If a switch is in slave mode, it exchanges ESRP packets with other switches on that same VLAN.
When a switch is in slave mode, it does not perform Layer 3 routing or Layer 2 switching services for the VLAN. From a Layer 3 routing protocol perspective (for example, RIP or OSPF), when in slave mode for the VLAN, the switch marks the router interface associated with that VLAN as down. From a Layer 2 switching perspective, no forwarding occurs between the member ports of the VLAN; this prevents loops and maintains redundancy.
If you configure the switch to use the optional ESRP Host Attach configuration, the switch continues Layer 2 forwarding to the master. For more information, see ESRP Host Attach.