# Unexpected Suspension of Subscriber Login and Logouts During Unified ISSU

All new subscriber logins are ignored during the upgrade phase. New subscriber logouts are cached and processed after the unified ISSU operation is completed.

## Subscriber Statistics Accumulation or Deletion

All subscriber statistics present in the line modules are cleared when the line module forwarding planes are upgraded. For this reason, the router has to read the statistics from the forwarding plane before it is upgraded.

However, forwarding through the line modules continues after that point, until the line module forwarding plane is upgraded. Some statistics can therefore accumulate in the forwarding plane in the interval between these two events. These statistics are not preserved across the upgrade.

Statistics for subscribers that log out during the forwarding plane upgrade are collected and reported before the forwarding plane is reloaded. Statistics are not collected for any subscribers who are connected before you issue the issu start command but who log out before the forwarding plane upgrade is completed.

The following subscriber statistics are preserved across the upgrade:

- All policy statistics
- Accounting statistics reported by IP: in bytes, out bytes, in packets, out packets
- Accounting statistics reported by L2TP: in octets, out octets, in packets, out packets
- Accounting statistics reported by PPP: in octets, out octets, in packets, out packets

All other statistics are set to zero, including all statistics belonging to the SNMP generic interface MIB for every interface layer.

#### Related Documentation

- Application Support for Unified ISSU