A monitoring platform can report very high OutUtilization values for an IRB logical interface when it uses the IRB's reported bandwidth as the interface speed.

In the reviewed case, the IRB reported 1 Gbps while the VLAN was carried through a 40 Gbps physical interface. The 1 Gbps value on the IRB was informational and did not represent a physical forwarding limit.

Important: The IRB bandwidth value can be used by monitoring systems for utilization calculations, even though the IRB is a logical interface.

• Monitoring alerts show IRB output utilization above 100%, sometimes several hundred percent.
• The monitoring platform detects the IRB speed as 1000 Mbps.
• The IRB is associated with a VLAN carried by a higher-speed physical interface.
• The physical interface can show no input/output errors or drops, with no evidence of physical link congestion.

Critical - Interface irb.<unit> OutUtilization is 691.8285% (>= 300)

Interface Speed: 1000 Mbps

> show interfaces irb.<unit> extensive

Logical interface irb.<unit>

  Bandwidth: 1Gbps

> show interfaces et-<fpc>/<pic>/<port> extensive

Physical interface: et-<fpc>/<pic>/<port>, Enabled, Physical link is Up

  Speed: 40Gbps

  Input errors: Errors: 0, Drops: 0

  Output errors: Errors: 0, Drops: 0

1-- Confirm the bandwidth reported by the IRB and compare it with the physical interface carrying the VLAN.

show interfaces irb.<unit> extensive

show vlans <vlan-name>

show interfaces et-<fpc>/<pic>/<port> extensive

2-- If the monitoring platform is using the IRB's 1 Gbps value and the intended reference bandwidth is 40 Gbps, update the IRB informational bandwidth.

set interfaces irb unit <unit> bandwidth 40g

This change is informational only. It does not increase, reduce, shape, or limit the actual forwarding capacity of the IRB.

3-- If the IRB participates in OSPF, verify the current OSPF behavior before and after the change.

show configuration protocols ospf | display set | match "reference-bandwidth|irb.<unit>"

show ospf interface irb.<unit> detail

OSPF note: In the reviewed case there was no explicit OSPF metric or custom reference bandwidth. With default OSPF values, the metric was expected to remain 1 when changing the IRB bandwidth from 1 Gbps to 40 Gbps.

4-- After the change, verify the IRB reports the intended bandwidth and confirm the monitoring platform updates the interface speed.

show interfaces irb.<unit> extensive

  Bandwidth: 40Gbps

show ospf interface irb.<unit> detail

If the monitoring platform continues to show 1000 Mbps after the Junos change, refresh or rediscover the interface from the monitoring side.

https://www.juniper.net/documentation/us/en/software/junos/cli-reference/topics/ref/statement/bandwidth-edit-interfaces.html