The trace query must be sent to the multicast router that is the last hop on the path from the source to the receiver. If the receiver is on the local subnet (as determined by the subnet mask), then the default method is to send the trace query to all-routers.mcast.net (224.0.0.2) with a TTL of 1. Otherwise, the trace query is sent to the group address since the last-hop router will be a member of that group if the receiver is. Therefore, it is necessary to specify a group that the intended receiver has joined. This multicast query is sent with a default TTL of 64, which may not be sufficient for all cases.
When tracing from a multihomed host or router, the default receiver address may not be the required interface for the path from the source. In that case, the required interface should be specified explicitly as the receiver.