NetScaler Gateway
User groups utilizing NetScaler Gateway as their authentication point have additional access layer design decisions that must be considered. These design decisions are not applicable for non-
NetScaler Gateway authentication points.
Decision: Topology
Selection of the network topology is central to planning the remote access architecture to ensure that it can support the necessary functionality, performance and security. The design of the remote
access architecture should be completed in collaboration with the security team to ensure adherence to corporate security requirements. There are
two primary topologies to consider, each of which provides increasing levels of security:
• 1-Arm (normal security) - With a 1-arm topology, the NetScaler utilizes one physical or logical bonded interface, with associated VLAN and IP subnet, to transport both fronted traffic for users and backend traffic for the virtual desktop infrastructure servers and services.
• 2-Arm (high security) – With a 2-arm topology, the NetScaler Gateway utilizes two or more physically or logically bonded Transport of the frontend traffic for users is directed to one of these interfaces. The frontend traffic is isolated from backend traffic, between the virtual desktop infrastructure servers and services, which is directed to a second interface. This allows the use of separate demilitarized zones (DMZs) to isolate frontend and backend traffic flows along with granular firewall control and monitoring.
Decision: High Availability
If the NetScaler Gateway is unavailable, remote users will not be able to access the Citrix environment. Therefore at least two NetScaler Gateway servers should be deployed to prevent this
component from becoming a single point of failure.
When configuring NetScaler Gateway in a high availability pair, the secondary NetScaler Gateway monitors the first appliance by sending periodic messages, also called a heartbeat message or health check, to determine if the first appliance is accepting connections. If a health check fails, the secondary NetScaler Gateway tries the connection again for a specified amount of time until it determines that the primary appliance is not working. If the secondary appliance confirms the health check failure, the secondary NetScaler Gateway takes over for the primary NetScaler Gateway.
Each NetScaler Gateway appliance must be running the same version of the NetScaler Gateway software and have the same license. For additional considerations when configuring a NetScaler
Gateway high availability pair please reference Citrix eDocs – How High Availability Works.
Decision: Platform
In order to identify an appropriate NetScaler platform to meet project requirements, the key resource constraints must be identified. Since all remote access traffic will be secured using the secure sockets layer (SSL_, transported by Hypertext Transfer Protocol (HTTP) in the form of HTTPs, there are two resource metrics that should be targeted:
• SSL throughput – The SSL throughput is the gigabits of SSL traffic that may be processed per second (Gbps).
• SSL transaction per second (TPS) – The TPS metric identifies how many times per second an
Application Delivery Controller (ADC) may execute an SSL transaction. The capacity varies primarily by the key length required. TPS capacity is primarily a consideration during the negotiation phase when SSL is first setup and it is less of a factor in the bulk encryption / decryption phase, which is the majority of the session life. While TPS is an important metric to monitor, field experience has shown that SSL Throughput is the most significant factor in identifying the appropriate NetScaler Gateway.
For more information, please refer to the Citrix white paper – Best Practices for Implementing 2048-bit SSL.
The SSL bandwidth overhead average is often considered negligible relative to the volume of virtual desktop traffic and is not typically accounted for as part of required SSL Throughput. However making provisions for SSL bandwidth will help ensure the total throughput estimated is sufficient. The fixed bandwidth added to packet headers can vary according to the encryption algorithms used and the overall percentage of bandwidth may vary widely according to packet size. Ideally, the overhead should be measured during a proof of concept or pilot. However, in the absence of such
data incrementing the workload bandwidth by 2% is a reasonable rule of thumb. Therefore, to determine the SSL throughput required by a NetScaler platform, multiply the maximum concurrent
bandwidth for a datacenter by 1.02:
For example, assuming 128Mbps maximum concurrent bandwidth, the appropriate NetScaler model can be determined as follows:
The SSL throughput value should be compared to the throughput capabilities of various NetScaler platforms to determine the most appropriate one for the environment. There are three main platform
groups available, each of which provides broad scalability options.
• VPX – A NetScaler VPX device provides the same full functionality as hardware NetScaler. However, NetScaler VPXs can leverage ‘off the shelf’ servers for hosting and are suitable for small to medium sized environments.
• MDX – A NetScaler MDX is the hardware version of the NetScaler devices. The MDX device is more powerful than the virtual NetScaler and can support network optimizations for larger scale
enterprise deployments.
• SDX – A NetScaler SDX is a blend between the virtual and physical NetScaler devices. An SDX machine is a physical device capable of hosting multiple virtual NetScaler devices. This consolidation of devices aids with reducing required shelf space and device consolidation. NetScaler SDXs are suitable for handling network communications for large enterprise deployments.
SSL throughput capabilities of the
NetScaler platforms may be found in the Citrix NetScaler data sheet. Therefore, based on the example calculation above, a NetScaler MPX 5500 appliance would be sufficient to handle the required load. However, actually scalability will depend on security requirements. NetScaler SSL throughput decreases with the use of increasingly complex encryption algorithms and longer key lengths. Also, this calculation represents a single primary NetScaler. At a minimum, N+1 redundancy is recommended which would call for an additional NetScaler of the identical platform and model.
Note: The Citrix NetScaler data sheet typically represents throughput capabilities under optimal conditions for performance. However, performance is directly affected by security requirements. For example, if the RC4 encryption algorithm and a 1k key length are used, a VPX platform may be able to handle more than 500 HDX proxy connections. However, if a 3DES encryption algorithm and
2k key length are used (which are becoming more common), the throughput may be halved.
Decision: Pre-Authentication Policy
An optional pre-authentication policy may be applied to user groups with NetScaler Gateway as their authentication point (this design decision is not applicable for non-NetScaler Gateway authentication
points). Pre-authentication policies limit access to the environment based on whether the endpoint meets certain criteria through
Endpoint Analysis (EPA) Scans.
Pre-authentication access policies can be configured to test antivirus, firewall, operating system, or even registry settings. These policies are used by XenDesktop to control features such as clipboard mapping, printer mapping and even the availability of specific applications and desktops. For example, if a user device does not have antivirus installed, a filter can be set to hide sensitive
applications.