exchange 2013 coexistence environment and the exchange legacy infrastructure | 8#23

of 21 | Part 08#23 | Exchange 2013 coexistence environment and the Exchange

legacy infrastructure

Written by Eyal Doron | o365info.com | Copyright © 2012-2015

EXCHANGE 2013 COEXISTENCE

ENVIRONMENT AND THE EXCHANGE LEGACY

INFRASTRUCTURE | 8#23

In this article, I would like to focus on the term “legacy” that is used very often in the

Exchange 2013 coexistence environment. As usual, the common assumption is that

everyone knows and understands this term, but in reality, the term is not so clear,

and we are as ashamed to admit that we don’t fully understand the meaning of the

term.

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In the context of Exchange 2013 coexistence environment, the term: “Legacy” can

be translated into a couple of options:

Legacy Exchange client

Legacy Exchange infrastructure

Legacy namespace

Using the term legacy – not a politically-

correct term

In my opinion, the term “legacy” seems always a little out of place.

What is the meaning of legacy?

Does it mean that, up until now, the existing Exchange infrastructure that was

sworn to “serve and protect” is useless or, not good anymore?

Does it mean that only the “new Exchange infrastructure” is meaningful and

important?





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I know it’s philosophizing but, I think that the “Exchange guys”, should choose a

more politically-correct term because, the association that appears in mind when I

hear the term “legacy” is something like this:

Regardless of my reservations, as a loyal citizen of the Exchange nation, I will

continue to use this term as long as it needed.





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How to introduce Exchange CAS 2013 to

existing Exchange environment

Let’s make it simple. When a new Exchange server version is released, and we want

to “adapt” this new Exchange server version we have two basic options:

Option 1: “Wipe out” the existing Exchange infrastructure and “plant” the new

Exchange server version or in more technical words: install the new Exchange

server version and decommission the former Exchange server version.

Option 2: Implement an Exchange infrastructure that can be described as: “side by

side” which mean: add the new Exchange server version (Exchange 2013 server, in

our case) to the existing Exchange environment and, slowly start to “migrate” all the

resources such as user mailboxes and Exchange web services to the “new Exchange

infrastructure”.





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Only after there is no Exchange client that relies on\use the former Exchange

infrastructure, we can start to decommission the “older Exchange environment”.

“Old” Exchange infrastructure | Terms used

When implementing a project of Exchange coexistence, the Exchange 2013

infrastructure is the “new infrastructure” and all the rest of the former Exchange

server versions can be described as:

Older version of Exchange

Former versions of Exchange

Legacy Exchange infrastructure

In the following diagram, we can see that from the Exchange 2013 point of view,

Exchange 2010 infrastructure and Exchange 2007 infrastructure consider as: Legacy

Exchange infrastructure.





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Legacy Exchange clients

The term “legacy Exchange client” relates to Exchange client that their mailbox is

hosted on the legacy Exchange mailbox server.

In our scenario of Exchange 2013 coexistence environment, each Exchange user

who is a mailbox is hosted on Exchange 2007 Mailbox server or Exchange 2010

Mailbox server consider as “legacy Exchange client”.





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Throughout the series of articles, I will not use the term: “legacy Exchange client”

but instead, I will refer to “non-Exchange CAS 2013 server client” as: Exchange 2007

clients or Exchange 2010 clients.

In an Exchange 2013 coexistence environment, “legacy Exchange clients” such as

Exchange 2007/2010 clients will need to Initialize the communication process with

the Exchange 2013 CAS server, and the “rest” of the process will be “determined” by

the Exchange 2013 CAS.

Exchange CAS 2013 will decide how to continue the client protocol connectivity flow

based the specific scenario parameters such as the Exchange client version, the

Exchange client physical location and so on.

For example, the Exchange CAS 2013 can decide to Proxy the legacy Exchange client

request to the legacy Exchange infrastructure by himself or send to the legacy

Exchange client a redirection command, etc.





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How the Exchange CAS 2013 server does treat

his legacy clients?

Q1: “Why does the Exchange 2013 server need to deal with legacy Exchange clients?

Why not implementing an architecture, in which Exchange 2013 will serve only

Exchange 2013 client, and the “other legacy Exchange servers” will serve their

legacy Exchange clients?





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A1: Well, the simplified answer is that in an Exchange 2013 coexistence

environment, the most updated Exchange server version (Exchange 2013 CAS in

our scenario) will need to be configured as the “focal point” for all the Exchange

clients, including native Exchange 2013 “native clients” + legacy Exchange clients

(Exchange 2007/2010 clients).

Note – You can read more information about the concept of Exchange CAS 2013

server as a focal point in the article – Exchange Public infrastructure | Public versus

non Public facing Exchange site

The Exchange 2013 CAS is “smart enough” to recognize Exchange client version

such as Exchange legacy client and decide about the “next step” such as: Proxy the

Exchange legacy client requites to the “right Exchange legacy infrastructure”

For example, when Exchange 2007 Outlook client (Exchange user who is a mailbox

is hosted on Exchange 2010 Mailbox server) address Exchange CAS 2013 server, the

Exchange CAS 2013 server “understand” that the specific client “belong” to the





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Exchange 2010 infrastructure and for this reason, the Exchange CAS 2013 server

will proxy the request to available Exchange 2007 CAS.

Note – from the Exchange 2007 client point of view, this process is transparent. The

meaning is that the Exchange 2007 client is not where to the fact that his request

was “routed” to the Exchange 2007 CAS.

From the Exchange 2007 client point of view, the Exchange CAS 2013 server is the

element that provides the required mailbox data.

The reason for using Legacy namespace in

Exchange 2013/2007 coexistence environment

Let’s start from the end: the term “Exchange legacy namespace”, is relevant only in

a scenario of Exchange 2013/2007 coexistence environment.

The use of the “Exchange legacy namespace”, will be implemented for Exchange

2007 OWA clients and Exchange 2007 Outlook clients that access the Exchange

2007 web services.








Exchange 2007 clients and request for access mailbox content

In Exchange 2013/2007 coexistence environment, Exchange 2013 CAS behaves

differently with different Exchange 2007 client type.

In a scenario of Exchange 2007 Outlook and ActiveSync client that request access

to their mailbox content, Exchange CAS 2013 will proxy connection request to the

Exchange CAS 2007.

In a scenario in which the Exchange 2007 client is OWA client, Exchange CAS 2013

will not use the Proxy method, but instead, redirect the Exchange 2007 OWA

client to the Exchange CAS 2007 by using the Exchange CAS 2007 legacy

namespace.

This is one of the two reasons behind the need to create and use the legacy

namespace in Exchange 2013/2007 coexistence environment.





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Exchange CAS 2013 server, doesn’t know how to proxy, Exchange 2007 OWA client

requests to Exchange 2007 CAS server.

Generally speaking, Exchange CAS 2013 server prefers to implement the proxy

method because the Proxy method makes the Exchange client life simple. The

Exchange client doesn’t need to be familiar with the complex infrastructure of the

client protocol connectivity flow or play an “active role” in the communication

process. When implementing the method of Proxy, Exchange CAS 2013 does all the

“hard work,” work” and the Exchange client just enjoys from the ability to access his

mailbox data.

Because the Exchange CAS 2013 server doesn’t know how to proxy, Exchange 2007

OWA clients’ request, Exchange 2013 CAS uses a method which described as:

redirect or if we want to be more specific: silent redirect + SSO.





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Note – You can read more information about silent redirect + SSO in the article

– OWA client protocol connectivity flow in Exchange 2013/2007 coexistence

environment | 3/4

The redirection method is implemented by sending the Exchange client a URL

address of “other Exchange CAS servers” that can help the Exchange client.

In a scenario of Exchange 2007 OWA mail client, the Exchange CAS 2013 server will

send the client the URL address of existing Exchange 2007 CAS server.





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To be able to “refer” the Exchange 2007 OWA client to the Exchange CAS 2010, the

Exchange CAS 2013 “send” the Exchange 2007 OWA client browser a redirection

command with the URL address of the “destination Exchange CAS 2017” that

include the Exchange CAS 2007 legacy namespace.

The term: legacy namespace, describe the namespace that is assigned or “attached”

to the Exchange 2007 CAS server. For example: legacy.mail.o365info.com

In other words, to be able to refer to other or additional Exchange CAS servers (the

Exchange CAS 2007) we will need to use a different namespace form the primary

namespace. This is the reason or the need for using the: “legacy namespace”.

Exchange 2007 Exchange web services clients

The second reason for using the legacy namespace in Exchange 2013/2007

coexistence environment is the subject of: providing Exchange web services to

Exchange 2007 clients.

In Exchange 2013/2007 coexistence environment, Exchange 2007 client will need to

get their Exchange web services from Exchange 2007 CAS and not from Exchange

2013 CAS.

The reason is Exchange 2013 CAS doesn’t know how to provide Exchange web

services to the Exchange 2007 clients.

In the following diagram, we can see the concept of “redirecting Exchange 2007

clients” requests for Exchange web services to the – Exchange 2007 CAS.

In reality, there is no “real redirection process.

The Autodiscover information that Exchange 2013 CAS provides to the Exchange

2007 clients, includes the URL address and the FQDN that represents the legacy

namespace of the Exchange 2007 CAS such as: legacy.mail.o365info.com

When Exchange 2007 client looks at the host who can provide him Exchange web

services, Exchange 2007 client will use the URL address which includes the “referral”

to the Exchange CAS 2007.








Legacy names space – The concept of a

unique\dedicated namespace

In Exchange 2013/2007 coexistence environment, Exchange CAS 2013 need to

1. Redirect To Exchange 2007 OWA clients to the Exchange CAS 2007 server.

2. “Inform” Exchange 2007 client that the Exchange web service will be provided by

the Exchange CAS 2007 server.

To be able to “refer” to the Exchange CAS 2007, we will need to use a

unique\dedicated namespace for the Exchange CAS 2007 infrastructure, which is

different from the primary namespace.





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The “additional namespace” that will be assigned to the Exchange CAS 2007 server

described as: “legacy” because as we mention, Exchange relates to former versions

of Exchange server as: legacy.

The legacy namespace is based on a concept in which we continue to use the

existing domain name and add or use a different host name (prefix).

For example: in our scenario, the domain name is: o365info.com

The primary namespace that is used for publishing and addressing the Exchange

CAS 2013 is: mail.o365info.com

To be able to differentiate the Exchange CAS 2007 from the “primary namespace”,

we can use a naming convention such as: legacy.mail.o365info.com or another

option is to add to host name: “legacy” to the existing primary namespace. For

example: legacy.mail.o365info.com





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Technically speaking, there is no mandatory need for using the host name: legacy.

The legacy is not a reserve host name but instead, just a common naming

convention.

For example: we can use the following namespace: unclesam.mail.o365info.com as

the legacy namespace for Exchange CAS 2007 server.

It’s important to mention that will need to “publish” and update the “new legacy

namespace” is different infrastructures.

Recap





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We can use the following diagram as a “recap” for what we have to learn up until

now.

The concept of Exchange legacy namespace is relevant only in an Exchange

2013/2007 coexistence environment.

The “clients” that will be used the legacy namespace are: Exchange 2007 OWA

clients + Exchange 2007 clients such as Outlook that use the Exchange 2007 as a

source server for Exchange web service.

Exchange CAS 2013 uses the legacy namespace for implementing the process of:

“silent redirection” in which send a redirection command to the Exchange 2007

client browser using the legacy Exchange CAS 2007 namespace.

Exchange CAS 2013 uses the legacy namespace as part of the Autodiscover

information that he provides to Exchange 2007 clients. The Exchange 2007 client

will use the URL address that includes the Exchange 2007 legacy namespace for

addressing Exchange CAS 2007 when they need Exchange web services.





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The concept of two Public facing Exchange

CAS server in a single Exchange site

At first look, the concept of: “two Public facing Exchange CAS server in a single

Exchange site” seems a little odd. The standard convention of Exchange public

infrastructure in a scenario of: a Public facing Exchange site, is implemented most

of the time, by using a specific Exchange CAS server who serves as the

“representative” of a Public facing Exchange site.

Even in a scenario in which we implement a fault tolerance and load balancing

mechanism and use an array of Exchange CAS servers, the external client “see” only

one entity or one namespace such as: mail.o365info.com

In a scenario of Exchange 2013/2007 coexistence environment, we need to

implement a configuration, in which we need to use: two Public faces Exchange CAS

servers at the same time.

Exchange CAS 2013 which will be the “main Public facing Exchange CAS server” and

additionally, an Exchange CAS 2007 which will also have to have a public availability.

The “Exchange 2007 Public facing server” will serve Exchange 2007 OWA clients.





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The scenario in which external Exchange 2007 clients, will address the Public facing

Exchange 2007 CAS server are as follows:

1. External Exchange 2007 OWA clients

Exchange 2007 OWA clients will address the “primary” or the “main” Public facing

Exchange CAS server meaning – the Exchange CAS 2013. When the Exchange CAS

2013 recognizes that the external client is: Exchange 2007 OWA client, the Exchange

CAS 2013 will start a process of silent redirection in which he redirects the

Exchange 2007 OWA client browser, to the “Exchange 2007 Public facing server”.

For example:

Exchange 2007 OWA client addresses the Public facing Exchange 2013 CAS server

by using the URL address: mail.o365info.com

The redirection command that will “refer” the Exchange 2007 client, to the

Exchange 2007 Public facing server is based on a URL address that includes the

legacy namespace of the Public facing Exchange 2007 server. For example, the URL

address could be: https://legacy.mail.o365info.com/owa

The Exchange 2007 OWA client, will need to

Find the public IP address of the host: legacy.mail.o365info.com

Need to create a new HTTPS session with the “new destination host” the Public

facing Exchange 2007 server.

In simple words, to be able to enable this “flow”, we will need to “expose” also the

Exchange 2007 CAS and configure the Exchange 2007 server as a Public facing

Exchange CAS server.

2. External Exchange 2007 Outlook clients

Exchange 2007 Outlook clients will address the “primary” or the “main” Public facing

Exchange CAS server as the Autodiscover Endpoint. When the Exchange CAS 2013

recognizes that the external client is: Exchange 2007 Outlook client, the Exchange

CAS 2013 will create a “custom Autodiscover answer”, which includes the URL

address of the “Exchange 2007 Public facing server”.








When Exchange 2007 Outlook clients need a specific web service, the client will

address the Public facing Exchange 2007 CAS server using the legacy namespace.

The Exchange 2013 coexistence article series index page





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http://o365info.com/exchange-2013-coexistence-environment-and-client-protocol-connectivity-flow-the-prefix

exchange 2013 coexistence environment and the exchange legacy infrastructure | 8#23

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