name:                    "large request edns",
			host:                    "giant.",
			expectResolutionFailure: dns.RcodeSuccess,
			expected:                giantResponse,
			modifyReq: func(msg *dns.Msg) {
				msg.SetEdns0(dns.MaxMsgSize, false)
			},
		},
		{
			name:                    "large request truncated",
			host:                    "giant-tc.",
			expectResolutionFailure: dns.RcodeSuccess,

		return 0, nil, nil, err
	}

	// Accept packets up to maxDNSPacketSize.  RFC 6891.
	if err := b.StartAdditionals(); err != nil {
		return 0, nil, nil, err
	}
	var rh dnsmessage.ResourceHeader
	if err := rh.SetEDNS0(maxDNSPacketSize, dnsmessage.RCodeSuccess, false); err != nil {
		return 0, nil, nil, err
	}
	if err := b.OPTResource(rh, dnsmessage.OPTResource{}); err != nil {
		return 0, nil, nil, err
	}

				}
			}
		} else if s == "192.0.2.1:53" {
			if q.Questions[0].Type == dnsmessage.TypeA && strings.HasPrefix(q.Questions[0].Name.String(), "empty.com.") {
				var edns0Hdr dnsmessage.ResourceHeader
				edns0Hdr.SetEDNS0(maxDNSPacketSize, dnsmessage.RCodeSuccess, false)

				r.Additionals = []dnsmessage.Resource{
					{
						Header: edns0Hdr,
						Body:   &dnsmessage.OPTResource{},
					},
				}
			}
		}

const (
	edns0Version = 0

	edns0DNSSECOK     = 0x00008000
	ednsVersionMask   = 0x00ff0000
	edns0DNSSECOKMask = 0x00ff8000
)

// SetEDNS0 configures h for EDNS(0).
//
// The provided extRCode must be an extended RCode.
func (h *ResourceHeader) SetEDNS0(udpPayloadLen int, extRCode RCode, dnssecOK bool) error {
	h.Name = Name{Data: [255]byte{'.'}, Length: 1} // RFC 6891 section 6.1.2
	h.Type = TypeOPT