diff --git a/p2p/async-buffer/src/lib.rs b/p2p/async-buffer/src/lib.rs
index ded8c6a9..0e2ced24 100644
--- a/p2p/async-buffer/src/lib.rs
+++ b/p2p/async-buffer/src/lib.rs
@@ -48,7 +48,7 @@ pub fn new_buffer<T>(max_item_weight: usize) -> (BufferAppender<T>, BufferStream
             queue: tx,
             sink_waker: sink_waker.clone(),
             capacity: capacity_atomic.clone(),
-            max_item_weight: capacity,
+            max_item_weight,
         },
         BufferStream {
             queue: rx,
diff --git a/p2p/cuprate-p2p/src/block_downloader.rs b/p2p/cuprate-p2p/src/block_downloader.rs
index 0cae8a74..49618434 100644
--- a/p2p/cuprate-p2p/src/block_downloader.rs
+++ b/p2p/cuprate-p2p/src/block_downloader.rs
@@ -1,29 +1,38 @@
 //! # Block Downloader
 //!
 
-use std::collections::VecDeque;
+mod chain_tracker;
+
+use std::collections::{BTreeMap, BinaryHeap, VecDeque};
 use std::sync::Arc;
+use std::time::Duration;
 
 use monero_serai::{block::Block, transaction::Transaction};
 use rand::prelude::*;
 use tokio::task::JoinSet;
+use tokio::time::{interval, MissedTickBehavior};
 use tower::{Service, ServiceExt};
 
+use crate::block_downloader::chain_tracker::{ChainEntry, ChainTracker};
 use async_buffer::{BufferAppender, BufferStream};
+use fixed_bytes::ByteArrayVec;
+use monero_p2p::client::InternalPeerID;
 use monero_p2p::{
     handles::ConnectionHandle,
     services::{PeerSyncRequest, PeerSyncResponse},
     NetworkZone, PeerRequest, PeerResponse, PeerSyncSvc,
 };
-use monero_wire::protocol::ChainRequest;
+use monero_wire::protocol::{ChainRequest, ChainResponse};
 
-use crate::client_pool::ClientPool;
-use crate::constants::INITIAL_CHAIN_REQUESTS_TO_SEND;
+use crate::client_pool::{ClientPool, ClientPoolDropGuard};
+use crate::constants::{INITIAL_CHAIN_REQUESTS_TO_SEND, MEDIUM_BAN};
 
 /// A downloaded batch of blocks.
 pub struct BlockBatch {
     /// The blocks.
-    blocks: (Block, Vec<Transaction>),
+    blocks: Vec<(Block, Vec<Transaction>)>,
+    /// The size of this batch in bytes.
+    size: usize,
     /// The peer that gave us this block.
     peer_handle: ConnectionHandle,
 }
@@ -36,12 +45,20 @@ pub struct BlockDownloaderConfig {
     buffer_size: usize,
     /// The size of the in progress queue at which we stop requesting more blocks.
     in_progress_queue_size: usize,
+    /// The [`Duration`] between checking the client pool for free peers.
+    check_client_pool_interval: Duration,
+    /// The target size of a single batch of blocks (in bytes).
+    target_batch_size: usize,
+    /// The initial amount of blocks to request (in number of blocks)
+    initial_batch_size: usize,
 }
 
-#[derive(Debug, Copy, Clone, PartialOrd, PartialEq, Ord, Eq, thiserror::Error)]
+#[derive(Debug, thiserror::Error)]
 pub enum BlockDownloadError {
     #[error("Failed to find a more advanced chain to follow")]
     FailedToFindAChainToFollow,
+    #[error("The peer did not send any overlapping blocks, unknown start height.")]
+    PeerSentNoOverlappingBlocks,
     #[error("Service error: {0}")]
     ServiceError(#[from] tower::BoxError),
 }
@@ -52,6 +69,8 @@ pub enum ChainSvcRequest {
     CompactHistory,
     /// A request to find the first unknown
     FindFirstUnknown(Vec<[u8; 32]>),
+
+    CumulativeDifficulty,
 }
 
 /// The response type for the chain service.
@@ -64,6 +83,8 @@ pub enum ChainSvcResponse {
     /// The response for [`ChainSvcRequest::FindFirstUnknown`], contains the index of the first unknown
     /// block.
     FindFirstUnknown(usize),
+
+    CumulativeDifficulty(u128),
 }
 
 /// # Block Downloader
@@ -83,6 +104,7 @@ pub fn download_blocks<N: NetworkZone, S>(
 ) -> BufferStream<BlockBatch> {
     let (buffer_appender, buffer_stream) = async_buffer::new_buffer(config.buffer_size);
 
+    /*
     tokio::spawn(block_downloader(
         client_pool,
         peer_sync_svc,
@@ -90,33 +112,89 @@ pub fn download_blocks<N: NetworkZone, S>(
         buffer_appender,
     ));
 
+     */
+
     buffer_stream
 }
 
-async fn block_downloader<N: NetworkZone, S>(
+struct BlockDownloader<N: NetworkZone, S, C> {
     client_pool: Arc<ClientPool<N>>,
+
     peer_sync_svc: S,
-    config: BlockDownloaderConfig,
+    our_chain_svc: C,
+
+    block_download_tasks: JoinSet<()>,
+    chain_entry_task: JoinSet<()>,
+
     buffer_appender: BufferAppender<BlockBatch>,
-) -> Result<(), tower::BoxError> {
-    todo!()
+
+    config: BlockDownloaderConfig,
 }
 
-struct BestChainFound {
-    common_ancestor: [u8; 32],
-    next_hashes: VecDeque<[u8; 32]>,
-    from_peer: ConnectionHandle,
+async fn block_downloader<N: NetworkZone, S, C>(
+    client_pool: Arc<ClientPool<N>>,
+    mut peer_sync_svc: S,
+    mut our_chain_svc: C,
+    config: BlockDownloaderConfig,
+    buffer_appender: BufferAppender<BlockBatch>,
+) -> Result<(), BlockDownloadError>
+where
+    S: PeerSyncSvc<N> + Clone,
+    C: Service<ChainSvcRequest, Response = ChainSvcResponse, Error = tower::BoxError>
+        + Send
+        + 'static,
+    C::Future: Send + 'static,
+{
+    let mut best_chain_found =
+        initial_chain_search(&client_pool, peer_sync_svc.clone(), &mut our_chain_svc).await?;
+
+    let tasks = JoinSet::new();
+
+    let mut ready_queue = BinaryHeap::new();
+    let mut inflight_queue = BTreeMap::new();
+
+    let mut next_request_id = 0;
+
+    // The request ID for which we updated `amount_of_blocks_to_request`
+    // `amount_of_blocks_to_request` will update for every new batch of blocks that come in.
+    let mut amount_of_blocks_to_request_updated_at = next_request_id;
+
+    // The amount of blocks to request in 1 batch, will dynamically update based on block size.
+    let mut amount_of_blocks_to_request = config.initial_batch_size;
+
+    let mut check_client_pool_interval = interval(config.check_client_pool_interval);
+    check_client_pool_interval.set_missed_tick_behavior(MissedTickBehavior::Delay);
+
+    loop {
+        tokio::select! {
+            _ = check_client_pool_interval.tick() => {
+                todo!()
+            }
+
+
+
+        }
+    }
+}
+
+async fn handle_free_peer<N: NetworkZone>(
+    peer: ClientPoolDropGuard<N>,
+    chain_tracker: &mut ChainTracker<N>,
+    next_batch_size: usize,
+) {
+    if chain_tracker.block_requests_queued(next_batch_size) < 15
+        && chain_tracker.should_ask_for_next_chain_entry(&peer.info.pruning_seed)
+    {}
 }
 
 async fn initial_chain_search<N: NetworkZone, S, C>(
-    client_pool: &ClientPool<N>,
+    client_pool: &Arc<ClientPool<N>>,
     mut peer_sync_svc: S,
     mut our_chain_svc: C,
-) -> Result<BestChainFound, BlockDownloadError>
+) -> Result<ChainTracker<N>, BlockDownloadError>
 where
     S: PeerSyncSvc<N>,
-    C: Service<ChainSvcRequest, Response = ChainSvcResponse> + Send + 'static,
-    C::Future: Send + 'static,
+    C: Service<ChainSvcRequest, Response = ChainSvcResponse, Error = tower::BoxError>,
 {
     let ChainSvcResponse::CompactHistory {
         block_ids,
@@ -130,6 +208,8 @@ where
         panic!("chain service sent wrong response.");
     };
 
+    let our_genesis = *block_ids.last().expect("Blockchain had no genesis block.");
+
     let PeerSyncResponse::PeersToSyncFrom(mut peers) = peer_sync_svc
         .ready()
         .await?
@@ -165,14 +245,17 @@ where
                 panic!("connection task returned wrong response!");
             };
 
-            Ok((chain_res, next_peer.info.handle.clone()))
+            Ok((chain_res, next_peer.info.id, next_peer.info.handle.clone()))
         });
     }
 
-    let mut res = None;
+    let mut res: Option<(ChainResponse, InternalPeerID<_>, ConnectionHandle)> = None;
 
     while let Some(task_res) = futs.join_next().await {
-        let Ok(task_res) = task_res.unwrap() else {
+        let Ok(task_res): Result<
+            (ChainResponse, InternalPeerID<_>, ConnectionHandle),
+            tower::BoxError,
+        > = task_res.unwrap() else {
             continue;
         };
 
@@ -188,11 +271,14 @@ where
         }
     }
 
-    let Some((chain_res, peer_handle)) = res else {
+    let Some((chain_res, peer_id, peer_handle)) = res else {
         return Err(BlockDownloadError::FailedToFindAChainToFollow);
     };
 
-    let hashes: Vec<[u8; 32]> = chain_res.m_block_ids.into();
+    let hashes: Vec<[u8; 32]> = (&chain_res.m_block_ids).into();
+    let start_height = chain_res.start_height;
+    // drop this to deallocate the [`Bytes`].
+    drop(chain_res);
 
     let ChainSvcResponse::FindFirstUnknown(first_unknown) = our_chain_svc
         .ready()
@@ -202,7 +288,19 @@ where
     else {
         panic!("chain service sent wrong response.");
     };
-    
-    todo!()
-    
+
+    if first_unknown == 0 {
+        peer_handle.ban_peer(MEDIUM_BAN);
+        return Err(BlockDownloadError::PeerSentNoOverlappingBlocks);
+    }
+
+    let first_entry = ChainEntry {
+        ids: hashes[first_unknown..].to_vec(),
+        peer: peer_id,
+        handle: peer_handle,
+    };
+
+    let tracker = ChainTracker::new(first_entry, start_height, our_genesis);
+
+    Ok(tracker)
 }
diff --git a/p2p/cuprate-p2p/src/block_downloader/chain_tracker.rs b/p2p/cuprate-p2p/src/block_downloader/chain_tracker.rs
new file mode 100644
index 00000000..a325905e
--- /dev/null
+++ b/p2p/cuprate-p2p/src/block_downloader/chain_tracker.rs
@@ -0,0 +1,182 @@
+use fixed_bytes::ByteArrayVec;
+use std::{cmp::min, collections::VecDeque};
+
+use monero_p2p::{client::InternalPeerID, handles::ConnectionHandle, NetworkZone};
+use monero_pruning::{PruningSeed, CRYPTONOTE_MAX_BLOCK_HEIGHT};
+use monero_wire::protocol::ChainResponse;
+
+use crate::constants::MEDIUM_BAN;
+
+/// A new chain entry to add to our chain tracker.
+#[derive(Debug)]
+pub(crate) struct ChainEntry<N: NetworkZone> {
+    /// A list of block IDs.
+    pub ids: Vec<[u8; 32]>,
+    /// The peer who told us about this chain entry.
+    pub peer: InternalPeerID<N::Addr>,
+    /// The peer who told us about this chain entry's handle
+    pub handle: ConnectionHandle,
+}
+
+/// A batch of blocks to retrieve.
+pub struct BlocksToRetrieve<N: NetworkZone> {
+    /// The block IDs to get.
+    pub ids: ByteArrayVec<32>,
+    /// The expected height of the first block in `ids`.
+    pub start_height: u64,
+    /// The peer who told us about this batch.
+    pub peer_who_told_us: InternalPeerID<N::Addr>,
+    /// The peer who told us about this batch's handle.
+    pub peer_who_told_us_handle: ConnectionHandle,
+}
+
+pub enum ChainTrackerError {
+    NewEntryIsInvalid,
+    NewEntryDoesNotFollowChain,
+}
+
+/// # Chain Tracker
+///
+/// This struct allows following a single chain. It takes in [`ChainEntry`]s and
+/// allows getting [`BlocksToRetrieve`].
+pub struct ChainTracker<N: NetworkZone> {
+    /// A list of [`ChainEntry`]s, in order.
+    entries: VecDeque<ChainEntry<N>>,
+    /// The height of the first block, in the first entry in entries.
+    first_height: u64,
+    /// The hash of the last block in the last entry.
+    top_seen_hash: [u8; 32],
+    /// The hash of the genesis block.
+    our_genesis: [u8; 32],
+}
+
+impl<N: NetworkZone> ChainTracker<N> {
+    pub fn new(new_entry: ChainEntry<N>, first_height: u64, our_genesis: [u8; 32]) -> Self {
+        let top_seen_hash = *new_entry.ids.last().unwrap();
+        let mut entries = VecDeque::with_capacity(1);
+        entries.push_back(new_entry);
+
+        Self {
+            top_seen_hash,
+            entries,
+            first_height,
+            our_genesis,
+        }
+    }
+
+    /// Returns `true` if the peer is expected to have the next block after our highest seen block
+    /// according to their pruning seed.
+    pub fn should_ask_for_next_chain_entry(&self, seed: &PruningSeed) -> bool {
+        let top_block_idx = self
+            .entries
+            .iter()
+            .map(|entry| entry.ids.len())
+            .sum::<usize>();
+
+        seed.has_full_block(
+            self.first_height + u64::try_from(top_block_idx).unwrap(),
+            CRYPTONOTE_MAX_BLOCK_HEIGHT,
+        )
+    }
+
+    /// Returns the simple history, the highest seen block and the genesis block.
+    pub fn get_simple_history(&self) -> [[u8; 32]; 2] {
+        [self.top_seen_hash, self.our_genesis]
+    }
+
+    /// Returns the total number of queued batches for a certain `batch_size`.
+    pub fn block_requests_queued(&self, batch_size: usize) -> usize {
+        self.entries
+            .iter()
+            .map(|entry| entry.ids.len().div_ceil(batch_size))
+            .sum()
+    }
+
+    pub fn add_entry(
+        &mut self,
+        mut chain_entry: ChainResponse,
+        peer: InternalPeerID<N::Addr>,
+        handle: ConnectionHandle,
+    ) -> Result<(), ChainTrackerError> {
+        // TODO: check chain entries length.
+        if chain_entry.m_block_ids.is_empty() {
+            // The peer must send at lest one overlapping block.
+            handle.ban_peer(MEDIUM_BAN);
+            return Err(ChainTrackerError::NewEntryIsInvalid);
+        }
+
+        if self
+            .entries
+            .back()
+            .is_some_and(|last_entry| last_entry.ids.last().unwrap() != &chain_entry.m_block_ids[0])
+        {
+            return Err(ChainTrackerError::NewEntryDoesNotFollowChain);
+        }
+
+        tracing::warn!("len: {}", chain_entry.m_block_ids.len());
+
+        let new_entry = ChainEntry {
+            // ignore the first block - we already know it.
+            ids: (&chain_entry.m_block_ids.split_off(1)).into(),
+            peer,
+            handle,
+        };
+
+        self.top_seen_hash = *new_entry.ids.last().unwrap();
+
+        self.entries.push_back(new_entry);
+
+        Ok(())
+    }
+
+    pub fn blocks_to_get(
+        &mut self,
+        pruning_seed: &PruningSeed,
+        max_blocks: usize,
+    ) -> Option<BlocksToRetrieve<N>> {
+        if !pruning_seed.has_full_block(self.first_height, CRYPTONOTE_MAX_BLOCK_HEIGHT) {
+            return None;
+        }
+
+        // TODO: make sure max block height is enforced.
+
+        let entry = self.entries.front_mut()?;
+
+        // Calculate the ending index for us to get in this batch, will be the smallest out of `max_blocks`, the length of the batch or
+        // the index of the next pruned block for this seed.
+        let end_idx = min(
+            min(entry.ids.len(), max_blocks),
+            usize::try_from(
+                pruning_seed
+                    .get_next_pruned_block(self.first_height, CRYPTONOTE_MAX_BLOCK_HEIGHT)
+                    // We check the first height is less than CRYPTONOTE_MAX_BLOCK_HEIGHT in response task.
+                    .unwrap()
+                    // Use a big value as a fallback if the seed does no pruning.
+                    .unwrap_or(CRYPTONOTE_MAX_BLOCK_HEIGHT)
+                    - self.first_height,
+            )
+            .unwrap(),
+        );
+
+        if end_idx == 0 {
+            return None;
+        }
+
+        let ids_to_get = entry.ids.drain(0..end_idx).collect::<Vec<_>>();
+
+        let blocks = BlocksToRetrieve {
+            ids: ids_to_get.into(),
+            start_height: self.first_height,
+            peer_who_told_us: entry.peer,
+            peer_who_told_us_handle: entry.handle.clone(),
+        };
+
+        self.first_height += u64::try_from(end_idx).unwrap();
+
+        if entry.ids.is_empty() {
+            self.entries.pop_front();
+        }
+
+        Some(blocks)
+    }
+}
diff --git a/p2p/cuprate-p2p/src/client_pool.rs b/p2p/cuprate-p2p/src/client_pool.rs
index ed547dde..49ba768e 100644
--- a/p2p/cuprate-p2p/src/client_pool.rs
+++ b/p2p/cuprate-p2p/src/client_pool.rs
@@ -138,13 +138,16 @@ impl<N: NetworkZone> ClientPool<N> {
     pub fn borrow_clients<'a, 'b>(
         self: &'a Arc<Self>,
         peers: &'b [InternalPeerID<N::Addr>],
-    ) -> impl Iterator<Item = ClientPoolDropGuard<N>> + Captures<(&'a (), &'b ())> {
+    ) -> impl Iterator<Item = ClientPoolDropGuard<N>> + sealed::Captures<(&'a (), &'b ())> {
         peers.iter().filter_map(|peer| self.borrow_client(peer))
     }
 }
 
-/// TODO: Remove me when 2024 Rust
-///
-/// https://rust-lang.github.io/rfcs/3498-lifetime-capture-rules-2024.html#the-captures-trick
-trait Captures<U> {}
-impl<T: ?Sized, U> Captures<U> for T {}
+mod sealed {
+    /// TODO: Remove me when 2024 Rust
+    ///
+    /// https://rust-lang.github.io/rfcs/3498-lifetime-capture-rules-2024.html#the-captures-trick
+    pub trait Captures<U> {}
+
+    impl<T: ?Sized, U> Captures<U> for T {}
+}
diff --git a/p2p/cuprate-p2p/src/constants.rs b/p2p/cuprate-p2p/src/constants.rs
index 9bf9abc9..df6f5ee7 100644
--- a/p2p/cuprate-p2p/src/constants.rs
+++ b/p2p/cuprate-p2p/src/constants.rs
@@ -12,6 +12,9 @@ pub(crate) const OUTBOUND_CONNECTION_ATTEMPT_TIMEOUT: Duration = Duration::from_
 /// The durations of a short ban.
 pub(crate) const SHORT_BAN: Duration = Duration::from_secs(60 * 10);
 
+/// The durations of a medium ban.
+pub(crate) const MEDIUM_BAN: Duration = Duration::from_secs(60 * 10 * 24);
+
 /// The default amount of time between inbound diffusion flushes.
 pub(crate) const DIFFUSION_FLUSH_AVERAGE_SECONDS_INBOUND: Duration = Duration::from_secs(5);