Choosing a Topology

[This is pre-release documentation and subject to change in future releases. This topic's current status is: Milestone-Ready]

Topic Last Modified: 2010-07-16

When choosing a topology there are three supported topology options:

Single consolidated Edge using network address translation (NAT)
Scaled consolidated Edge using NAT and DNS load balancing
Scaled consolidated Edge using public IP and hardware load balancing

The following table summarizes the functionality available with the three supported Communications Server 2010 topologies. The column headings indicate the functionality available for a given Edge configuration option. Using the Scaled Edge (DNS LB) option as an example, you can see that it supports High Availability, requires network address translation of Edge external interfaces, does not support publicly routable IP addresses, reduces cost because a hardware load balancer is not required and does not support failover for Exchange UM, PIC, and federation with Office Communications Server 2007 R2 or Office Communications Server 2007.

Summary of Edge Server Topology Options

Topology	High Availability	NAT Allowed	Additional Public IP required	Cost	Failover for Exchange UM (remote user), PIC, and federation with Office Communications Server 2007 R2 or Office Communications Server 2007
Single Edge	No	Yes	No	Yes	No
Scaled Edge(DNS load balancer)	Yes	Yes	No	Yes	No
Scaled Edge(Hardware load balancer)	Yes	No	Yes	No	Yes

Note:
The NAT Allowed and Additional Public IP required columns pertain only to the Edge external interfaces. A Yes in the NAT Allowed column means that the associated Edge Server topology supports the use of network address translation on the Edge external interfaces. If you decide to use NAT, you must use it on all three external interfaces. A Yes in the Additional Public IP required column means that you will need extra public IP addresses to deploy the associated Edge Server topology.

Note:

The NAT Allowed and Additional Public IP required columns pertain only to the Edge external interfaces. A Yes in the NAT Allowed column means that the associated Edge Server topology supports the use of network address translation on the Edge external interfaces. If you decide to use NAT, you must use it on all three external interfaces. A Yes in the Additional Public IP required column means that you will need extra public IP addresses to deploy the associated Edge Server topology.

The primary decision points for Topology selection are high availability and load balancing. The requirement for high availability can influence the load balancing decision.

High Availability–If you need high availability, deploy at least two Edge servers in a pool. A single Edge pool will support up to ten Edge servers. If more capacity is required, you can deploy multiple Edge pools. As a general rule, 10% of a given user base will need external access.
DNS load balancing–DNS load balancing is the recommended approach for load balancing Communications Server 2010 Edge Servers when using NAT for the Edge external interfaces.

Note:

DNS load balancing combined with publicly routable IP addresses for Edge external interfaces is not supported.
Hardware load balancing–Hardware load balancing is supported for load balancing Communications Server 2010 Edge Servers when using publicly routable IP addresses for the Edge external interfaces. For example, you would use this approach in situations where failover is required for any of the following applications:
- PIC
- External access to Exchange 2007 UM or Exchange 2010 UM
- Federation with companies running Microsoft Office Communications Server 2007 or Microsoft Office Communications Server 2007 R2
These three applications will continue to operate but they are not DNS load balancing aware and will only connect to the first Edge server in the pool. If that server is unavailable, the connection will fail.