Overview

A redundant Ethernet interface (reth) is a pseudointerface that includes at minimum one physical interface from each node of the cluster, it is pretty similar to aggregated ethernet interfaces that we use on routers.
A redundant Ethernet interface inherits its failover properties from the redundancy group x that it belongs to. A redundant Ethernet interface remains active as long as its primary child interface is available or active. For example, if reth0 is associated with redundancy group 1 and redundancy group 1 is active on node 0, then reth0 is up as long as the node 0 child of reth0 is up.

Useful commands

#> show chassis cluster interfaces
Control link status: Up

Control interfaces:
   Index    Interface    Monitored-Status    Internal-SA    Security
   0        em0          Up                  Disabled       Disabled

Fabric link status: Up

Fabric interfaces:
   Name    Child-interface    Status                  Security
                              (Physical/Monitored)
   fab0    xe-0/0/17          Up / Up                 Disabled
   fab0
   fab1    xe-7/0/17          Up / Up                 Disabled
   fab1

Redundant-ethernet Information:
   Name    Status    Redundancy-group
   reth0   Up        1
   reth1   Down      Not configured

Redundant-pseudo-interface Information:
   Name    Status    Redundancy-group
   lo0     Up        0

Interface Monitoring:
   Interface    Weight    Status                 Redundancy-group
                          (Physical/Monitored)
   xe-7/0/19    255       Up / Up                1
   xe-0/0/19    255       Up / Up                1

Configuration example

#> show configuration chassis
cluster {
   reth-count 2;
   redundancy-group 0 {
      node 0 priority 100;
      node 1 priority 1;
   }
   redundancy-group 1 {
      node 0 priority 100;
      node 1 priority 1;
      preempt;
      interface-monitor {
         xe-0/0/19 weight 255;
         xe-7/0/19 weight 255;
      }
   }
}

#> show configuration interfaces reth0
   description "To dist-L3";
   flexible-vlan-tagging;
   mtu 9192;
   gratuitous-arp-reply;
   redundant-ether-options {
      redundancy-group 1;
      minimum-links 1;
   }
unit 1 {
   description "description";
   vlan-id 1;
   family inet {
      mtu 1600;
      address 10.20.50.6/29;
   }
}

#> show configuration interfaces xe-0/0/19
   description "reth0 1/2";
   gigether-options {
      redundant-parent reth0;
   }

#> show configuration interfaces xe-7/0/19
   description "reth0 2/2";
   gigether-options {
      redundant-parent reth0;
   }