"dual homing" and having two network cards

[Advanced User]

What are the implications of having two network cards on
a server? Can I have the two connections on different
subnets or will I need to install routing protocols such
as OSPF or set up static routes?

What about having two network cards on the same subnet,
but one bound to the DNS server service and one bound to
the IIS6 server service?
Would I need to use Network Load Balancing on both cards
so that I can get automatic failover support?

If my clients connect to a fileserver over one network
link and IP address, and they get a response from another
IP address, what will the client do?

Any knowledgebase articles would be greatly appreciated.
We use Windows 2003 and Windows 2000, with XP clients.

 

[Giuseppe Pellegrino]

What are the implications of having two network cards on
a server? Can I have the two connections on different
subnets or will I need to install routing protocols such
as OSPF or set up static routes?

Yes, you can set up TCP/IP on the two cards differently, they can stay on
the same subnet or two different subnets.
RRAS with RIP or OSPF is required if you want IP traffic to be routed via
the server between the two network segments. If you don't configure Routing
and Remote Access both subnets can reach the server independently but you
won't be able to pass traffic from one subnet to another.

What about having two network cards on the same subnet,
but one bound to the DNS server service and one bound to
the IIS6 server service?

It is a good solution if you want to optimize network traffic and security.
You can for example bind IIS to one IP address and have anybody locate the
IIS service but not DNS or DHCP which you may want to bind to another
network card and IP address visible to internal users only. Each service
will respond only on the NIC you bind it to.

Would I need to use Network Load Balancing on both cards
so that I can get automatic failover support?

NLB refers to cluster configuration which, in a very simple way, is a group
of servers acting like one.

If my clients connect to a fileserver over one network
link and IP address, and they get a response from another
IP address, what will the client do?

Depends on how you call the file server:
1. By IP address. You reach the file server exclusively through the network
card holding that IP address. No mistake can be made.
2. By NetBIOS name (such as server01). This is usually a broadcast call,
NetBIOS/NETBEUI protocol is used. The file server can be reached only if the
call comes from the same network segment where the server resides. NetBIOS
can't pass though routers. In this case the network card responding first
will establish the connection, you can't tell which and you can't control
binding.
3. By hostname (such as server01.domain.com). The client locate the IP
address passed by its referring DNS server. You must configure a host record
on the DNS service to bind together a name with an IP address. You ask DNS
for the file server, DNS tells you the corresponding IP address, you
establish connection with that given IP address.
You can also map more IP addresses to a single hostname, but I wouldn't go
too far =)

Any knowledgebase articles would be greatly appreciated.

An entire book would be farirly enough!

We use Windows 2003 and Windows 2000, with XP clients.

Good choice!!

Greetings.

Giuseppe Pellegrino

 

[Danny Slye - [MSFT}]

Having two NICs on separate subnets is no problem. You can use static
routes or use a routing protocol.
Having two NICs on the same subnet is not recommended. See: 175767
Expected Behavior of Multiple Adapters on Same Network
http://support.microsoft.com/?id=175767
Network Load Balancing is not designed for this. It is designed to enable
multiple servers to share a single virtual IP address.
See: 240997 Configuring Network Load Balancing
http://support.microsoft.com/?id=240997
You can buy "teaming NICs" that perform load balancing and failover from
most of the major vendors
How clients respond to a response from a different IP than the send IP
depends on the client application. Many apps will reject the response.
Here's a few articles:
140859 TCP/IP Routing Basics for Windows NT
http://support.microsoft.com/?id=140859
120642 TCP/IP and NBT Configuration Parameters for Windows 2000 or Windows
NT
http://support.microsoft.com/?id=120642
254101 Network Adapter Teaming and Server Clustering
http://support.microsoft.com/?id=254101
321708 HOW TO: Use the Network Diagnostics Tool (Netdiag.exe) in Windows
2000
http://support.microsoft.com/?id=321708
323339 HOW TO: Enable TCP/IP Forwarding in Windows Server 2003
http://support.microsoft.com/?id=323339
230082 HOW TO: Enable TCP/IP Forwarding in Windows 2000
http://support.microsoft.com/?id=230082
300986 HOW TO: Diagnose and Test TCP/IP or NetBIOS Network Connections in
http://support.microsoft.com/?id=300986
266771 HOW TO: Change the Binding Order in Windows 2000
http://support.microsoft.com/?id=266771
102908 How to Troubleshoot TCP/IP Connectivity with Windows 2000 or Windows
NT
http://support.microsoft.com/?id=102908
169790 How to Troubleshoot Basic TCP/IP Problems
http://support.microsoft.com/?id=169790
224829 Description of Windows 2000 TCP Features
http://support.microsoft.com/?id=224829
157025 Default Gateway Configuration for Multihomed Computers
http://support.microsoft.com/?id=157025
298447 A List of Windows 2000 White Papers and Technical Resources
http://support.microsoft.com/?id=298447

--------------------

What are the implications of having two network cards on
a server? Can I have the two connections on different
subnets or will I need to install routing protocols such
as OSPF or set up static routes?

What about having two network cards on the same subnet,
but one bound to the DNS server service and one bound to
the IIS6 server service?
Would I need to use Network Load Balancing on both cards
so that I can get automatic failover support?

If my clients connect to a fileserver over one network
link and IP address, and they get a response from another
IP address, what will the client do?

Any knowledgebase articles would be greatly appreciated.
We use Windows 2003 and Windows 2000, with XP clients.

Danny Slye
Microsoft Technical Support
This posting is provided "AS IS" with no warranties and confers no rights