JUNOS Enterprise Switching

Redundant Trunk Groups

Another feature that can help in loops is a feature called Redundant Trunk Groups (RTGs). Essentially, RTGs provide a fast and simplified Layer 2 failover mechanism, without introducing the complexity of running STP. RTG allows for one physical (or LAG) interface to back up another in case of a failure.

Note

In the Cisco world, RTG is often referred to as FlexLink.

One of the most common situations in which to use RTG is when an access layer switch is dual-homed to the aggregation or distribution switch (Figure 6-36). In this scenario, configuration is needed only on the local Switch C, as Switch A and Switch B do not need to know that RTG is enabled. However, if a link is enabled for RTG, it cannot participate in STP nor does it need to, as you manually solved the issue that STP was trying to solve. If STP was allowed on interfaces running RTG, confusion could occur if the active link suddenly became blocked due to an STP calculation. JUNOS software will display a commit error if STP and RTG are attempted at the same time:

[edit ethernet-switching-options]
lab@Brandy# commit
error: XSTP : msti 0 STP and RTG cannot be enabled on the same interface ge-0/0/1.0
error: configuration check-out failed

Figure 6-36. Common deployment scenario for RTG

RTG Configuration

RTG is configured under [edit ethernet-switching-options] and defines two interfaces under a group: a primary ...