Discussion:
Seeking info about 'best practice' for multihomed (or not) DCs
(too old to reply)
Eggy
18 years ago
Permalink
After encountering a problem that occurred when I introduced a multihomed DC
into my network I learned that it is, apparently, not advisable to use
multihoming on a DC. Can you refer me to any 'official' documentation on
this practice?

Thanks!
Pete

PS - The problem that popped-up regards the 'net view' command. After
installing a new DC things worked fine until I enabled it's second NIC.
Afterward, on certain machines, 'net view' broke, complaining that a "System
error 6118 has occurred". It might be relevent that the system on which net
view failed is a Windows 2000 DC (the new DC is Win 2003). I resolved the
problem by disabling NetBIOS over TCP/IP on the second NIC.
Phillip Windell
18 years ago
Permalink
157025 - Default Gateway Configuration for Multihomed Computers
http://support.microsoft.com/default.aspx?scid=kb;en-us;157025&Product=win2000

159168 - Multiple Default Gateways Can Cause Connectivity Problems
http://support.microsoft.com/kb/159168/EN-US/

272294 - Active Directory Communication Fails on Multihomed Domain
Controllers
http://support.microsoft.com/default.aspx?scid=kb;en-us;272294

191611 - Symptoms of Multihomed Browsers
http://support.microsoft.com/default.aspx?scid=kb;EN-US;191611
--
Phillip Windell
www.wandtv.com

The views expressed, are my own and not those of my employer, or Microsoft,
or anyone else associated with me, including my cats.
-----------------------------------------------------
...
Eggy
18 years ago
Permalink
Phillip (and All),

Thanks. The KB's you cited are helpful. Part of my trouble is that many of
the issues with multihoming are due to limitations of NT & 2000. I plan to
be rid of all 2000 and earlier servers soon, and am trying to develop a clear
understanding of multihoming in 2003-only environment.

Sorry to belabor the point, but please let me inquire further. KB 191611
states "The domain master browser service properly binds to only one network
interface. The PDC serves the role of the domain master browser. We suggest
that your PDC is not multihomed." Can you help me determine if this advice
is applicable to a 2003-only environment? When I attain 2003-only status
will I be OK with a multihomed PDC?

BTW, in my case, multihoming is only for redundancy; it is not used for
RRAS, and RRAS is not active on any server.

Thanks Again!
Eggy
...
Phillip Windell
18 years ago
Permalink
Post by Eggy
Thanks. The KB's you cited are helpful. Part of my trouble is that many of
the issues with multihoming are due to limitations of NT & 2000. I plan to
be rid of all 2000 and earlier servers soon, and am trying to develop a clear
understanding of multihoming in 2003-only environment.
It will not change with 2003 or R2 or anything in the near future that I
have ever heard about.
Post by Eggy
BTW, in my case, multihoming is only for redundancy;
Multi-Homing does NOT provide proper redundancy,...it only screws things up.
Redundancy at that level is done with "Nic Teaming". With "Nic Teaming" the
two Nics behave as a single virtual interface so it is therefore
single-homed and not multi-homed. Nic Teaming requires the Nics and the
software designed with this abilty.
--
Phillip Windell
www.wandtv.com

The views expressed, are my own and not those of my employer, or Microsoft,
or anyone else associated with me, including my cats.
-----------------------------------------------------
Eggy
18 years ago
Permalink
Phillip,

Thanks again! I appreciate the clarification.

Eggy
...
Phillip Windell
18 years ago
Permalink
No problem.
Although I haven't bothered to mess with it myself,..I think a lot of the
news nic in the new servers can do Teaming if you want to look into that.
--
Phillip Windell
www.wandtv.com

The views expressed, are my own and not those of my employer, or Microsoft,
or anyone else associated with me, including my cats.
-----------------------------------------------------
...
Bill Grant
18 years ago
Permalink
No, going all server 2003 will not mean that the problem goes away. If you
use Netbios over TCP/IP (with or without WINS) you still have the problems
which you had in NT. Even if yo get rid of Netbt, you still strike similar
problems because of dynamic DNS.

The basic problem is that, it a server has more than one interface, you
end up with two IP addresses (linked to two different interfaces) which are
associated with the same computer name. If a machine tries to access the
server by name and gets the "wrong" IP you can get strange things happening.
That is basically what causes the browser problems with Netbt, and why
disabling Netbios over TCP/IP on one NIC solves the problem.
...
Ace Fekay [MVP]
18 years ago
Permalink
...
Phillip and Bill provided some good suggestions and documentation. I would
like to reiterate that a multihomed DC is not advisable unless the NICs are
teamed. Unteamed NICs in a DC is inviting trouble, whether with RRAS or not.

However, if YOU insist on using a multhomed DC, below is a re-print of my
notes on how to PROPERLY configure a mutlihomed DC. Please read each step
carefully to understand why the settings are being made. AThere are also
registry entries to be modified. Prior to making any registry modification,
make sure you back up the registry first.

Honestly, in my opinion, it rally is NOT worth altering a DC's default
functionality to force mutlihoming to work, for whatever reason. - Good
luck.

---------------------------------
********************************
Multihomed DCs, DNS, RRAS servers.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++++++++++++++++++++++++++++++
Below are the manual steps in more detail, which I had outlined in the above
paragraph:

Honestly, multi-homed DCs are not recommended because of the associated
issues that can occur, as you've encountered. We usually recommend
purchasing an inexpensive Linksys, DLink, etc, Cable/DSL router to perform
NAT for you, take out the extra NIC off the DC, but still let the DC handle
DHCP (and not the router).

Little background on AD and DNS:
First, just to get this out of the way, if you have your ISP's DNS addresses
in your IP configuration (DCs and clients), they need to be REMOVED.

If the ISP's DNS is in there, this will cause additional problems.

Also, AD registers certain records in DNS in the form of SRV records that
signify AD's resource and service locations. When there are multiple NICs,
each NIC registers. IF a client, or another DC queries DNS for this DC, it
may get the wrong record. One factor controlling this is Round Robin. If a
DC or client on another subnet that the DC is not configured on queries for
it, Round Robin will kick in offering one or the other. If the wrong one
gets offered, it may not have a route to it. On the other hand, Subnetmask
Priortization will ensure a querying client will get an IP that corresponds
to the subnet it's on, which will work. To insure everything works, stick
with one NIC.

Since this DC is multi-homed, it requires additional configuration to
prevent the public interface addresses from being registered in DNS. This
creates a problem for internal clients locating AD to authenticate and find
other services and resources such as the Global Catalog, file sharing and
the SYSVOL DFS share and can cause GPO errors with Userenv 1000 events to be
logged, authenticating to shares and printers, logging on takes forever,
among numerous other issues.

But if you like, there are some registry changes to eliminate the
registration of the external NIC. Here's the whole list of manual steps to
follow.

But believe me, it's much easier to just get a separate NAT device or
multihome a non-DC then having to alter the DC. - Good luck!

1. Insure that all the NICS only point to your internal DNS server(s) only
and none others, such as your ISP's DNS servers' IP addresses.

2. In Network & Dialup properties, Advanced Menu item, Advanced Settings,
move the internal NIC (the network that AD is on) to the top of the binding
order (top of the list).

3. Disable the ability for the outer NIC to register. The procedure, as
mentioned, involves identifying the outer NIC's GUID number. This link will
show you how:
246804 - How to Enable-Disable Windows 2000 Dynamic DNS Registrations (per
NIC too):
http://support.microsoft.com/?id=246804

4. Disable NetBIOS on the outside NIC. That is performed by choosing to
disable NetBIOS in IP Properties, Advanced, and you will find that under the
"WINS" tab. You may want to look at step #3 in the article to show you how
to disable NetBIOS on the RRAS interfaces if this is a RRAS server.
296379 - How to Disable NetBIOS on an Incoming Remote Access Interface
[Registry Entry]:
http://support.microsoft.com/?id=296379

Note: A standard Windows service, called the "Browser service", provides the
list of machines, workgroup and domain names that you see in "My Network
Places" (or the legacy term "Network Neighborhood"). The Browser service
relies on the NetBIOS service. One major requirement of NetBIOS service is a
machine can only have one name to one IP address. It's sort of a
fingerprint. You can't have two brothers named Darrell. A multihomed machine
will cause duplicate name errors on itself because Windows sees itself with
the same name in the Browse List (My Network Places), but with different
IPs. You can only have one, hence the error generated.

5. Disable the "File and Print Service" and disable the "MS Client Service"
on the outer NIC. That is done in NIC properties by unchecking the
respective service under the general properties page. If you need these
services on the outside NIC (which is unlikely), which allow other machines
to connect to your machine for accessing resource on your machine (shared
folders, printers, etc.), then you will probably need to keep them enabled.

6. Uncheck "Register this connection" under IP properties, Advanced
settings, "DNS" tab.

7. Delete the outer NIC IP address, disable Netlogon registration, and
manually create the required records

a. In DNS under the zone name, (your DNS domain name), delete the outer
NIC's IP references for the "LdapIpAddress". If this is a GC, you will need
to delete the GC IP record as well (the "GcIpAddress"). To do that, in the
DNS console, under the zone name, you will see the _msdcs folder. Under
that, you will see the _gc folder. To the right, you will see the IP address
referencing the GC address. That is called the GcIpAddress. Delete the IP
addresses referencing the outer NIC.

i. To stop these two records from registering that information,
use the steps provided in the links below:
Private Network Interfaces on a Domain Controller Are Registered in
DNShttp://support.microsoft.com/?id=295328

ii. The one section of the article that disables these records is
done with this registry entry:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters
(Create this Multi-String Value under it):
Registry value: DnsAvoidRegisterRecords
Data type: REG_MULTI_SZ
Values: LdapIpAddress
GcIpAddress

iii. Here is more information on these and other Netlogon Service records:
Restrict the DNS SRV resource records updated by the Netlogon service
[including GC]:
http://www.microsoft.com/technet/treeview/default.asp?url=/technet/prodtechnol/windowsserver2003/proddocs/standard/sag_dns_pro_no_rr_in_ad.asp

b. Then you will need to manually create these two records in DNS with
the IP addresses that you need for the DC. To create the

LdapIpAddress, create a new host under the domain, but leave the "hostname"
field blank, and provide the internal IP of the DC, which results in a
record that looks like:
(same as parent) A 192.168.5.200 (192.168.5.200 is used for illustrative
purposes)

i. You need to also manually create the GcIpAddress as well, if
this is a GC. That would be under the _msdcs._gc SRV record under the zone.
It is created in the same fashion as the LdapIpAddress mentioned above.

8. In the DNS console, right click the server name, choose properties, then
under the "Interfaces" tab, force it only to listen to the internal NIC's IP
address, and not the IP address of the outer NIC.

9. Since this is also a DNS server, the IPs from all NICs will register,
even if you tell it not to in the NIC properties. See this to show you how
to stop that behavior (this procedure is for Windows 2000, but will also
work for Windows 2003):
275554 - The Host's A Record Is Registered in DNS After You Choose Not to
Register the Connection's Address:
http://support.microsoft.com/?id=275554

10. If you haven't done so, configure a forwarder. You can use 4.2.2.2 if
not sure which DNS to forward to until you've got the DNS address of your
ISP.
How to set a forwarder? Good question. Depending on your operating
system,choose one of the following articles:

300202 - HOW TO: Configure DNS for Internet Access in Windows 2000
http://support.microsoft.com/?id=300202&FR=1

323380 - HOW TO: Configure DNS for Internet Access in Windows Server 2003
(How to configure a forwarder):
http://support.microsoft.com/d/id?=323380

Active Directory communication fails on multihomed domain controllers
http://support.microsoft.com/kb/272294


<==*** Some additional reading ***==>
More links to read up and understand what is going on:

292822 - Name Resolution and Connectivity Issues on Windows 2000 Domain
Controller with Routing and Remote Access and DNS Insta {DNS and RRAS and
unwanted IPs registering]:
http://support.microsoft.com/?id=292822

Active Directory communication fails on multihomed domain controllers
http://support.microsoft.com/kb/272294

246804 - How to enable or disable DNS updates in Windows 2000 and in Windows
Server 2003
http://support.microsoft.com/?id=246804

295328 - Private Network Interfaces on a Domain Controller Are Registered in
DNS
[also shows DnsAvoidRegisterRecords LdapIpAddress to avoid reg sameasparent
private IP]:
http://support.microsoft.com/?id=295328

306602 - How to Optimize the Location of a DC or GC That Resides Outside of
a Client's
Site [Includes info LdapIpAddress and GcIpAddress information and the SRV
mnemonic values]:
http://support.microsoft.com/?id=306602

825036 - Best practices for DNS client settings in Windows 2000 Server and
in Windows Server 2003 (including how-to configure a forwarder):
http://support.microsoft.com/default.aspx?scid=kb;en-us;825036

291382 - Frequently asked questions about Windows 2000 DNS and Windows
Server 2003 DNS
http://support.microsoft.com/?id=291382

296379 - How to Disable NetBIOS on an Incoming Remote Access Interface
[Registry Entry]:
http://support.microsoft.com/?id=296379


Rid Pool Errors and other mutlhomed DC errors, and how to configure a
multihomed DC, Ace Fekay, 24 Feb 2006
http://www.ureader.com/message/3244572.aspx

_________________________
--
Regards,
Ace

This posting is provided "AS-IS" with no warranties or guarantees and
confers no rights.

Ace Fekay, MCSE 2003 & 2000, MCSA 2003 & 2000, MCSE+I, MCT,
MVP Microsoft MVP - Directory Services
Microsoft Certified Trainer

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Eggy
18 years ago
Permalink
Phillip, Bill and Ace,

Thank you so much for providing this info. It is exactly what I was
seeking. And exactly what I suspected! -- thanks for the confirmation.

I'll modify my system until I have a chance to investigate teaming.

Thanks Again!
Pete
...
Phillip Windell
18 years ago
Permalink
Ok, good luck with it!
--
Phillip Windell
www.wandtv.com

The views expressed, are my own and not those of my employer, or Microsoft,
or anyone else associated with me, including my cats.
-----------------------------------------------------
...
Ace Fekay [MVP]
18 years ago
Permalink
Post by Phillip Windell
Ok, good luck with it!
Yes, good luck too!

Ace

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