Concordia University/CSE Concordia University/CSE This document proposes some additions to the specification of the Protocol Independent Multicast - Sparse Mode (PIM-SM) Protocol regarding security issues of its link-local messages. Although the new specifications for IPsec architecture (RFC 4301) and Authorization Header (RFC 4302) permit the use of anti-replay, they counsel against its use for multi-sender, multicast Security Associations. This makes PIM-SM vulnerable to Denial of Service (DoS) attack. In this document, a new proposal is presented to protect PIM link-local messages while activating the anti-replay mechanism as well. This proposal builds on the new Security Association lookup method that has been specified in RFC 4301 and RFC 4302.