Executive Summary:
When you're configuring a new Microsoft Windows server that has multiple network interface cards (NICs), it's important that you disable any NICs that aren't plugged in to the network. If you don't disable an unused NIC, problems can arise on domain controllers (DCs) running Domain Name System (DNS). The DNS server problems can impede the performance of client computers.
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When you're configuring a new
server that has multiple NICs, it's
important that you disable any NICs
that aren't plugged in to the network.
If you don't disable an unused NIC,
the Windows software will assign it an
IP address from the 169.254.x.x subnet. This address isn't used anywhere
on the network and isn't routable
across any WAN routers.
At this point you might be
thinking, "So if it isn't connected, what's the problem?" Problems can
arise on domain controllers (DCs)
running DNS. Servers register all
active IP addresses with the default
DNS server. On a DC, this has the
side effect of registering the server
in Active Directory (AD) as a DC
with two IP addresses: its valid IP
address and the invalid 169.254.x.x
address.
When a client makes a DNS
request to find all the DCs for the
appropriate domain, occasionally the
client will be given the invalid 169.254.x.x address as a valid DC address
because addresses are returned in a
round-robin fashion.
The client will then
attempt to contact the
DC using this invalid
address. Of course,
it won't be able to
contact the DC, and
the connection will fail. The client will
then attempt to look
up another DC using
DNS. Eventually the
client will succeed, and
all will be fine. However, all these extra
lookups will slow down
the client computer.
We learned about
this problem while
attempting to connect
a new storage appliance. The appliance
was able to register
with the domain but
periodically would be
unavailable when we
attempted to browse for files located
on the appliance. We had to manually
go through DNS and remove all of
the invalid entries and reregister the
appliance with the domain to correct
the problem.
So, the moral of the story is this:
If you have multiple NICs in a server,
disable those NICs that aren't being
used.
—Chris Lamb, Director,
IT Infrastructure, HIT Entertainment
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Then I checked our DNS registrations. It shows three 169 addresses. While not too bad for a 15,000 person organizaion, it's still three more then should be there. All three have "(same as parent folder)" for their hostname. Is there a way to track which machines these are coming from?
Mahoney August 30, 2007 (Article Rating: