Wednesday, April 25, 2007

Changing the IP address of your Production Exchange server

There are two basic scenarios involving to change the IP address of Production exchange servers.

You might have heard many times, how Exchange relays upon AD (Active Directory) and how AD is relaying on DNS within active directory 2000 and 2003 multi master replication model.

Exchange is DNS dependent and uses DNS intensively all the times to deliver the messages and do most of its task. (Routing mail, locating mail enabled objects etc)

As long as the A record is updated on the DNS server, pointing back to a right IP address for the Mail server and your clients are not having problem to resolve the new IP address corresponds to the name of the Exchange server, there should not be any major issues.

Make sure there is no HOST file on your network somewhere hidden where DNS gets bypassed for name resolution if HOST file exist with the old information.

Below is the default location for the hosts file on windows.


The Hosts file is a common way to resolve a host name to an IP address through a locally stored text file that contains IP-address-to-host-name mappings. On most UNIX-based computers, this file is /etc/hosts. On Windows-based computers, this file is the Hosts file


  • Stored in \NTROOT\System32\drivers\etc. Host file characteristics:
  • An entry may be any valid string of up to 256 characters.
  • Commonly used names should be near the top.
  • Duplicate names are ignored.
  • Each line corresponds to 1 IP address.


  • The following describes the attributes of the Hosts file for Windows
  • A single entry consists of an IP (IPv4 or IPv6) address and one or more host names.
  • The Hosts file is dynamically loaded into the DNS client resolver cache, which Windows Sockets applications use to resolve a host name to an
  • IP address on both local and remote subnets.
  • When you create entries in the Hosts file and save it, its contents are automatically loaded into the DNS client resolver cache.
  • The Hosts file contains a default entry for the host name local host.
  • The Hosts file can be edited with any text editor.
  • Each host name is limited to 255 characters.
  • Entries in the Hosts file for Windows–based computers are not case sensitive.

The advantage of using a Hosts file is that users can customize it for themselves. Each user can create whatever entries they want,

Including easy-to-remember nicknames for frequently accessed resources.

However, the individual maintenance required for the Hosts file does not scale well to storing large numbers of FQDN mappings or reflecting changes to IP addresses for servers and network resources. The solution for the large-scale storage and maintenance of FQDN mappings is DNS. The solution for the maintenance of FQDN mappings for changing IP addresses is DNS dynamic update.

Window Sockets applications use host names or IP addresses when specifying a destination.

Host names must be resolved to an IP address before communication with the destination can begin

The standard methods of host name resolution include checking the

  • Local host name,
  • Checking the local Hosts file,
  • And querying DNS servers.


Windows-based hosts also check the DNS client resolver cache, which contains the entries in the Hosts file.

Finally I am adding some terminology for all of us to Brash some of our knowledge

Domain Name System (DNS) – A hierarchical, distributed database that contains mappings of DNS domain names to various types of data, such as IP addresses. DNS enables the specification of computers and services by user-friendly names, and it also enables the discovery of other information stored in the database.

Host name – The name of a computer or device on a network. Users specify computers on the network by their host names. To find another computer, its host name must either appear in the Hosts file or be known by a DNS server. For most Windows-based computers, the host name and the computer name are the same.

Host name resolution – The process of resolving a host name to a destination IP address.


Hosts file – A local text file in the same format as the 4.3 BSD UNIX /etc/hosts file. This file maps host names to IP addresses, and it is stored in the systemroot\System32\Drivers\Etc folder.

NetBIOS name - A 16-byte name of a process using NetBIOS.


NetBIOS name cache – A dynamically maintained table that resides on a NetBIOS-enabled host and that store recently resolved NetBIOS names and their associated IPv4 addresses.

NetBIOS name resolution – The process of resolving a NetBIOS name to an IPv4 address.


NetBIOS name server (NBNS) – A server that stores NetBIOS name to IPv4 address mappings and resolves NetBIOS names for NetBIOS-enabled hosts. WINS is the Microsoft implementation of a NetBIOS name server.

Windows Internet Name Service (WINS) – The Microsoft implementation of a NetBIOS name server.

WINS – See Windows Internet Name Service (WINS


IF the IP address needs to be change on Clustered Exchange servers you must update three items:

  • The cluster's IP address resources,
  • The IP addresses assigned to the virtual servers, and
  • The IP addresses assigned to the physical cluster nodes


Best Regards

Oz Ozugurlu

1 comment:

Anonymous said...

Hi Oz,

I have Exchange Server 2007 CCR mailbox cluster, I wonder if the mailbox server service can still be working in another node while I'm changing the passive IP address before failing it back ?

My goal here is to change the IP address on the production server node only while still maintaining the mailbox service to the user with the other recovery node.