Propagation is not validation. A Full Node independently checks consensus rules before accepting a block into its active chain; fast announcement or delivery does not prove validity.
A miner announces a new block to connected peers. The method depends on negotiated protocol and relay mode, not one mandatory network route. [Bitcoin Developer Guide — P2P Network] [BIP 152 — Compact Block Relay]
A receiver can request a full block or reconstruct it from compact relay. The result must contain the same complete block data needed for validation. [Bitcoin Developer Guide — P2P Network] [BIP 152 — Compact Block Relay]
A header shows the previous-block link and allows checking Proof of Work. It does not by itself prove all transaction validity or UTXO state. [Bitcoin Developer Guide — P2P Network] [Satoshi Nakamoto — Bitcoin whitepaper]
BIP 152 uses transactions the receiver already knows, for example from its mempool. Short identifiers reduce repeated transmission of whole transactions without changing the consensus block's contents. [BIP 152 — Compact Block Relay]
Missing transactions are requested through additional messages. Savings depend on local data availability; reconstruction can require another round trip or a full-block fallback. [BIP 152 — Compact Block Relay] [Bitcoin Core v29.0 — net processing]
BIP 152 high-bandwidth mode allows forwarding after specified preliminary checks before full validation. A Full Node must still fully validate the block before accepting it into the active chain. [BIP 152 — Compact Block Relay] [Bitcoin Core v29.0 — net processing]
During propagation, other miners can find a competing block at the same height. Subsequent work chooses among valid branches; faster relay narrows this window but does not eliminate it. [Bitcoin Developer Guide — P2P Network] [Satoshi Nakamoto — Bitcoin whitepaper]
Poor connectivity can increase the risk of a miner's block remaining outside the accepted chain. Fast-relay advantages can encourage concentration, but are not themselves a measurement of centralization. [Bitcoin FIBRE] [Satoshi Nakamoto — Bitcoin whitepaper]
FIBRE exemplifies specialized low-latency relay. A different delivery path does not give its operator authority to decide block validity for a Full Node. [Bitcoin FIBRE] [Bitcoin Core v29.0 — net processing]
Operation balances speed, data volume, privacy and path resilience. BIP 330 concerns transaction-set reconciliation in transaction relay; it does not replace BIP 152 compact block relay. [BIP 152 — Compact Block Relay] [BIP 330 — Erlay]
For the clearest picture, read this entry together with Compact block relay, Selfish mining, Eclipse attack, Initial block download. The reverse links also lead from Stale block, Selfish mining, Compact block relay, Orphan Block.