Re: MultiHomed Workstation - Which NIC is being used?

Tech-Archive recommends: Repair Windows Errors & Optimize Windows Performance

From: RDK (RDK_News_at_NoSpamHotMail.com)
Date: 01/12/05

  • Next message: Herb Martin: "Re: Prevent Auto Modem Connection" 
    Date: Wed, 12 Jan 2005 17:01:22 -0500

    Steve.....Thanks this answers almost all of my questions. However,
    recalling my PS and your #4 below:

         4. All other traffic will leave the adapter that's highest bound.

        ps...I assume that any incoming traffic to my workstation webs and/or
    databases from devices (servers and/or users) on any of the
        three subnets will always return via the NIC on which it was
    received?...

    Let's assume that NIC1 is the "highest bound", does this mean that traffic
    from the 10.0.1.* subnet (coming in via NIC2) to a web server on my
    workstation from an Internet source (firewall DMZ for example) will exit
    back to the Internet via NIC1, or will it know that it has to exit via NIC2?

    Thanks......RDK

    "Steve Riley [MSFT]" <steriley@microsoft.com> wrote in message
    news:46779632411208050874498@news.microsoft.com...
    > OK. So you have three NICs, each in its own subnet, and each with a
    > default gateway configured. If you haven't changed any default settings,
    > these will all have the same metric. Therefore, routing will behave this
    > way.
    >
    > 1. Any traffic destined for subnet 10.0.0.0/24 will go out NIC1.
    >
    > 2. Any traffic destined for subnet 10.0.1.0/24 will go out NIC2.
    >
    > 3. Any traffic destined for subnet 10.0.2.0/24 will go out NIC3.
    >
    > 4. All other traffic will leave the adapter that's highest bound. Open the
    > Network Connections folder, choose Advanced from the menu, choose Advanced
    > Settings. Look at the Connections box on the Adapters and Bindings tab.
    > Whichever interface is listed first is the one that gets used. Windows
    > will never initiate oubound connections using the other two.
    >
    > Default gateways are used only when the destination address of a packet is
    > on some network other than the local segment, as defined by the subnet
    > mask. Thus, for the first three conditions, no default gateways are used
    > at all. In the fourth condition, the highest-bound NIC will process all
    > traffic. This will include any other subnets inside your internal network
    > as well as the Internet at large.
    >
    > Now say you have another subnet in your network, 10.0.3.0/24, and you
    > would like all traffic to that subnet to use NIC2. So long as there is
    > connectivity between 10.0.1.0/24 to 10.0.3.0/24, you can add this static
    > route:
    >
    > route add 10.0.3.0 mask 255.255.255.0 10.0.1.1
    >
    > Make sure that 10.0.3.0/24 knows how to route back through 10.0.1.0/24 for
    > any traffic that it receives from that subnet.
    >
    > Oh, and Shalom B. -- no, there is no facility in the stack to do any load
    > balancing of multiple NICs and default gateways.
    >
    >
    > Steve Riley
    > steriley@microsoft.com
    >
    >
    >
    >> Steve....255.255.255.0 is the subnet mask. Thanks...Rob
    >> "Steve Riley [MSFT]" <steriley@microsoft.com> wrote in message
    >> news:46162632410783153518016@news.microsoft.com...
    >>> Before I can fully answer, I need to know one thing: what is the
    >>> subnet mask on these interfaces?
    >>>
    >>> Steve Riley
    >>> steriley@microsoft.com
    >>>> Steve...Thanks for the information, except now I'm a bit confused by
    >>>> the reference article you sent me to. May I elaborate on my setup:
    >>>>
    >>>> NIC1 10.0.0.5 has a gateway (firewall router address) of 10.0.0.1
    >>>> and
    >>>> its "modem" is connected to ISP1 - 5 MBS
    >>>> NIC2 10.0.1.5 has a gateway (firewall router address) of 10.0.1.1
    >>>> and
    >>>> its "modem" is connected to ISP2 - 1 MBS
    >>>> NIC3 10.0.2.5 has a gateway (firewall router address) of 10.0.2.1
    >>>> and
    >>>> its "modem" is connected to ISP3 - 0.25 MBS
    >>>> except via my workstation these three subnets are not connected
    >>>> (well
    >>>> I guess they are connected via the Internet).
    >>>> In this mode if I fire up an app on my Win2k workstation which wants
    >>>> to access the interent, I'm never sure which NIC is actually
    >>>> servicing the request. In a development and production environment
    >>>> I prefer to keep the 5 MBS pipe clear for business traffic and use
    >>>> one of the others for testing. But, I do need to access devices on
    >>>> the 5 MBS subnet periodically. Now, my read of the reference
    >>>> article is that I should leave the gateway field blank for NIC's 1
    >>>> and 3, and to populate NIC2 with all three router addresses. Is
    >>>> this correct? And then I have to use the Router.exe to define
    >>>> routes for the other two??
    >>>>
    >>>> Networking is not my speciality, can you provide a couple concrete
    >>>> examples.
    >>>>
    >>>> Thanks....RDK
    >>>>
    >>>> ps...I assume that any incoming traffic to my workstation webs
    >>>> and/or databases from devices (servers and/or users) on any of the
    >>>> three subnets will always return via the NIC on which it was
    >>>> received?...
    >>>>
    >>>> "Steve Riley [MSFT]" <steriley@microsoft.com> wrote in message
    >>>> news:45224632410457423941917@news.microsoft.com...
    >>>>
    >>>>> The Windows IP stack supports only one default gateway. If all
    >>>>> three of your interfaces have routes out to the Internet, you will
    >>>>> be using only one interface. Which interface gets used depends on
    >>>>> how you've configured the stack.
    >>>>>
    >>>>> In no instance will you get any form of traffic load balancing. You
    >>>>> can configure varying metrics, but that usually makes sense only if
    >>>>> you're trying to make routing decisions based on cost. If you use a
    >>>>> lower (that is, more preferred) metric for faster connections then
    >>>>> *all* your traffic will go out that connection. If you use the same
    >>>>> metric everywhere, Windows XP and 2003 will use only one interface
    >>>>> for all traffic -- the one that's listed first in the binding order
    >>>>> in the advanced settings dialog. Windows 2000 just randomly picks
    >>>>> one.
    >>>>>
    >>>>> See http://support.microsoft.com/?id=157025 for some more details
    >>>>> on your configuration.
    >>>>>
    >>>>> It sounds like you're describing a need for "ISP load balancing."
    >>>>> Rainfinity makes a product called RainConnect that does exactly
    >>>>> that. Check it out.
    >>>>>
    >>>>> Steve Riley
    >>>>> steriley@microsoft.com
    >>>>>> You could do it 2 ways and still achieve the same result.
    >>>>>>
    >>>>>> In the Advanced properties of your network connections set a
    >>>>>> metric for each connection, a lower metric set to an interface
    >>>>>> makes that connection a preferred route for all outgoing traffic.
    >>>>>> Setting multiple interfaces with the same metric enables load
    >>>>>> sharing across these connections.
    >>>>>>
    >>>>>> If you are looking to set an application process (iexplore.exe in
    >>>>>> your case) to use a connection-of-choice for that process all the
    >>>>>> time, i don't think there is a way (but i am willing to be wrong
    >>>>>> about
    >>>>>> this).
    >>>>>> The next method used the Route.exe command line executable to set
    >>>>>> the metric for gateways using a default route which is persistent
    >>>>>> across system reboots.
    >>>>>> % Route Add 0.0.0.0 Mask 0.0.0.0 10.0.2.5 Metric 20 -p Let's say
    >>>>>> this was your 5MB connection
    >>>>>>
    >>>>>> % Route Add 0.0.0.0 Mask 0.0.0.0 10.0.1.5 Metric 22 -p and this
    >>>>>> was your 2MB connection
    >>>>>>
    >>>>>> % Route Add 0.0.0.0 Mask 0.0.0.0 10.0.0.5 Metric 35 -p and this
    >>>>>> was your 0.25MB connection
    >>>>>>
    >>>>>> RDK wrote:
    >>>>>>
    >>>>>>> ....I have a Windows 2000 workstation which has three NICs. Each
    >>>>>>> NIC (subnets 10.0.2.5, 10.0.1.5 and 10.0.0.5) has an independent
    >>>>>>> route to the internet. That is we have three redundant routes to
    >>>>>>> the internet (three different suppliers).
    >>>>>>>
    >>>>>>> One of these routes is low speed (250 KBS) while the others are
    >>>>>>> 1MB and 5MB.
    >>>>>>>
    >>>>>>> How can I tell which NIC is being used when I open up IE? Or,
    >>>>>>> how can I specify (without disabling the other NICs) which NIC
    >>>>>>> should be the primary (preferred) NIC, secondary, ... for
    >>>>>>> internet access?
    >>>>>>>
    >>>>>>> Thanks....RDK
    >>>>>>>
    >
    >

  • Next message: Herb Martin: "Re: Prevent Auto Modem Connection"

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