The Mole #19: Technical Answers from Inside Microsoft - BDC Needs, DHCP Importing, Backtalk
October 11, 1999
Editors Note The questions and answers below are from the Inside Microsoft column that appears regularly on the TechNet Web site at the following location: https://www.microsoft.com/technet/community/columns/insider/default.mspx. To find out how to submit questions of your own, see the end of this article or go to https://www.microsoft.com/technet/community/columns/insider/default.mspx.
The TechNet Mole provides expert answers from deep within Microsoft to questions from IT professionals. This installment focuses on these issues:
Why You Need that BDC
Importing a DHCP Database, or Is this the World's Longest Acronym
Backtalk!
Windows NT Memory BleedThe Lowdown on Load Balancing: Three Readers Speak
On This Page
In Praise of Redundancy
Importing a DHCP database
Backtalk! You guys RAWK
Got Questions? Mail the Mole
Credits
In Praise of Redundancy
Dear Mole,
I hear a lot about clustering and Stand-by Servers but can't seem to find much material on the proper implementation of these solutions. I have one client in particular that wants to have a fully redundant backup server that can take over within seconds in the event that their PDC fails. This client has a very small LAN with only one server and 26 Win95hosts at this time. The company has a desire to keep the costs to a minimum so I was thinking of setting up a BDC with similar storage capacity and using WinAT to schedule copies of their data at regular intervals and mapping the backup data directories to the clients. This is obviously a shoddy solution for seamless operation, and since data directory contains 4.2GB the copy processes would seriously degrade network performance. Can you help point me in the right direction for setting up a pair of redundant servers that would provide nearly seamless production should one of the pair fail.
Paul
Dear Paul,
It sounds to Mole as if your first task here is more evangelical than technical. Like, how to convince a cost-conscious (should we say, penny pinching?) client that using a BDC in a Windows NT network is as essential as an umbrella in Seattle, as snow tires in Maine, as sunscreen in Belize? The fact is, the cost of downtime if their PDC goes south is a whole lot more than the cost of that second server will ever be. It's spelled I-N-S-U-R-A-N-C-E. Only a fool drives, or computes, without it. Take it from Mother Mole.
That said, let's look more closely at what your client wants and what his options are, keeping in mind that he's asking one server to act in two mission-critical capacities—primary domain controller and file server.
Protecting your Windows NT Operating System
As you know, your domain controller takes care of Windows NT business—little things like user account validation, group membership, and access rights. Right off the top of his nose, Mole can think of two different kinds of nasties that would make any client wish he'd sprung for a BDC. The first is hardware failure. Sure, it may be under warranty, but a fried disk is still fried. Number two is what they like to call in contracts "acts of God," which Mole understands to be things like earthquake, fire, and flood. You know, when the i-beam comes crashing down and squishes your computer.
Disk problems can be mitigated using RAID technologies, like mirroring the system partition--small comfort in one of those end-of-the-world scenarios, but quite helpful if the disk drive head containing the NT operating system crashes. Think of RAID as cheap insurance. For the cost of a hard drive and a controller, you can still run your network if the building falls down on top of your PDC. Providing, of course, you were smart enough to put the BDC in a different building. Got that, sport?
Protecting your Data
Similarly, RAID can be used for protecting the user's data. You can use Mirroring (RAID Level 1) or Stripe Sets with Parity (RAID level 5) to protect data. Stripe sets alone (RAID level 0) do not provide fault tolerance. There are benefits and drawbacks to both RAID 1 and RAID 5—see Chapter 7 - Protecting Data of the "Windows NT Server 4.0 Concepts and Planning Guide" for more details. Note that recovering from a failed drive using mirroring requires some operator intervention—we're talking more than "seconds" here.
You can also think about Windows NT Directory Replication. What Directory Replication does is copy changes to data made on the source machine to another location (like another data server), either as soon as the data is changed or after the subdirectory containing the data has been stable for two minutes. Using WinAT to copy data from one server to another seems to me to be excessive. All you really want to do is copy the data that has changed, right? More information on Directory Replication can be found in Chapter 4 - Managing Shared Resources and Resource Security of the "Windows NT Server 4.0 Concepts and Planning Guide."
And then there's clustering, a great technology for fast failovers. Microsoft's clustering technology complements other high-availability techniques like data mirroring, RAID disk protection, uinterruptible power supplies, and duplicated hardware (e.g. fans and network interface cards.) Clustering automatically restores user access to data and services following the failure of individual applications or servers. Clustering and other high-availability technology should be used together with smart data backup and disaster-site recovery procedures to keep your system up and running 24x7. Cluster Server runs on Windows NT 4.0 Server Enterprise Edition.
Herewith, some hot links to feed your cluster server hungers:
Importing a DHCP database
Dear Mole,
Is there any way to take our DHCP database and import it into a more manageable form, (such as an Access Database or a SQL Database.)
We have a web app that would benefit from the client information housed in the DHCP database but we haven't been able to figure out any way to extract it. We are not even sure if it is possible (in the practical sense.)
Roman T. Burchart, Network Support Technician, National Heritage Academies
Roman,
Try DHCPCMD (how many letters can you remember at one time?) from the Windows NT 4.0 Server Resource Kit. You should be able to redirect the output to a text file using the ">" from the command line, just like in the olden days where you would pipe a directory listing to a text file by entering "dir *.* > myfiles.txt".
Ahhh, the good old days. When code was code and coders were well, never mind.
DHCPCMD has several commands, including the following, which provides information on active leases.
EnumClients
Lists the lease information in a different format.
Syntax
dhcpcmd scope_address enumclients [-v | -h]
where
Option |
Meaning |
|---|---|
-v |
Lists detailed lease information. |
-h |
Lists lease information with hardware information. |
Example
dhcpcmd 127.0.0.1 enumclients 11.101.0.0 -h
DHCPCMD is located on MS Windows NT 4.0 Resource Kit, Supplement 4 Utilities.
No. Don't thank me. Your happiness is my reward.
Backtalk! You guys RAWK
Mole wants you to know he considers each and every one of his readers a colleague. Especially those of you who bothered to talk back to recent columns, with these hot tips.
Backtalk 1.0 — Windows NT Memory Bleed
Hey, Mole.
Try using "Empty.exe" located in the NT Resource Kit. Works for me.
David Michelson, MCSE
David,
Thanks for the tip. A bit more information:
EMPTY frees the working set of a specified task or process. Run Empty from the command line. At the prompt, type:
empty { PID | progname }
PID is Product Identification number. Of course, using EMPTY frees the working set of a task or process – it doesn't help with determining what is causing the memory bleed, but then, there are probably times you don't really care.
Backtalk 2.0 3 NICs, one IP address
Mole:
Re: "3 NICs, one IP address" originally posted from SSgt. Kevin Fox of Hill ** AFB
Actually, reading the specs on the Intel network cards that came in my Compaq Proliant 3000, there is hardware support for 3 IP addresses on the same network card. What happens is the network cards are actually bundled into a "NIC Cluster" of sorts. The hardware and configuration of the network cards handles this (it is not an NT issue).
There are some requirements that go with this, like your network switch must be able to handle this as it is a combined effort between the switch, the network cards and the drivers installed on the server. This provides load balancing for high bandwidth, as well as redundancy to avoid failure on mission critical servers.
I don't know if 3Com can do this, but it would be something to investigate with your network vendor.
John M. Abbott, MCSE, Network/Desktop Support Technician, Sun Chemical, Muskegon
Backtalk 2.1
Mole:
You replied that there's no way to do this, but that TCP/IP under Windows NT will utilize a randomizing algorithm to accomplish load balancing. While true, I don't think that's what Kevin was looking for. I believe that he was referring to 3Com's Load Balancing feature that is supported on their EtherLink Server NICs. From 3Com's Web site:
"To enhance network performance, the Fast EtherLink Server NIC supports Load Balancing, a DynamicAccess® software feature that boosts server throughput by intelligently and automatically distributing packet transfer among multiple NICs that have been aggregated into one virtual NIC. To the server, these multiple NICs appear as a single network interface. The result is higher bandwidth between the server and switch, eliminating bottlenecks at the server. "
I think Kevin may be assuming that the 3Com Desktop NICs will do this too, which they won't.
Incidentally, we're doing something similar here with Intel Server Adapters. The main difference is that Intel's drivers support Cisco's FastEtherChannel protocol, so the load balancing is done at a hardware level. Our main file server is utilizing two Intel Dual-Port Server Adapters, with all four 100Mbps channels combined into one FastEtherChannel. TCP/IP sees the four ports as one device, and the Cisco 6509 they connect to sees treats them as one pipe. It's a great solution for reliability and throughput.
Intel also supports Intel Link Aggregation, for connection to Intel Express Switches, and Adaptive Load Balancing, for connection to other switched devices (which looks very similar to the 3Com Load Balancing solution).
Chris Everett, Network Analyst, OrCAD, Inc.
Backtalk 2.2
Dear Mole,
I was reading the July 19 Mole column and saw the question regarding 3 NICs and one IP Address. While your answer is correct from a Microsoft point of view, it is incorrect from a Compaq point of view. The problem is that Kevin was using 3COM NIC's. While I personally love 3COM products, a Compaq NIC can't be beat in a Compaq Server, as he indicated he is using a Proliant 5000. Compaq will allow you to "bind" multiple network cards to act as a single card. This will work in an IP environment, I know because I'm doing it.
Christopher Kam, MCSE and Mega-Geek
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Credits
Mole thanks his esteemed collaborator, Lon Collins.
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