Network load balancing
Network load balancing (also known as dual WAN routing) is the ability to balance traffic over two WAN links without using complex routing protocols such as BGP .
This ability balances out sessions such as web, email, etc. over multiple connections to expand the bandwidth used by each WAN user and thus increase the total available bandwidth. For example, a user has a single WAN connection to the Internet with a bandwidth of 1.5Mbit / s. He wants to add a second broadband (cable, DSL, WLan etc.) connection with 2.5Mbit / s. This would result in a total bandwidth of 4Mbit / s if the sessions are balanced.
Balancing sessions means balancing the sessions across every WAN link. When web browsers connect to the Internet, they usually open several sessions: one for text, one for an image, one for another image, etc. Each of these sessions can be balanced using the existing connections. An FTP application only uses a single session and is therefore unbalanced; however, if another FTP connection is established, it can be balanced in such a way that data traffic is generally evenly distributed over different connections, thus increasing the overall throughput.
Network load balancing is also widely used to provide redundancy so that even if one WAN link fails, the connection to resources on the network will still be available through other connection (s). Redundancy is an essential prerequisite for business continuity plans and is generally used in conjunction with critical applications such as VPNs or VoIP .
Most network load balancing systems also include the ability to balance both inbound and outbound traffic. Incoming load distribution is usually carried out using DDNS or made available by an external system or service. Having a DDNS service within a system is generally perceived as better from the standpoint of cost / benefit and general control.
Microsoft NLB
Microsoft has also bought a technology that it has renamed Network Load Balancing (NLB), which enables multiple network cards to be used efficiently. MS NLB can be configured in both unicast and multicast mode, whereby IGMP snooping can be activated in multicast mode .
MS NLB was introduced in Windows NT server to distribute data traffic over multiple hosts without the need for a hardware-based load balancer, e.g. For example, when hosting a busy web server application where a single host could not handle all traffic. And in newer applications it is used in Windows Cluster for Hyper-V or Microsoft SQL Server .
Unicast mode
In unicast mode, NLB changes the station's MAC address (depending on the primary IP address of the NLB cluster) to a virtual MAC address and all network cards in the NLB cluster use this one MAC address. This structure will cause any incoming data traffic for the cluster to flood all ports of the switch as unknown unicast frames, even ports connected to the hosts that do not belong to the cluster. In order to keep the flooding as low as possible, a separate VLAN would have to be used for the cluster.
Multicast mode
Another possibility is to operate NLB in multicast mode. The cluster's unicast IPv4 address is associated with the multicast Mac address. The hosts of the cluster will not send any data to the switch with this MAC and IPv4 address, so you would have to create a static ARP entry in the router (layer 3). Not all manufacturers allow ARP entries to be created where a unicast IP address and a multicast MAC address are used. Cisco has published examples of how to set up MS NLB on Catalyst switches with Cisco IOS , and these examples can be used with switches from many other manufacturers. As with NLB in unicast mode, the following applies: Incoming data traffic to the cluster is flooded to all ports in the switch / VLAN and not all manufacturers support this structure. In order to minimize the flood of data, IGMP is now supported by MS NLB, which should lead to the switches learning which ports actually use a multicast address, but this does not always lead to the desired result. For example, the Dell PowerConnect Multi-Layer Switches do not officially support MS NLB Multicast. It works, but results in high CPU usage - which affects (other) traffic in the switch and other switches can have other restrictions, such as the switch that the NLB network cards are connected to cannot be the same switch that Handles IP routing.
Server load balancing
Several servers are connected to form a cluster. Clusters can use network load balancing, with simultaneous cluster requests being distributed between the clusters. DNS load balancing is a form of cluster load balancing. It works by creating multiple host entries (usually A and / or AAAA) for a machine. When clients make queries, DNS rotates through its list of entries. In addition to the above, to configure a terminal server cluster, someone needs a load balancing technology like network load balancing (NLB) or load balancing via DNS. Such a solution will distribute the client connections to all terminal servers. Terminal Server Session Directory is a function that allows users in a terminal server farm with load balancing to easily and automatically connect to a previously interrupted session. The session directory keeps a list of sessions, indexed with user name and server name. This authorizes the user to reconnect to the terminal server where the interrupted session is located in order to resume the interrupted work. This reconnection works even if the user is connecting from another computer.
See also
Individual evidence
- ↑ Microsoft purchases clustering company. Retrieved May 16, 2017 .
- ↑ TechNet Network Load Balancing (overview). Retrieved May 16, 2017 .
- ↑ VMWare knowledge base: MS NLB in unicast and multicast mode. Retrieved May 16, 2017 .
- ↑ Cisco: Catalyst configuration examples. Retrieved May 16, 2017 .
- ↑ Microsoft Support knowledge base: KB283028: IGMP Snooping support on NLB. Retrieved May 16, 2017 .
- ↑ Dell Tech Communities: Trying to limit switch flooding from a Microsoft Windows Network Load Balacing (NLB). (No longer available online.) Archived from the original on October 5, 2013 ; accessed on May 16, 2017 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
