stickydr

Syntax

Hierarchy Level

Description

The stickydr feature protects against traffic loss as can happen when the designated router (DR) changes once a new router joins the LAN and/or following an interface down event, or device upgrade. Set stickydr on all the last hop devices in the LAN, and it will assign one DR special priority (that is, 0xfffffffe, the second highest priority) irrespective of existing DR election logic (DM priority and IP address of PIM neighbors). The sticky DR priority remains with the device until it is explicitly transferred to another eligible device on the LAN.

This feature is especially useful for countering DR elections cases wherein a new interface on the LAN appears, immediately wins the DR election, and even before it has received an IGMP join from host, starts pulling traffic from the upstream router.

Consider the example of a new device with higher DM priority and/or IP address that joins the LAN. Instead of immediately ceding DR status to the new interface, an existing device with a lower IP address and/or lower priority can remain the DR and receive IGMP joins and send PIM joins upstream. When the new device (with higher priority or IP address) appears, it detects the sticky DR and joins as a non-DR. No traffic is lost because of a DR transition.

Another example is when a DR interface goes down. If the devices in the LAN were configured for stickydr, a new DR election amongst the remaining PIM routers will take place as usual, and as per the RFC, but the election winner will inherit the “sticky” property of the down DR when wins. The sticky status will persist even if another device with higher priority joins the LAN. Later, when the previous DR comes back up, it’s DR status is not resumed.

Required Privilege Level

routing—To view this statement in the configuration.

routing-control—To add this statement to the configuration.

Release Information

Statement introduced in Junos OS Release 18.3R1.