Zevachim 119 - The Resting Place and the Inheritance
Moses said that there will be periods when private altars will be permitted, " for you have not yet come to the resting place or to the inheritance ." The "resting place" refers to Shiloh, and "the inheritance" refers to Jerusalem. When the Tabernacle stood either in Shiloh or Jerusalem, private altars were forbidden. However, before that, at Gilgal, and between these time period, when it stood in Nov and Giveon, private altars were permitted.
According to Rabbi Yishmael, both "resting place" and "inheritance" refer to Shiloh, and no verse is needed to teach that private altars were permitted in between, because we find many righteous individual using them. According to Rabbi Shimon, both refer to Jerusalem, and private altars were always permitted before then.
Private altar does not require leaning on the sacrifice, or the northern side of the altar, or application of blood all around the altar, or waving the offering, or bringing the flour offering to the southern corner of the altar. Rabbi Yehudah says that there are no flour offerings on a private altar.
Art: John William Waterhouse - A Roman Offering