code: func (p *peer) AsyncSendNewBlock(block *types.Block, td *big.Int) {
  	select {
  	case p.queuedProps <- &propEvent{block: block, td: td}:
  		p.knownBlocks.Add(block.Hash())
  	default:
  		p.Log().Debug("Dropping block propagation", "number", block.NumberU64(), "hash", block.Hash())
  	}
  }
docs: // AsyncSendNewBlock queues an entire block for propagation to a remote peer. If
  // the peer's broadcast queue is full, the event is silently dropped.