Re: Name resolution vs. multiple NICs

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From: Eugene Gershnik (gershnik_at_hotmail.com)
Date: 01/13/05 

Date: Wed, 12 Jan 2005 21:04:49 -0800

Dean Roddey wrote:
>> First, I don't understand the term "canonical name". What is it
>> and how is it defined?
>> Second, how exactly do you obtain it from a NetBIOS name?
>
> It's defined in the Windows API getaddrinfo().

As a matter of fact it isn't. All MSDN says that it can return "canonical
name" without explaining what it is.

> It returns the FQDN.

Let's assume that for the time being, though I wouldn't rely on that.

> Even on a domain based system, the short name of a machine will
> work on the local machine.

If you mean it can be resolved then this is so by definition.

> You can use getaddrinfo() to make sure
> that you have the FQDN.

Not really. All you can physically get is what is FQDN as it appears to
_your_ machine. It doesn't have to be the same as FQDN that the target
machine itself sees. For example I may have a private DNS server that will
tell me that my FQDN is "host.domain.com" while you will only see me by my
netbios name "host".

>> Third, you still didn't explain what exactly _does not work_ for
>> you. Do you try to connect() and get an error back? If so what
>> error is it? Is it something else.
>
> Actually I did earlier, but the issue is that when I resolve the
> FQDN (the canonical name), it's not right

Can you ping it? If so the name is right. There is no such thing as an
"illegal name" (see below)

> because it comes back
> with their ISP's domain suffix attached to it, despite the fact
> that they are in a Workgroup.

We have been through this before don't we. Being "in a workgroup" is
orthogonal to TCP/IP name resolution. Most likely their computer
configuration tells them that they are in .isp.com and that's what they see.
Exactly as the scenario above.

> That name cannot then be resolved to
> a numeric address since it's not legal within their local network.

Names are only legal or illegal on a single host not "on network". Names are
translated to IPs by each _source_ host based on the information available
to it. If they can ping _themselves_ at host.isp.com then the name is legal.
If _you_ can't ping them by the same name it means that name resolution
available to you differs from theirs.

> This only seems to happen if two NICs are present and DHCP is being
> used to set them up. There is nothing in the DHCP server that sets
> any domain suffix.

And yet in another post you say

> When they do ipconfig /all, they are seeing connection specfiic domain
> suffixes show up, and that suffix of course is the ISP's domain.

which means that something does set the suffix for them. Most likely they
have the suffix hardcoded in the computer name (Right-click My
Computer/Properties/Computer Name/Change.../More...)

What I don't understand is why you go through all this gyrations to discover
the correct FQDN. If you can see them by the NetBIOS name isn't this enough? 

--
Eugene

Relevant Pages

  • Re: What is FQDN ?
    ... There is much to learn about DNS itself. ... Computer name/only DC1DNSAD and next line which is Domain ... Connection-specific DNS Suffix. ... Here if you put NetBios Name a Name of your Computer that you have ...
    (microsoft.public.windows.server.dns)
  • Re: Weird Behaviour Accessing MS CA Web Site
    ... I've tried adding FQDN and NETBIOS into intranet ... When you use IP you are forcing that Kerberos not be used. ... is configured to record login failures? ...
    (microsoft.public.windows.server.security)
  • Re: Cannot Use LAN IP Addresses
    ... I haven't seen problems with Netbios names,...they usually work. ... recognized as a FQDN as opposed to a Netbois name is by the fact that the ... Phillip Windell www.wandtv.com "A.Klimkin" wrote in message ... >> after they are resolved to an IP#,...so they always are proccessed by the>> proxying service. ...
    (microsoft.public.isa.clients)
  • Re: Map the FQDN to a content source issue
    ... This error is usually because of the proxy settings. ... > content sources to the netbios name. ... > pointing the FQDN to the internal IP returns an error in the gatherer log ...
    (microsoft.public.sharepoint.portalserver)
  • Re: Cannot Use LAN IP Addresses
    ... I haven't seen problems with Netbios names,...they usually work. ... recognized as a FQDN as opposed to a Netbois name is by the fact that the ... Phillip Windell www.wandtv.com "A.Klimkin" wrote in message ... >> after they are resolved to an IP#,...so they always are proccessed by the>> proxying service. ...
    (microsoft.public.isaserver)