Can you have 2 NICs connected to internet at the same time?

Hi all,

We're changing ISPs and would like to have some servers operate on both
networks at the same time. The servers have 2 NIC cards and I was
planning to put the second card on the new network.

This seems to work at first when experimenting inside our network,
however it turns out that the machines are not accessible from the
Internet on their secondary network cards despite the fact that we can
access them fine here from another computer plugged into the same switch.

Is it not possible to have a machine operate on two different Internet
IP ranges at the same time? I know you can only have one default
gateway and perhaps this is the problem.

Is there any other way we can somehow get the machine to appear to be on
both networks concurrently while we migrate domain names and services to
the new IP address? If not, we're going to have to physically duplicate
all the services using spare computers which will be extremely time
consuming.

Are there any other ways around this problem?

Thanks,

Nick...

Yes, only one default gateway on one computer. However, the following link may help.

RoutingOne router goes to the corporation email server and another one goes to the Internet. Symptoms: you have one router connecting to the corporation for email ...
www.chicagotech.net/routing.htm



Bob Lin, MS-MVP, MCSE & CNE
Networking, Internet, Routing, VPN Troubleshooting on http://www.ChicagoTech.net
How to Setup Windows, Network, VPN & Remote Access on http://www.HowToNetworking.com
"Nick Gilbert" <(E-Mail Removed)> wrote in message news:(E-Mail Removed)...
Hi all,

We're changing ISPs and would like to have some servers operate on both
networks at the same time. The servers have 2 NIC cards and I was
planning to put the second card on the new network.

This seems to work at first when experimenting inside our network,
however it turns out that the machines are not accessible from the
Internet on their secondary network cards despite the fact that we can
access them fine here from another computer plugged into the same switch.

Is it not possible to have a machine operate on two different Internet
IP ranges at the same time? I know you can only have one default
gateway and perhaps this is the problem.

Is there any other way we can somehow get the machine to appear to be on
both networks concurrently while we migrate domain names and services to
the new IP address? If not, we're going to have to physically duplicate
all the services using spare computers which will be extremely time
consuming.

Are there any other ways around this problem?

Thanks,

Nick...

I think the whole premise is flawed. There is no big long trasition period
to transit from one ISP to another to cause you to even need such a solution
in the first place.

Get the second connection going and established with the new ISP.

Have the authoritative DNS for your Domain Names changed to the DNS of the
new ISP (assuming the old ISP was the authoritative DNS to start with).

Have the old ISP (if they are willing) to change the IP#s of the Domain
Names to the new IP#s,..this will cover the transition period so that no
matter which ISP's DNS is queried you will still get the correct IP#. They
should be willing to do that,..it is no different than if you had a web site
with a Hosting company that was not your ISP.

Once the Internet Root Servers are aware of the authoritative DNS change
you're all done, and you can have the old ISP remove any DNS entries for
your Names.

--
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.
-----------------------------------------------------

"Nick Gilbert" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Hi all,
>
> We're changing ISPs and would like to have some servers operate on both
> networks at the same time. The servers have 2 NIC cards and I was planning
> to put the second card on the new network.
>
> This seems to work at first when experimenting inside our network, however
> it turns out that the machines are not accessible from the Internet on
> their secondary network cards despite the fact that we can access them
> fine here from another computer plugged into the same switch.
>
> Is it not possible to have a machine operate on two different Internet IP
> ranges at the same time? I know you can only have one default gateway and
> perhaps this is the problem.
>
> Is there any other way we can somehow get the machine to appear to be on
> both networks concurrently while we migrate domain names and services to
> the new IP address? If not, we're going to have to physically duplicate
> all the services using spare computers which will be extremely time
> consuming.
>
> Are there any other ways around this problem?
>
> Thanks,
>
> Nick...

Sorry but this solution is not practical for us. The machines in are DNS
servers themselves have to be globally registered. Additionally, the
machines host many websites for which we don't control the domain names.
It will take several days to change everything over.

As this it isn't possible to have two NICs in one machine, I will have
to mirror the DNS and websites on a new machine on the new network or
use a dual WAN port router to join the networks together.

Nick...


Phillip Windell wrote:
> I think the whole premise is flawed. There is no big long trasition period
> to transit from one ISP to another to cause you to even need such a solution
> in the first place.
>
> Get the second connection going and established with the new ISP.
>
> Have the authoritative DNS for your Domain Names changed to the DNS of the
> new ISP (assuming the old ISP was the authoritative DNS to start with).
>
> Have the old ISP (if they are willing) to change the IP#s of the Domain
> Names to the new IP#s,..this will cover the transition period so that no
> matter which ISP's DNS is queried you will still get the correct IP#. They
> should be willing to do that,..it is no different than if you had a web site
> with a Hosting company that was not your ISP.
>
> Once the Internet Root Servers are aware of the authoritative DNS change
> you're all done, and you can have the old ISP remove any DNS entries for
> your Names.
>

"Nick Gilbert" <(E-Mail Removed)> wrote in message
news:etQl$(E-Mail Removed)...
> Sorry but this solution is not practical for us. The machines in are DNS
> servers themselves have to be globally registered. Additionally, the
> machines host many websites for which we don't control the domain names.
> It will take several days to change everything over.
>
> As this it isn't possible to have two NICs in one machine, I will have to
> mirror the DNS and websites on a new machine on the new network or use a
> dual WAN port router to join the networks together.

Maybe I misunderstood all that you were doing,...maybe I still do,...let's
try again.

You can run two Nics in the machines with each one configured properly for
the particular ISP connected to that nic. It should respond to traffic from
either Nic just fine. What it will not do is have traffic that is initiated
from the machine itself (meaning that machine is acting as the Source) use
the old ISPs nic. All outbound traffic will use the Nic that has the Default
Gateway,...and you can have only one Default Gateway. Static Routes in the
Routing Table can force the use of a particular nic for a particular
Destiantion, but I don't think that applies to this situation.

In the meantime it doesn't matter who is going to handle the DNS in the
future. You need functioning connectivity to the Resources via the new ISP.
Whoever is currently hosting the DNS Records needs to adjust the Host
Records or CNAME Records to point to the new IP#s. Have whoever is the
current Authority for the Names change the Authoritative DNS to the new DNS
server. At the same time create the proper records on the new DNS Server
(whoever is hosting them). Give the Root Servers a few days to adjust to
the change in DNS authority, then the original old DNS Servers can have the
records deleted.


--
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.
-----------------------------------------------------

"Phillip Windell" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Whoever is currently hosting the DNS Records needs to adjust the Host
> Records or CNAME Records to point to the new IP#s.

Little correction.
CNAMEs don't point to IP#s, they point to A (Host) Records, so only the A
Records need the IP# changed.

--
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.
-----------------------------------------------------

> You can run two Nics in the machines with each one configured properly for
> the particular ISP connected to that nic. It should respond to traffic from
> either Nic just fine.

Well in practice this doesn't seem to work. The machine always seems to
respond via the default gateway rather than via the NIC that originally
received the request.

Searching around the net, it appears that other operating systems can
handle this scenario, but Windows can't. Apparently you can only use
multiple NICs if they are on mutually exclusive networks (ie, one or
more private LANs which each have different subnets and/or ONE
connection to the Internet).

Nick...

"Nick Gilbert" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
>> You can run two Nics in the machines with each one configured properly
>> for the particular ISP connected to that nic. It should respond to
>> traffic from either Nic just fine.
>
> Well in practice this doesn't seem to work. The machine always seems to
> respond via the default gateway rather than via the NIC that originally
> received the request.

That is just what I said it would do. Anything leaving the machine will
follow the Default Gateway.

> Searching around the net, it appears that other operating systems can
> handle this scenario, but Windows can't. Apparently you can only use
> multiple NICs if they are on mutually exclusive networks (ie, one or more
> private LANs which each have different subnets and/or ONE connection to
> the Internet).

Nics must be on different subnet unless they are Teamed.
Multiple IP#s from the same subnet must go on the same Nic as alternate
IP#s.

--
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.
-----------------------------------------------------