# IPv6 Behavior During Unified ISSU

Unified ISSU supports IPv6 instances. You can perform ISSU on E Series routers without disconnecting IPv6 subscriber connections. IPv6 traffic forwarding through the chassis experiences minimal disruption. IPv6 configuration is retained after the upgrade and all IPv6 and dual-stack subscriber sessions established prior to performing ISSU remain established.

IPv6 applications can send and receive control plane traffic during the unified ISSU operation except during SRP module upgrade and forwarding controller upgrade phases. IPv6 data plane traffic forwarding will continue after the unified ISSU operation with minimal traffic forwarding outages during ISSU. Since dynamically learned neighbor entries are not mirrored during ISSU, they have to be relearned after ISSU. This causes longer traffic forwarding outages for IPv6 applications when compared to IPv4 applications.

#### Related Documentation

- Application Support for Unified ISSU
- Interruption in Traffic Forwarding for Layer 3 Routing Protocols During Unified ISSU
- Unified ISSU Overview