Multiple NICs

Discussion in 'Server Networking' started by Brian, Nov 16, 2004.

  1. Brian

    Brian Guest

    I am running windows 2003 server.

    I have two servers. Server A is my main server. Server B is my
    backup/redundancy server. I am mirroring Server A to Server B.

    I have multiple network cards in each server. In Server A, one card goes to
    the LAN, the other directly to Server B. Ditto in Server B, except it goes
    directly to Server A.

    I have assigned the LAN card in each server, an IP number on the LAN subnet.
    I have assigned a different subnet IP number to the network card which is
    directly connected to each server.

    I am unable to make the data flow down the directly connected network cards
    from each server. Instead it flows around through the LAN to each server.

    Does anybody have any idea about how to make it instead flow down the
    directly connected network cards/cable?

    I can ping each server from the other, using the directly connected ip
    numbers, if the LAN cable is disconnected, so they are communicating with
    each other. So why can't I make the data flow through that interface?
    Brian, Nov 16, 2004
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  2. Brian

    Bill Grant Guest

    How are you sending the data? By name? If the name resolves to the LAN
    IP, then that is the way the data will go.
    Bill Grant, Nov 17, 2004
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  3. You can try setting your gateway as the common NIC card IP for each machine
    and with the highest metric.
    For eg. on server B you can add a gateway like below
    route add <server A IP> mask <subnet mask> <common NIC IP on server A>
    metric 1
    This will force all traffic going to A only thru' this NIC unless it is
    Janani V[MSFT], Nov 17, 2004
  4. to > the LAN, the other directly to Server B. Ditto in Server B, except it
    That is always bad.
    It will always follow the routing table. It will always take the first route
    to the destination as it is listed in the routing table.

    The proper way to "mirror" the server is to run one nic in each machine and
    place them together on the same subnet. Then use Network Load Balancing
    (NLB), also known as "Server Clustering" to keep them in sync and provide
    fault tolerance.

    Even if you don't use NLB, you should still run one NIC in each machine.

    Here are some issues with multi-homing. They don't all apply to you, but it
    is good to know about them just the same.

    175767 - Expected Behavior of Multiple Adapters on Same Network;EN-US;175767

    157025 - Default Gateway Configuration for Multihomed Computers;en-us;157025&Product=win2000

    272294 - Active Directory Communication Fails on Multihomed Domain

    191611 - Symptoms of Multihomed Browsers;EN-US;191611

    Microsoft Windows XP - Multihoming Considerations
    Phillip Windell, Nov 17, 2004
  5. Brian

    Brian Guest

    Why is this "bad"?

    Why is it better to use only one NIC? Surely, if I wish to cut down on
    network traffic and direct specific traffic to a particular machine, without
    causing network congestion, multiple NICs are better.
    Brian, Nov 19, 2004
  6. No it doesn't. You put three Nics in a machine and the network simply sees
    it as three separate and distinct machines, it does *not* see it a one
    machine with three Nic. that is what all those articles I gave you were
    about. The key article is this one, which was the first one I listed right
    at the top.

    175767 - Expected Behavior of Multiple Adapters on Same Network;EN-US;175767

    The proper way to cut down on excess traffic or bottle necks it to properly
    segment you LAN into subnets with routers ("real" routers, not Internet NAT
    Devices) to reduce broadcasts. Beyond that you would just use a fast Nic at
    the Server and the Switch port it plugs into, such as replacing the 100 Nic
    with a Gig Nic and using a Gig Module in the Switch,...the cable between
    them may need upgraded as well (minimum CAT5E).

    "Nic Teaming" is a third party solution that came along later "after the
    fact". These are special Nics that come with special software of their own
    to make them work together. This is not a "Windows" solution.
    Phillip Windell, Nov 19, 2004
  7. Brian

    Brian Guest

    Errr, look, this appears to be becoming a circular argument.

    Basically I *_WANT_* the machine to appear as two seperate and distinct
    machines, so that each NIC can do a seperate and distinct job! I want one
    NIC to be the way most users access the server and I want the other NIC to be
    the way in which the other server accesses the first server.

    While it might be nice to be out in the world you inhabit where I could just
    whistle up another router or switch at the wave of a magic wand, I am working
    to a strictly limited budget here, trying to make do with what I bloody well
    have on hand. Now, if windows cannot do this, why not admit it, instead of
    trying to tell me that this is a "bad idea" and provide no reasons? If its a
    limitation of Windows, so be it but it appears to me to work under Unix
    'cause I've actually done it there.
    Brian, Nov 21, 2004
  8. Brian

    Bill Grant Guest

    Don't get excited. The reason two NICs cause problems relates to computer
    names. In most cases, machines are addressed by name, not by IP address.
    When a machine has more than one network interface, naming systems become
    confused. This causes problems in MS systems with the computer browser
    service and WINS, but it can have similar problems with DNS names.

    Your real problem is this. How do you ensure that your machine uses one
    NIC for one particular purpose but the other for some other purpose? How
    does the software decide which NIC to use?
    Bill Grant, Nov 21, 2004
  9. Brian

    Brian Guest

    Through ip address. If we utilise IP numbers instead of names, it doesn't
    matter what each NIC is known as in the DNS. However, it appears that this
    is not possible.

    Look, increasingly it looks like this is impossible. As to why, I'm not
    sure 'cause as I've said I've done this relatively easily in Unix, using NFS.
    I've tried installing unix services for windows but it appears they've made
    a butchery of that, as well as nfs doesn't work all that well. Perhaps I
    should just recommend to the boss that we rip this abortion out and put in a
    real os that works?
    Brian, Nov 21, 2004
  10. Brian

    Bill Grant Guest

    If you are not prepared to take a rational look at the problem, that is
    probably the best way for you to go.
    Bill Grant, Nov 22, 2004
  11. It isn't circular. I am not sying that it sees the thing as two different
    machines *perfectly*. At Layer3 it sees it as two machines, but when you
    get into the machine name issues it is the same name, you end up with a
    conflict, the articles I gave you described.
    I have to get permission to buy pencils,....the sharpener is extra...
    Well, if you notice our "call letters",...I think we tried that phrase once,
    but I think it was too "corny" and they dropped it.
    Phillip Windell, Nov 22, 2004
  12. Brian

    Brad Bazley Guest

    I agree with the others, not the best way to segment traffic - but when your
    hands are tied for money, it may be the only way.

    I once did an NLB Cluster that needed to segment traffic in much the same
    way as what you're trying to do now: we had a NIC on the subnet that the
    NLB Cluster was listening, and NIC connected to a Crossover running between
    the two NLB Nodes as a Backchannel (NLB in Unicast mode with one NIC can't
    talk directly from one node to another unless you have a Backchannel)

    Basically, we gave the NIC's on the Crossover a Private Address (not
    remotely similar to the Addresses on the NLB NIC's) and changed the Binding
    Order in Network Connections > Advanced Settings. After this, we were able
    to successfully connect via IP Address without issue.

    I know it's probably frowned upon by the experts, but it

    Brad Bazley, Nov 23, 2004
  13. Brian

    Brian Guest

    I apologise. I wrote out of frustration. Is there a solution to this
    problem or should I simply give up and inform the boss this isn't possible
    under Windows?
    Brian, Nov 23, 2004
  14. Brian

    Brian Guest

    So, why isn't it then possible to assign different names under the DNS to
    the different IP numbers?

    I know it isn't possible, I've tried. Windows' idea of a DNS simply keep
    reassigning the ip numbers to the original names, without asking me to allow
    So, the why suggest I should just pop out and buy another router?
    Brian, Nov 23, 2004
  15. Brian

    Brian Guest

    Mmm, this doesn't appear to be possible any longer under Windows Server
    2003, unfortunately. I just tried to do it and the bindings window doesn't
    come up any more. :-|

    However, thats the effort. At least it was a constructive suggestion.
    Brian, Nov 23, 2004
  16. You can do that in DNS, but remember that DNS is only for FQDNs
    (machinename.domainname.tld), not Netbios Names. Netbios Naming is handled
    by WINS. You can makeup "fake" names in WINS and give them an IP# using a
    WINS Static entry.

    So you could create a fake name in WINS assign an IP# to it. Then when you
    want to copy the data you spoke of in earlier posts you would direct it to
    this "fake" name and it would follow the appropriate path.

    I did something a little similar. I won't use my real server names to
    protect the innocent but what I did was this. I have one machine called
    "server2" with a particular IP assigned. I then assigned a second IP# to
    the machine and bound it to a website running on that machine. In WINS I
    created a fake name called "Photography" and set it in WINS to the same IP
    as the second IP I had added to the Server2. Now when a user on the LAN
    opens their browser and enters http://photography it opens the site bound to
    that address, yet the Server2 itself nor IIS has any knowledge of the name
    "photography" because that exist only in the WINS database. Now mine was
    the same subnet so it followed the same wire, but if it had been a different
    subnet with a different Nic it would have followed the appropriate path.

    I suppose you could follow the same theory with DNS as long as you used a
    complete FQDN. You can probably also do this a HOST file (compares to DNS)
    or with an LMHOST file (compares to WINS).
    Phillip Windell, Nov 23, 2004
  17. Brian

    Brad Bazley Guest

    Hey Mate,

    Definitely possible - the scenario I described was under W2K3!

    Go to Network Connections > Click the Advanced Menu > Click Advanced
    Settings and your Binding Order is there.

    Brad Bazley, Nov 23, 2004
  18. Brian

    Brian Guest

    OK. I can see the bindings - if I highlight the NIC designated as being
    "mirror" I get in the lower pane, "File and Print Sharing for Microsoft
    Network" -> Internet Protocol (TCP/IP), "Client for Microsoft Networks" ->
    Internet Protocol (TCP/IP). The up/down arrows beside that pane of the
    window are greyed out.

    So how do I change them?
    Brian, Nov 26, 2004
  19. Forget the lower pane. Just set the proper Interface to the "top" in the
    upper pane.
    Phillip Windell, Nov 29, 2004
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