Re: Multihomed server

From: Phillip Windell (_at_.)
Date: 02/04/05 

Date: Fri, 4 Feb 2005 10:48:15 -0600

"Mike Lowery" <selfspam@mouse-potato.com> wrote in message
news:u8V8$kiCFHA.2288@TK2MSFTNGP14.phx.gbl...
> These NICs aren't on the same subnet, they're on different networks. Both
> computers are on both networks. Windows knows this and its NetBIOS name
list
> shows two IPs for each computer. It seems to arbitrarily pick which IP
(or NIC)
> to use.

157025 - Default Gateway Configuration for Multihomed Computers
http://support.microsoft.com/default.aspx?scid=kb;en-us;157025&Product=win2000

272294 - Active Directory Communication Fails on Multihomed Domain
Controllers
http://support.microsoft.com/default.aspx?scid=kb;en-us;272294

191611 - Symptoms of Multihomed Browsers
http://support.microsoft.com/default.aspx?scid=kb;EN-US;191611

Microsoft Windows XP - Multihoming Considerations
http://www.microsoft.com/resources/documentation/windows/xp/all/reskit/en-us/prcc_tcp_qpzj.asp?

Multi-Homed machine can have only one Default Gateway. As far as I am
concerned it is simply an oversight in the design of GUI that allows you to
assign a Default Gateway to an interface when one other interface already
has one. At least with Server2003 it does warn you not to do this if you
attempt it, but it doesn't prevent you from doing it.

Inbound vs outbound are two different independent sessions and two
completely differnet instances of a "routing decision" being made. When the
software sends something out it simply dumps it on the TCP stack and leaves
it. The routing subsystem then decides what route to take based on the
destination and whatever route table entry correspondes to that. It is
perfectly normal (and expected) that a request for a resource can come in on
one interface and have the respose to the request go out a different
interface.

This is why any machine (server or not a server) should never be multihomed
unless it is the right reason for doing so and although I don't fully
understand why to did it, I suspect it is not the right reason. The proper
"good" reasons are when building a machine as a router or a NAT device.
Another reason is Nic-Teaming, but that requires special Nics. One other
reason would be to have a separate segment for a Tape Backup Device. 

-- 
Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com

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