The BGP routes used in the MVPN procedures have a Subsequent Address Family Identifier (SAFI) value of 5, or MCAST-VPN. The Network Layer Reachability Information (NLRI) format for MCAST-VPN routes consists of a Route Type (RT) field and depending on the RT, a Route Distinguisher (RD) Extended Community (EC) field.
To distinguish MCAST-VPN routes originated for VPNs from MCAST-VPN routes in support of GTM, the RD field, if defined within that route’s NLRI, must be set to zero (that is, 64 bits of zero). An RD of all zeros associates that route with GTM, as no VRF can have an RD of zero.
MVPN procedures use two types of RTs, one of which is carried only in the routes of C-multicast shared tree joins, C-multicast source tree joins, and leaf auto-discovery routes (A-D routes). This RT type identifies the PE router that has been selected by the route’s originator as the Upstream PE or as the Upstream Multicast Hop (UMH) for a particular multicast flow or set of multicast flows. This RT must be an IPv4- or IPv6-address-specific EC, where the Global Administrator field identifies the Upstream PE or the UMH. If the Global Administrator field identifies the Upstream PE, the Local Administrator field identifies a particular VRF in that PE.
To support GTM, this type of RT is used in the same situations as in the MVPN specifications, with the modification that the Local Administrator field of this RT type must always be set to zero. This implicitly identifies the global table instead of identifying a VRF. This type of RT is referred to as an upstream-node-identifying RT.