Network Load Balancing
Encyclopedia
Network load balancing is the ability to balance traffic across two WAN
links without using complex routing protocols like BGP
.
This capability balances network sessions like Web, email, etc. over multiple connections in order to spread out the amount of bandwidth used by each LAN
user, thus increasing the total amount of bandwidth available. For example, a user has a single WAN connection to the Internet
operating at 1.5Mbit/s. They wish to add a second broadband (cable, DSL, wireless, etc.) connection operating at 2.5Mbit/s. This would provide them with a total of 4Mbit/s of bandwidth when balancing sessions.
Session balancing does just that, it balances sessions across each WAN link. When Web browsers connect to the Internet, they commonly open multiple sessions, one for the text, another for an image, another for some other image, etc. Each of these sessions can be balanced across the available connections. An FTP
application only uses a single session so it is not balanced; however if a secondary FTP connection is made, then it may be balanced so that on the whole, traffic is evenly distributed across the various connections and thus provides an overall increase in throughput.
Additionally, network load balancing is commonly used to provide network redundancy so that in the event of a WAN link outage, access to network resources is still available via the secondary link(s). Redundancy is a key requirement for business continuity
plans and generally used in conjunction with critical applications like VPNs and VoIP.
Finally, most network load balancing systems also incorporate the ability to balance both outbound and inbound traffic. Inbound load balancing is generally performed via dynamic DNS which can either be built into the system, or provided by an external service or system. Having the dynamic DNS service within the system is generally thought to be better from a cost savings and overall control point of view.
. Clusters can use network load balancing whereby simultaneous cluster request are distributed between cluster servers.
Round robin DNS records is one form of cluster load balancing. It works by creating multiple host records (usually A and/or AAAA) for one machine. As clients make requests, DNS rotates through its list of records.
In addition to the before mentioned, to configure a terminal server cluster, one needs a load-balancing technology such as Network Load Balancing (NLB) or DNS round robin. A load balancing solution will distribute client connections to each of the terminal servers.
Terminal Server Session Directory is a feature that allows users to easily and automatically reconnect to a disconnected session in a load balanced Terminal Server farm. The session directory keeps a list of sessions indexed by username and server name. This enables a user, after disconnecting a session, to reconnect to the correct Terminal Server where the disconnected session resides in order to resume working in that session.
This reconnection will work even if the user connects from a different client computer.
Wide area network
A wide area network is a telecommunication network that covers a broad area . Business and government entities utilize WANs to relay data among employees, clients, buyers, and suppliers from various geographical locations...
links without using complex routing protocols like BGP
Border Gateway Protocol
The Border Gateway Protocol is the protocol backing the core routing decisions on the Internet. It maintains a table of IP networks or 'prefixes' which designate network reachability among autonomous systems . It is described as a path vector protocol...
.
This capability balances network sessions like Web, email, etc. over multiple connections in order to spread out the amount of bandwidth used by each LAN
Local area network
A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...
user, thus increasing the total amount of bandwidth available. For example, a user has a single WAN connection to the Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
operating at 1.5Mbit/s. They wish to add a second broadband (cable, DSL, wireless, etc.) connection operating at 2.5Mbit/s. This would provide them with a total of 4Mbit/s of bandwidth when balancing sessions.
Session balancing does just that, it balances sessions across each WAN link. When Web browsers connect to the Internet, they commonly open multiple sessions, one for the text, another for an image, another for some other image, etc. Each of these sessions can be balanced across the available connections. An FTP
File Transfer Protocol
File Transfer Protocol is a standard network protocol used to transfer files from one host to another host over a TCP-based network, such as the Internet. FTP is built on a client-server architecture and utilizes separate control and data connections between the client and server...
application only uses a single session so it is not balanced; however if a secondary FTP connection is made, then it may be balanced so that on the whole, traffic is evenly distributed across the various connections and thus provides an overall increase in throughput.
Additionally, network load balancing is commonly used to provide network redundancy so that in the event of a WAN link outage, access to network resources is still available via the secondary link(s). Redundancy is a key requirement for business continuity
Business continuity
Business continuity is the activity performed by an organization to ensure that critical business functions will be available to customers, suppliers, regulators, and other entities that must have access to those functions. These activities include many daily chores such as project management,...
plans and generally used in conjunction with critical applications like VPNs and VoIP.
Finally, most network load balancing systems also incorporate the ability to balance both outbound and inbound traffic. Inbound load balancing is generally performed via dynamic DNS which can either be built into the system, or provided by an external service or system. Having the dynamic DNS service within the system is generally thought to be better from a cost savings and overall control point of view.
Microsoft NLB
Microsoft has also developed a technology called Network Load Balancing (NLB) that allows for efficient utilization of multiple network cards.Server load balancing
When multiple servers are joined to create a clusterCluster (computing)
A computer cluster is a group of linked computers, working together closely thus in many respects forming a single computer. The components of a cluster are commonly, but not always, connected to each other through fast local area networks...
. Clusters can use network load balancing whereby simultaneous cluster request are distributed between cluster servers.
Round robin DNS records is one form of cluster load balancing. It works by creating multiple host records (usually A and/or AAAA) for one machine. As clients make requests, DNS rotates through its list of records.
In addition to the before mentioned, to configure a terminal server cluster, one needs a load-balancing technology such as Network Load Balancing (NLB) or DNS round robin. A load balancing solution will distribute client connections to each of the terminal servers.
Terminal Server Session Directory is a feature that allows users to easily and automatically reconnect to a disconnected session in a load balanced Terminal Server farm. The session directory keeps a list of sessions indexed by username and server name. This enables a user, after disconnecting a session, to reconnect to the correct Terminal Server where the disconnected session resides in order to resume working in that session.
This reconnection will work even if the user connects from a different client computer.