Devices with no hostname cause DHCP server not to bind on server restart

[PonchoPowers]

An exception is thrown when enabling the default scope after a reboot of the physical server when devices with no hostname have already been offered a lease that is now saved to the config.

I've tracked it down to the following:

DnsClient.IsDomainNameValid(name, true);

The lease hostname is null when saved...

As you can see in the following, I have two devices on my network which don't have a hostname, not sure if this is normal or not:

[PonchoPowers]

The following suggests that the domain if empty is the root zone, but in this cause the same method is being used to test hostnames for devices.

if (domain.Length == 0)
  return true; //domain is root zone

So I'm not really sure how you want to fix this as I'm not sure the following is really valid either.

if (domain == null)
  return **???**;

Setting HostName to an empty string would be a hack as it is null as there is no hostname.

So I propose the following fixes:

Change:

_authoritativeZoneRoot.SetRecords(lease.HostName, DnsResourceRecordType.A, scope.DnsTtl, new DnsResourceRecordData[] { new DnsARecord(lease.Address) });

to:

if (lease.HostName != null)
  _authoritativeZoneRoot.SetRecords(lease.HostName, DnsResourceRecordType.A, scope.DnsTtl, new DnsResourceRecordData[] { new DnsARecord(lease.Address) });

And change:

_authoritativeZoneRoot.SetRecords(Scope.GetReverseZone(lease.Address, 32), DnsResourceRecordType.PTR, scope.DnsTtl, new DnsResourceRecordData[] { new DnsPTRRecord(lease.HostName) });

to:

if (lease.HostName != null)
  _authoritativeZoneRoot.SetRecords(Scope.GetReverseZone(lease.Address, 32), DnsResourceRecordType.PTR, scope.DnsTtl, new DnsResourceRecordData[] { new DnsPTRRecord(lease.HostName) });

You might want to check this first to make sure it doesn't break anything as my knowledge of network technology is rubbish.

[ShreyasZare]

Thanks for the debugging. This can be fixed in UpdateDnsAuthZone() with below check:

if (string.IsNullOrEmpty(lease.HostName))
                return;

[PonchoPowers]

Just tested, the fix you proposed works for me, much simpler than my solution.

[ShreyasZare]

Technitium DNS Server v4.1 is now available that fixes this issue.