Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?


Overview of Uplink Failure Detection on a Junos Fusion

The uplink failure detection feature on a Junos Fusion enables satellite devices to detect link failures on the uplink interfaces used to connect to aggregation devices. When uplink failure detection detects uplink failure on a satellite device, all of the device’s extended ports (which connect to host devices) are shut down. Shutting down the extended ports allows downstream host devices to more quickly identify and adapt to the outage. For example, when a host device is connected to two satellite devices, and uplink failure detection shuts down the extended ports on one satellite device, the host device can more quickly recognize the uplink failure and redirect traffic through the other, active satellite device.

You can configure uplink failure detection globally, for all satellite devices of a Junos Fusion, and for individual satellite devices. Uplink failure detection configuration at the satellite device level overrides the global uplink failure detection configuration.

Uplink failure detection configuration allows you to configure these options:

  • The minimum number of active uplink ports a satellite device must have to remain active. The default is one active uplink port. You can use this option to specify more minimum active ports.

  • The amount of time uplink failure detection waits to try to re-enable disabled extended ports. This wait time is called a hold-down period. It is intended to avoid port flapping on the extended ports when uplink port connectivity is unstable. The default hold-down period is six seconds.

Uplink failure detection must know which ports on a satellite device can be used as uplink ports. These are called candidate uplink ports. Table 1 shows the default set of candidate uplink ports that uplink failure detection selects for failure detection. If you choose not to use the default uplink ports for your satellite devices, you need to specify which uplink ports you want to use for uplink failure detection by creating a candidate uplink port profile and applying it to the satellite device’s uplink failure detection configuration.


The physically connected uplink ports on a satellite device must be defined as candidate uplink ports in the Junos Fusion configuration. If the uplink ports on a satellite device are not configured as candidate uplink ports, uplink failure detection cannot be enabled on the device, and a system log message is generated.

Table 1: UFD Default Uplink Interfaces for Satellite Devices

Device Type

Default Uplink Interfaces

EX4300-24T (4 ports each on PIC1 and PIC2)

1/0 through 1/3 and 2/0 through 2/3

EX4300-32F (4 ports on PIC 0, 2 ports on PIC 1 and 8 ports on PIC 2)

0/32 through 0/35

1/0 through 1/1

2/0 through 2/7

EX4300-48T (4 ports each on PIC1 and PIC2)

1/0 through 1/3 and 2/0 through 2/3

EX4300-48T-BF (4 ports each on PIC1 and PIC2)

1/0 through 1/3 and 2/0 through 2/3

QFX5100-24Q-2P (4 ports on PIC 0)

0/20 through 0/23

QFX5100-48S-6Q (6 QSFP+ ports)

0/48 through 0/53

QFX5100-48T-6Q (6 QSFP+ ports)

0/48 through 0/53

QFX5100-96S-8Q (8 QSFP+ ports)

0/96 through 0/103