SetReply(req)
	m.Authoritative = true
	m.RecursionAvailable = true
	m.Compress = true
	bufsize := uint16(512)
	dnssec := false
	tcp := false

	if req.Question[0].Qtype == dns.TypeANY {
		m.Authoritative = false
		m.Rcode = dns.RcodeRefused
		m.RecursionAvailable = false
		m.RecursionDesired = false
		m.Compress = false
		// if write fails don't care
		w.WriteMsg(m)
		return
	}

	if o := req.IsEdns0(); o != nil {
		bufsize = o.UDPSize()
		dnssec = o.Do()
	}
	if bufsize < 512 {
		bufsize = 512
	}
	// with TCP we can send 64K
	if _, ok := w.RemoteAddr().(*net.TCPAddr); ok {
		bufsize = dns.MaxMsgSize - 1
		tcp = true
	}
	// Check cache first.
	key := cache.QuestionKey(req.Question[0], dnssec)
	m1, exp, hit := s.rcache.Search(key)
	if hit {
		// Cache hit! \o/
		if time.Since(exp) < 0 {
			m1.Id = m.Id
			if dnssec {
				StatsDnssecOkCount.Inc(1)
				// The key for DNS/DNSSEC in cache is different, no
				// need to do Denial/Sign here.
				//if s.config.PubKey != nil {
				//s.Denial(m1) // not needed for cache hits
				//s.Sign(m1, bufsize)
				//}
			}
			if m1.Len() > int(bufsize) && !tcp {
				m1.Truncated = true
			}
			// Still round-robin even with hits from the cache.
			if s.config.RoundRobin && (req.Question[0].Qtype == dns.TypeA ||
				req.Question[0].Qtype == dns.TypeAAAA) {
				switch l := len(m1.Answer); l {
				case 2:
					if dns.Id()%2 == 0 {
						m1.Answer[0], m1.Answer[1] = m1.Answer[1], m1.Answer[0]
					}
				default:
					// Do a minimum of l swap, maximum of 4l swaps
					for j := 0; j < l*(int(dns.Id())%4+1); j++ {
						q := int(dns.Id()) % l
						p := int(dns.Id()) % l
						if q == p {
							p = (p + 1) % l
						}
						m1.Answer[q], m1.Answer[p] = m1.Answer[p], m1.Answer[q]
					}
				}

			}
			if err := w.WriteMsg(m1); err != nil {
				s.config.log.Errorf("failure to return reply %q", err)
			}
			return
		}
		// Expired! /o\
		s.rcache.Remove(key)
	}

	q := req.Question[0]
	name := strings.ToLower(q.Name)
	StatsRequestCount.Inc(1)
	if verbose {
		s.config.log.Infof("received DNS Request for %q from %q with type %d", q.Name, w.RemoteAddr(), q.Qtype)
	}
	// If the qname is local.dns.skydns.local. and s.config.Local != "", substitute that name.
	if s.config.Local != "" && name == s.config.localDomain {
		name = s.config.Local
	}

	if q.Qtype == dns.TypePTR && strings.HasSuffix(name, ".in-addr.arpa.") || strings.HasSuffix(name, ".ip6.arpa.") {
		s.ServeDNSReverse(w, req)
		return
	}

	if q.Qclass != dns.ClassCHAOS && !strings.HasSuffix(name, s.config.Domain) {
		s.ServeDNSForward(w, req)
		return
	}

	defer func() {
		if m.Rcode == dns.RcodeServerFailure {
			if err := w.WriteMsg(m); err != nil {
				s.config.log.Errorf("failure to return reply %q", err)
			}
			return
		}
		// Set TTL to the minimum of the RRset.
		minttl := s.config.Ttl
		if len(m.Answer) > 1 {
			for _, r := range m.Answer {
				if r.Header().Ttl < minttl {
					minttl = r.Header().Ttl
				}
			}
			for _, r := range m.Answer {
				r.Header().Ttl = minttl
			}
		}

		s.rcache.InsertMessage(cache.QuestionKey(req.Question[0], dnssec), m)

		if dnssec {
			StatsDnssecOkCount.Inc(1)
			if s.config.PubKey != nil {
				m.AuthenticatedData = true
				s.Denial(m)
				s.Sign(m, bufsize)
			}
		}
		if m.Len() > int(bufsize) && !tcp {
			// TODO(miek): this is a little brain dead, better is to not add
			// RRs in the message in the first place.
			m.Truncated = true
		}
		if err := w.WriteMsg(m); err != nil {
			s.config.log.Errorf("failure to return reply %q", err)
		}
	}()

	if name == s.config.Domain {
		if q.Qtype == dns.TypeSOA {
			m.Answer = []dns.RR{s.NewSOA()}
			return
		}
		if q.Qtype == dns.TypeDNSKEY {
			if s.config.PubKey != nil {
				m.Answer = []dns.RR{s.config.PubKey}
				return
			}
		}
	}
	if q.Qclass == dns.ClassCHAOS {
		if q.Qtype == dns.TypeTXT {
			switch name {
			case "authors.bind.":
				fallthrough
			case s.config.Domain:
				hdr := dns.RR_Header{Name: q.Name, Rrtype: dns.TypeTXT, Class: dns.ClassCHAOS, Ttl: 0}
				authors := []string{"Erik St. Martin", "Brian Ketelsen", "Miek Gieben", "Michael Crosby"}
				for _, a := range authors {
					m.Answer = append(m.Answer, &dns.TXT{Hdr: hdr, Txt: []string{a}})
				}
				for j := 0; j < len(authors)*(int(dns.Id())%4+1); j++ {
					q := int(dns.Id()) % len(authors)
					p := int(dns.Id()) % len(authors)
					if q == p {
						p = (p + 1) % len(authors)
					}
					m.Answer[q], m.Answer[p] = m.Answer[p], m.Answer[q]
				}
				return
			case "version.bind.":
				fallthrough
			case "version.server.":
				hdr := dns.RR_Header{Name: q.Name, Rrtype: dns.TypeTXT, Class: dns.ClassCHAOS, Ttl: 0}
				m.Answer = []dns.RR{&dns.TXT{Hdr: hdr, Txt: []string{Version}}}
				return
			case "hostname.bind.":
				fallthrough
			case "id.server.":
				// TODO(miek): machine name to return
				hdr := dns.RR_Header{Name: q.Name, Rrtype: dns.TypeTXT, Class: dns.ClassCHAOS, Ttl: 0}
				m.Answer = []dns.RR{&dns.TXT{Hdr: hdr, Txt: []string{"localhost"}}}
				return
			}
		}
		// still here, fail
		m.SetReply(req)
		m.SetRcode(req, dns.RcodeServerFailure)
		return
	}

	switch q.Qtype {
	case dns.TypeNS:
		if name != s.config.Domain {
			break
		}
		// Lookup s.config.DnsDomain
		records, extra, err := s.NSRecords(q, s.config.dnsDomain)
		if err != nil {
			if e, ok := err.(*etcd.EtcdError); ok {
				if e.ErrorCode == 100 {
					s.NameError(m, req)
					return
				}
			}
		}
		m.Answer = append(m.Answer, records...)
		m.Extra = append(m.Extra, extra...)
	case dns.TypeA, dns.TypeAAAA:
		records, err := s.AddressRecords(q, name, nil)
		if err != nil {
			if e, ok := err.(*etcd.EtcdError); ok {
				if e.ErrorCode == 100 {
					s.NameError(m, req)
					return
				}
			}
			if err.Error() == "incomplete CNAME chain" {
				// We can not complete the CNAME internally, *iff* there is a
				// external name in the set, take it, and try to resolve it externally.
				if len(records) == 0 {
					s.NameError(m, req)
					return
				}
				target := ""
				for _, r := range records {
					if v, ok := r.(*dns.CNAME); ok {
						if !dns.IsSubDomain(s.config.Domain, v.Target) {
							target = v.Target
							break
						}
					}
				}
				if target == "" {
					s.config.log.Warningf("incomplete CNAME chain for %s", name)
					s.NoDataError(m, req)
					return
				}
				m1, e1 := s.Lookup(target, req.Question[0].Qtype, bufsize, dnssec)
				if e1 != nil {
					s.config.log.Errorf("%q", err)
					s.NoDataError(m, req)
					return
				}
				records = append(records, m1.Answer...)
			}
		}
		m.Answer = append(m.Answer, records...)
	case dns.TypeCNAME:
		records, err := s.CNAMERecords(q, name)
		if err != nil {
			if e, ok := err.(*etcd.EtcdError); ok {
				if e.ErrorCode == 100 {
					s.NameError(m, req)
					return
				}
			}
		}
		m.Answer = append(m.Answer, records...)
	default:
		fallthrough // also catch other types, so that they return NODATA
	case dns.TypeSRV, dns.TypeANY:
		records, extra, err := s.SRVRecords(q, name, bufsize, dnssec)
		if err != nil {
			if e, ok := err.(*etcd.EtcdError); ok {
				if e.ErrorCode == 100 {
					s.NameError(m, req)
					return
				}
			}
		}
		// if we are here again, check the types, because an answer may only
		// be given for SRV or ANY. All other types should return NODATA, the
		// NXDOMAIN part is handled in the above code. TODO(miek): yes this
		// can be done in a more elegant manor.
		if q.Qtype == dns.TypeSRV || q.Qtype == dns.TypeANY {
			m.Answer = append(m.Answer, records...)
			m.Extra = append(m.Extra, extra...)
		}
	}

	if len(m.Answer) == 0 { // NODATA response
		StatsNoDataCount.Inc(1)
		m.Ns = []dns.RR{s.NewSOA()}
		m.Ns[0].Header().Ttl = s.config.MinTtl
	}
}
Esempio n. 7
0
// ServeDNS is the handler for DNS requests, responsible for parsing DNS request, possibly forwarding
// it to a real dns server and returning a response.
func (s *server) ServeDNS(w dns.ResponseWriter, req *dns.Msg) {
	m := new(dns.Msg)
	m.SetReply(req)
	m.Authoritative = true
	m.RecursionAvailable = true
	m.Compress = true
	bufsize := uint16(512)
	dnssec := false
	tcp := false
	start := time.Now()

	q := req.Question[0]
	name := strings.ToLower(q.Name)

	if q.Qtype == dns.TypeANY {
		m.Authoritative = false
		m.Rcode = dns.RcodeRefused
		m.RecursionAvailable = false
		m.RecursionDesired = false
		m.Compress = false
		// if write fails don't care
		w.WriteMsg(m)

		promErrorCount.WithLabelValues("refused").Inc()
		return
	}

	if o := req.IsEdns0(); o != nil {
		bufsize = o.UDPSize()
		dnssec = o.Do()
	}
	if bufsize < 512 {
		bufsize = 512
	}
	// with TCP we can send 64K
	if tcp = isTCP(w); tcp {
		bufsize = dns.MaxMsgSize - 1
		promRequestCount.WithLabelValues("tcp").Inc()
	} else {
		promRequestCount.WithLabelValues("udp").Inc()
	}

	StatsRequestCount.Inc(1)

	if dnssec {
		StatsDnssecOkCount.Inc(1)
		promDnssecOkCount.Inc()
	}

	if s.config.Verbose {
		logf("received DNS Request for %q from %q with type %d", q.Name, w.RemoteAddr(), q.Qtype)
	}

	// Check cache first.
	m1 := s.rcache.Hit(q, dnssec, tcp, m.Id)
	if m1 != nil {
		if tcp {
			if _, overflow := Fit(m1, dns.MaxMsgSize, tcp); overflow {
				promErrorCount.WithLabelValues("overflow").Inc()
				msgFail := new(dns.Msg)
				s.ServerFailure(msgFail, req)
				w.WriteMsg(msgFail)
				return
			}
		} else {
			// Overflow with udp always results in TC.
			Fit(m1, int(bufsize), tcp)
			if m1.Truncated {
				promErrorCount.WithLabelValues("truncated").Inc()
			}
		}
		// Still round-robin even with hits from the cache.
		// Only shuffle A and AAAA records with each other.
		if q.Qtype == dns.TypeA || q.Qtype == dns.TypeAAAA {
			s.RoundRobin(m1.Answer)
		}

		if err := w.WriteMsg(m1); err != nil {
			logf("failure to return reply %q", err)
		}
		metricSizeAndDuration(m1, start, tcp)
		return
	}

	for zone, ns := range *s.config.stub {
		if strings.HasSuffix(name, zone) {
			resp := s.ServeDNSStubForward(w, req, ns)
			if resp != nil {
				s.rcache.InsertMessage(cache.Key(q, dnssec, tcp), resp)
				metricSizeAndDuration(resp, start, tcp)
			}
			return
		}
	}

	// If the qname is local.ds.skydns.local. and s.config.Local != "", substitute that name.
	if s.config.Local != "" && name == s.config.localDomain {
		name = s.config.Local
	}

	if q.Qtype == dns.TypePTR && strings.HasSuffix(name, ".in-addr.arpa.") || strings.HasSuffix(name, ".ip6.arpa.") {
		resp := s.ServeDNSReverse(w, req)
		if resp != nil {
			s.rcache.InsertMessage(cache.Key(q, dnssec, tcp), resp)
			metricSizeAndDuration(resp, start, tcp)
		}
		return
	}

	if q.Qclass != dns.ClassCHAOS && !strings.HasSuffix(name, s.config.Domain) {
		resp := s.ServeDNSForward(w, req)
		if resp != nil {
			s.rcache.InsertMessage(cache.Key(q, dnssec, tcp), resp)
			metricSizeAndDuration(resp, start, tcp)
		}
		return
	}

	promCacheMiss.WithLabelValues("response").Inc()

	defer func() {
		if m.Rcode == dns.RcodeServerFailure {
			if err := w.WriteMsg(m); err != nil {
				logf("failure to return reply %q", err)
			}
			return
		}
		// Set TTL to the minimum of the RRset and dedup the message, i.e. remove identical RRs.
		m = s.dedup(m)

		minttl := s.config.Ttl
		if len(m.Answer) > 1 {
			for _, r := range m.Answer {
				if r.Header().Ttl < minttl {
					minttl = r.Header().Ttl
				}
			}
			for _, r := range m.Answer {
				r.Header().Ttl = minttl
			}
		}

		if dnssec {
			if s.config.PubKey != nil {
				m.AuthenticatedData = true
				s.Denial(m)
				s.Sign(m, bufsize)
			}
		}

		if tcp {
			if _, overflow := Fit(m, dns.MaxMsgSize, tcp); overflow {
				msgFail := new(dns.Msg)
				s.ServerFailure(msgFail, req)
				w.WriteMsg(msgFail)
				return
			}
		} else {
			Fit(m, int(bufsize), tcp)
			if m.Truncated {
				promErrorCount.WithLabelValues("truncated").Inc()
			}
		}
		s.rcache.InsertMessage(cache.Key(q, dnssec, tcp), m)

		if err := w.WriteMsg(m); err != nil {
			logf("failure to return reply %q", err)
		}
		metricSizeAndDuration(m, start, tcp)
	}()

	if name == s.config.Domain {
		if q.Qtype == dns.TypeSOA {
			m.Answer = []dns.RR{s.NewSOA()}
			return
		}
		if q.Qtype == dns.TypeDNSKEY {
			if s.config.PubKey != nil {
				m.Answer = []dns.RR{s.config.PubKey}
				return
			}
		}
	}
	if q.Qclass == dns.ClassCHAOS {
		if q.Qtype == dns.TypeTXT {
			switch name {
			case "authors.bind.":
				fallthrough
			case s.config.Domain:
				hdr := dns.RR_Header{Name: q.Name, Rrtype: dns.TypeTXT, Class: dns.ClassCHAOS, Ttl: 0}
				authors := []string{"Erik St. Martin", "Brian Ketelsen", "Miek Gieben", "Michael Crosby"}
				for _, a := range authors {
					m.Answer = append(m.Answer, &dns.TXT{Hdr: hdr, Txt: []string{a}})
				}
				for j := 0; j < len(authors)*(int(dns.Id())%4+1); j++ {
					q := int(dns.Id()) % len(authors)
					p := int(dns.Id()) % len(authors)
					if q == p {
						p = (p + 1) % len(authors)
					}
					m.Answer[q], m.Answer[p] = m.Answer[p], m.Answer[q]
				}
				return
			case "version.bind.":
				fallthrough
			case "version.server.":
				hdr := dns.RR_Header{Name: q.Name, Rrtype: dns.TypeTXT, Class: dns.ClassCHAOS, Ttl: 0}
				m.Answer = []dns.RR{&dns.TXT{Hdr: hdr, Txt: []string{Version}}}
				return
			case "hostname.bind.":
				fallthrough
			case "id.server.":
				// TODO(miek): machine name to return
				hdr := dns.RR_Header{Name: q.Name, Rrtype: dns.TypeTXT, Class: dns.ClassCHAOS, Ttl: 0}
				m.Answer = []dns.RR{&dns.TXT{Hdr: hdr, Txt: []string{"localhost"}}}
				return
			}
		}
		// still here, fail
		m.SetReply(req)
		m.SetRcode(req, dns.RcodeServerFailure)
		return
	}

	switch q.Qtype {
	case dns.TypeNS:
		if name != s.config.Domain {
			break
		}
		// Lookup s.config.DnsDomain
		records, extra, err := s.NSRecords(q, s.config.dnsDomain)
		if isEtcdNameError(err, s) {
			s.NameError(m, req)
			return
		}
		m.Answer = append(m.Answer, records...)
		m.Extra = append(m.Extra, extra...)
	case dns.TypeA, dns.TypeAAAA:
		records, err := s.AddressRecords(q, name, nil, bufsize, dnssec, false)
		if isEtcdNameError(err, s) {
			s.NameError(m, req)
			return
		}
		m.Answer = append(m.Answer, records...)
	case dns.TypeTXT:
		records, err := s.TXTRecords(q, name)
		if isEtcdNameError(err, s) {
			s.NameError(m, req)
			return
		}
		m.Answer = append(m.Answer, records...)
	case dns.TypeCNAME:
		records, err := s.CNAMERecords(q, name)
		if isEtcdNameError(err, s) {
			s.NameError(m, req)
			return
		}
		m.Answer = append(m.Answer, records...)
	case dns.TypeMX:
		records, extra, err := s.MXRecords(q, name, bufsize, dnssec)
		if isEtcdNameError(err, s) {
			s.NameError(m, req)
			return
		}
		m.Answer = append(m.Answer, records...)
		m.Extra = append(m.Extra, extra...)
	default:
		fallthrough // also catch other types, so that they return NODATA
	case dns.TypeSRV:
		records, extra, err := s.SRVRecords(q, name, bufsize, dnssec)
		if err != nil {
			if isEtcdNameError(err, s) {
				s.NameError(m, req)
				return
			}
			logf("got error from backend: %s", err)
			if q.Qtype == dns.TypeSRV { // Otherwise NODATA
				s.ServerFailure(m, req)
				return
			}
		}
		// if we are here again, check the types, because an answer may only
		// be given for SRV. All other types should return NODATA, the
		// NXDOMAIN part is handled in the above code. TODO(miek): yes this
		// can be done in a more elegant manor.
		if q.Qtype == dns.TypeSRV {
			m.Answer = append(m.Answer, records...)
			m.Extra = append(m.Extra, extra...)
		}
	}

	if len(m.Answer) == 0 { // NODATA response
		StatsNoDataCount.Inc(1)
		m.Ns = []dns.RR{s.NewSOA()}
		m.Ns[0].Header().Ttl = s.config.MinTtl
	}
}