# Unexpected Ethernet Behavior During Unified ISSU

The following aspects of Ethernet behavior during a unified in-service software upgrade are different than during normal router operations.

## ARP Packets Briefly Not Sent or Received

There is a brief period at the end of the upgrade phase when ARP packets are not sent or received. This event can affect ARP entries on attached devices that were in the process of being aged out.

## Link Aggregation Interruption

During the unified in-service software upgrade, LACP PDUs are not generated or received for about 15 seconds on Ethernet ports configured with LACP.

This interruption has no effect on the local side of the link because JunosE Software generates LAC PDU packets every 30 seconds. The link is not declared down unless packets are missed three times. LACP packet generation continues when the unified ISSU operation is completed.

If a device on the other end of the link is configured with the short timeout, then the device is likely to declare the link to be down and remove the link from the LAG bundle.

## Port Data Rate Monitoring Halted

The monitoring of Ethernet port data rate is halted during a unified in-service software upgrade. Monitoring resumes immediately after the unified ISSU operation is completed. The data rates reported by the show interface command are inaccurate for the period of one configured load interval after unified ISSU is completed.

## VLAN Statistics Monitoring Halts Unified ISSU Progress

A unified in-service software upgrade cannot proceed if VLAN statistics monitoring is in progress.

#### Related Documentation

- Application Support for Unified ISSU