Traffic Load Balancer

Transparent Mode Layer 2 Direct Server Return

When you use transparent mode Layer 2 direct server return (DSR):

• The PFE processes data.

• Load balancing works by changing the Layer 2 MAC of packets.

• An MS-MPC performs the network-monitoring probes.

• Real servers must be directly (Layer 2) reachable from the MX Series router.

• TLB installs a route and all the traffic over that route is load-balanced.

• TLB never modifies Layer 3 and higher level headers.

Figure 1 shows the TLB topology for transparent mode Layer 2 DSR.

Figure 1: TLB Topology for Transparent Mode

Translated Mode

Translated mode provides greater flexibility than transparent mode Layer 2 DSR. When you choose translated mode:

• An MS-MPC performs the network-monitoring probes.

• The PFE performs stateless load balancing:

  • Data traffic directed to a virtual IP address undergoes translation of the virtual IP address to a real server IP address and translates the virtual port to a server listening port. Return traffic undergoes the reverse translation.

  • Client to virtual IP traffic is translated; the traffic is routed to reach its destination.

  • Server-to-client traffic is captured using implicit filters and directed to an appropriate load-balancing next hop for reverse processing. After translation, traffic is routed back to the client.

  • Two load balancing methods are available: random and hash. The random method is only for UDP traffic and provides quavms-random distribution. While not literally random, this mode provides fair distribution of traffic to an available set of servers. The hash method provides a hash key based on any combination of the source IP address, destination IP address, and protocol.

    Note:

    Translated mode processing is only available for IPv4-to-IPv4 and IPv6-to-IPv6 traffic.

Figure 2 shows the TLB topology for translated mode.

Figure 2: TLB Topology for Translated Mode

Transparent Mode Layer 3 Direct Server Return

Transparent mode Layer 3 DSR load balancing distributes sessions to servers that can be a Layer 3 hop away. Traffic is returned directly to the client from the real-server.

Servers and Server Groups

TLB enables configuration of groups of up to 255 servers (referred to in configuration statements as real services) for use as alternate destinations for stateless session distribution. All servers used in server groups must be individually configured before assignment to groups. Load balancing uses hashing or randomization for session distribution. Users can add and delete servers to and from the TLB server distribution table and can also change the administrative status of a server.

Server Health Monitoring — Single Health Check and Dual Health Check

TLB supports TCP, HTTP, SSL Hello, TLS Hello, and custom health check probes to monitor the health of servers in a group. You can use a single probe type for a server group, or a dual health check configuration that includes two probe types. The configurable health monitoring function resides on either an MX-SPC3 or an MS-MPC. By default, probe requests are sent every 5 seconds. Also by default, a real server is declared down only after five consecutive probe failures and declared up only after five consecutive probe successes.

Use a custom health check probe to specify the following:

• Expected string in the probe response

• String that is sent with the probe

• Server status to assign when the probe times out (up or down)

• Server status to assign when the expected response to the probe is received (up or down)

• Protocol — UDP or TCP

TLB provides application stickiness, meaning that server failures or changes do not affect traffic flows to other active servers. Changing a server’s administrative state from up to down does not impact any active flows to remaining servers in the server distribution table. Adding a server or deleting a server from a group has some traffic impact for a length of time that depends on your configuration of the interval and retry parameters in the monitoring profile.

TLB provides two levels of server health monitoring:

• Single Health Check—One probe type is attached to a server group by means of the network-monitoring-profile configuration statement.

• TLB Dual Health Check (TLB-DHC)—Two probe types are associated with a server group by means of the network-monitoring-profile configuration statement. A server’s status is declared based on the result of two health check probes. Users can configure up to two health check profiles per server group. If a server group is configured for dual health check, a real-service is declared to be UP only when both health-check probes are simultaneously UP; otherwise, a real-service is declared to be DOWN.

Routing Engine-Based Health Check for Traffic Load Balancer

Traffic Load Balancer (TLB) for next generation MX routers is capable of running the health check process on the Routing Engine (RE) too. This feature is applicable for both MSP and USF.

To enable the health-check process (net-monitord) on RE, you can use the new command, set services traffic-load-balance routing-engine-mode. This configuration and the TLB change ensure that the process responsible for managing and orchestrating traffic distribution and redirection connects to the local instance of the network monitoring process instead of the remote instance running on the service-PIC.

The health-check probe types that are supported on the RE-based health-checks are ICMP, TCP, UDP, HTTP, and SSL probes.

The new feature requires modification to the TLB configuration. Loopback interface is used instead of the service interface.

Virtual Services

The virtual service provides a virtual IP address (VIP) that is associated with the group of servers to which traffic is directed as determined by hash-based or random session distribution and server health monitoring. In the case of L2 DSR and L3 DSR, the special address 0.0.0.0 causes all traffic flowing to the forwarding instance to be load balanced.

The virtual service configuration includes:

• Mode—indicating how traffic is handled (translated or transparent).

• The group of servers to which sessions are distributed.

• The load balancing method.

• Routing instance and route metric.