Simple Loop Prevention Protocol (SLPP) in computer networking is a Data Link Layer protocol developed by Nortel (previously acquired by Avaya, now a part of by Extreme Networks) to protect against Layer 2 network loops. SLPP uses a small hello packet to detect network loops. The SLPP protocol checks packets from the originating switch and the peer switch in a SMLT configuration. Sending hello packets on a per VLAN basis allows SLPP to detect VLAN based network loops for un-tagged as well as tagged IEEE 802.1Q VLAN link configurations. If a loop is detected, the associated port is shut down.