Akamai Technologies This document updates RFC 7450 (AMT) by extending the relay discovery process to use a new DNS resource record for source-specific AMT relay discovery when joining source-specific multicast channels. A multicast sender configures a reverse IP DNS zone with the new AMTRELAY RR (defined in this document) to advertise a set of relays that can receive and forward multicast traffic from that sender inside a unicast AMT tunnel, in order to transit non-multicast- capable network segments.