Techniques are described for grouping related flows using a flow attribute value indicated by a modified protocol independent multicast (PIM) join request. According to techniques of this disclosure, a network device is configured to receive, from a downstream network device, two or more first PIM join requests indicating two or more multicast groups. In response to determining that each first PIM join request of the two or more first PIM join requests indicates a common first flow attribute value, the network device is configured to select a common path. The network device is further configured to send two or more second PIM join requests indicating the two or more multicast groups to an upstream network device along the selected common path and toward the source. Each second PIM join request of the two or more second PIM join requests includes a common second flow attribute value.