Supported Platforms
Understanding Aggregated Multiservices Interfaces
This topic contains the following sections:
Aggregated Multiservices Interface
In Junos OS, you can combine multiple services interfaces to create a bundle of interfaces that can function as a single interface. Such a bundle of interfaces is known as an aggregated multiservices interface (AMS), and is denoted as amsN in the configuration, where N is a unique number that identifies an AMS interface (for example, ams0).
AMS configuration provides higher scalability, improved performance, and better failover and load-balancing options.
The current service set configuration model in Junos OS supports only one service PIC per service set. All services provisioned using a service set must be handled by the only one service PIC associated with that service set. AMS configuration enables you to address this limitation by associating an AMS bundle with a service set. An AMS bundle can have up to eight services PICs as member interfaces and can distribute services among the member interfaces. This allows you to have multiple service interfaces to handle services configured in one service set.
 | Note: Member interfaces are identified as mams in the configuration. The chassisd process in routers that support AMS configuration creates a mams entry each for every multiservices interface on the router. |
Traffic distribution in an AMS bundle is achieved by means of user-configurable hash keys. You can configure the following hash key values: source-ip, destination-ip, iif (incoming interface), oif (outgoing interface), and protocol. For services that require traffic symmetry, you must configure symmetrical hashing. Symmetrical hashing configuration ensures that both forward and reverse traffic are routed through the same member interface.
| Note: Junos OS AMS configuration supports only IPv4 traffic. |
Member Failure Options and High Availability Settings
Because multiple service interfaces are configured as part of an AMS bundle, AMS configuration also provides for failover and high availability support. You can either configure one of the member interfaces as a backup interface that becomes active when any one of the other member interfaces goes down, or configure the AMS in such a way that when one of the member interfaces goes down, the traffic assigned to that interface is shared across the active interfaces.
The member-failure-options configuration statement enables you to configure how to handle traffic when a member interface fails. One option is to redistribute the traffic immediately among the other member interfaces. However, redistribution of traffic involves recalculating the hash tags, and might cause some disruption in traffic on all the member interfaces.
The other option is to configure the AMS to drop all traffic that is assigned to the failed member interface. With this you can optionally configure an interval, rejoin-timeout, for the AMS to wait for the failed interface to come back online after which the AMS can redistribute the traffic among other member interfaces. If the failed member interface comes back online before the configured wait time, traffic continues unaffected on all member interfaces, including the interface that has come back online and resumed the operations.
You can also control the rejoining of the failed interface when it comes back online. If you do not include the enable-rejoin statement in the member-failure-options configuration, the failed interface is not allowed to rejoin the AMS when it comes back online. In such cases, you can manually rejoin that to the AMS by executing the request interfaces revert interface-name operational mode command.
The rejoin-timeout and enable-rejoin statements enable you to minimize traffic disruptions when member interfaces flap.
| Note: When member-failure-options are not configured, the default behavior is to redistribute the traffic among the available interfaces. |
The high-availability-options configuration enables you to designate one of the member interfaces as a backup interface. The backup interface does not participate in routing operations as long as it remains a backup interface. When a member interface fails, the backup interface handles the traffic assigned to the failed interface. When the failed interface comes back online, it becomes the new backup interface.
When both member-failure-options and high-availability-options are configured for an AMS, the high-availability-options configuration takes precedence over the member-failure-options configuration. If a second failure occurs before the failed interface comes back online to be the new backup, the member-failure-options configuration comes into effect.
