How could I make a mDNS Query with Pcap.net? - vb.net

Question

Problem: I'm looking to make a mDNS packet, while having searching stackflow for options. I tried bonjour and some wrappers but had very limited success, especially when I requested a second time and get socket binding complaints (Which, of course, may have been my code not them).
Since VB.net didn't have a really editable dnsquery that I know of, I'm using the DNS layer in the build DNS packet in pcapdotnet and just kind of making the packet myself layer by layer. I'm thinking it's a good alternative, but I'm kind of lost on how I would do it.
Here's the question we want:
q_name = new QuestionName("_axis-video._tcp.local"),
q_type = QueryConstants.Question.QuestionType.PTR,
q_class = QueryConstants.Question.QuestionClass.IN
Here's my edited BuildDNSPacket function from their standard:
Private Shared Function BuildDnsPacket(destmac As String, domainName As String) As Packet
'get source MAC address of PC
Dim nic = System.Net.NetworkInformation.NetworkInterface.GetAllNetworkInterfaces()
Dim source As String = nic(0).GetPhysicalAddress().ToString
Dim sourcearray As Byte() = System.Text.Encoding.ASCII.GetBytes(source)
'format
Dim sourceMacStr As String = ""
For i As Integer = 0 To sourcearray.Count - 1 Step 2
sourceMacStr += Chr(sourcearray(i)) & Chr(sourcearray(i + 1)) & ":"
Next
' Will be filled automatically.
Dim ethernetLayer As New EthernetLayer() With { _
.Source = New MacAddress(sourceMacStr.Substring(0, 17)), _
.Destination = New MacAddress(destmac), _
.EtherType = EthernetType.None _
}
' Will be filled automatically.
Dim ipV4Layer As New IpV4Layer() With { _
.Source = New IpV4Address("1.2.3.4"), _
.CurrentDestination = New IpV4Address(destmac), _
.Fragmentation = IpV4Fragmentation.None, _
.HeaderChecksum = Nothing, _
.Identification = 123, _
.Options = IpV4Options.None, _
.Protocol = Nothing, _
.Ttl = 100, _
.TypeOfService = 0 _
}
' Will be filled automatically.
Dim udpLayer As New UdpLayer() With { _
.SourcePort = 5353, _
.DestinationPort = 5353, _
.Checksum = Nothing, _
.CalculateChecksumValue = False _
}
Dim dnsLayer As New DnsLayer() With { _
.Id = 0, _
.IsResponse = False, _
.OpCode = DnsOpCode.Query, _
.IsAuthoritativeAnswer = False, _
.IsTruncated = False, _
.IsRecursionDesired = False, _
.IsRecursionAvailable = False, _
.FutureUse = False, _
.IsAuthenticData = False, _
.IsCheckingDisabled = False, _
.ResponseCode = DnsResponseCode.NoError, _
.Queries = {New DnsQueryResourceRecord(New DnsDomainName(domainName), DnsType.Ptr, DnsClass.Any)}, _
.Answers = Nothing, _
.Authorities = Nothing, _
.Additionals = Nothing, _
.DomainNameCompressionMode = DnsDomainNameCompressionMode.All _
}
Dim builder As New PacketBuilder(ethernetLayer, ipV4Layer, udpLayer, dnsLayer)
Return builder.Build(DateTime.Now)
End Function
The main differences is my changing the DnsType to PTR and the port to 5353.
Question: What else should I add or change to make it mDNS? What could I put into the domainName? Should I vary the dnsclass?
All or any suggestions are definitely welcomed.

Answer 1

I am answering my question in case others who need to do mDNS in vb.net needs this:
Solution: I didn't need to add anything to the DNS layer to make this work. I changed the DNS layer to below:
Dim dnsLayer As New DnsLayer() With { _
.Id = 0, _
.IsResponse = False, _
.OpCode = DnsOpCode.Query, _
.IsAuthoritativeAnswer = False, _
.IsTruncated = False, _
.IsRecursionDesired = False, _
.IsRecursionAvailable = False, _
.FutureUse = False, _
.IsAuthenticData = False, _
.IsCheckingDisabled = False, _
.ResponseCode = DnsResponseCode.NoError, _
.Queries = {New DnsQueryResourceRecord(New DnsDomainName(domainName), DnsType.Ptr, DnsClass.Any)}, _
.Answers = Nothing, _
.Authorities = Nothing, _
.Additionals = Nothing, _
.DomainNameCompressionMode = DnsDomainNameCompressionMode.All _
}
I made the output address of the Ipv4 layer to be the multicast address of "224.0.0.251", changed my ports to 5353, and used the domain name of the question I listed above.
Here's a wireshark to show the responses: