EPL and EPLAN are the two most common configurations for the EFGS. They process some protocol packets (such as STP packets) in different ways. Improper processing may lead to protocol packet loop, which in turn causes network storm.
1. STP packets usually do not carry a VLAN tag. If tag aware is configured on the port, STP packets are dropped in the case of the EPL configuration or transparently transmitted in the case of the EPLAN configuration. This means that the EPL configuration processes STP packets and common packets in the same way (check the VLAN tag). For the EVPLAN services, if the STP is enabled, the packets are processed. If the STP is disabled, the STP multicasts the protocol packets regarless of VLAN tags.
2. The EPL service performs point-to-point forwarding of STP packets according to the configuration, which means the EPLs are isolated. The EPLAN service broadcasts STP packets to all the ports in the VB despite of the VLAN ID.
3. The EPL service does not process the source MAC address of STP packets, but the EPLAN service replaces the source MAC address of STP packets with the MAC address of the board.