We study the performance of reliable and unreliable all-node broadcast over ad-hoc networks that use contention-based channel access. To obtain analytical results while preserving hidden-terminal and node clustering characteristics of ah-hoc networks, we introduce a novel differential-equation fluid model for information flow through a network of cluster trees, where a spanning tree joins groups of fully connected nodes. Through numerical analysis and simulations in GloMoSim, we show throughput, goodput, and loss rates for reliable and unreliable networks. For reliable broadcast, we also find NAK rates, NAK loss rates, and retransmission rates. We show that using end-to-end sequence numbers, which are common in reliable multicast, for NAK generation in ad-hoc networks creates substantial unnecessary traffic.