diff --git a/core/src/NetServer.cpp b/core/src/NetServer.cpp
new file mode 100644
index 0000000..cb9d8b3
--- /dev/null
+++ b/core/src/NetServer.cpp
@@ -0,0 +1,185 @@
+#include "vf/NetServer.h"
+
+#include <cmath>
+
+namespace vf {
+
+namespace {
+
+Vec3i chunkOfPosition(const Vec3& position) {
+    int gx = static_cast<int>(std::floor(position.x));
+    int gy = static_cast<int>(std::floor(position.y));
+    int gz = static_cast<int>(std::floor(position.z));
+    return Vec3i{floorDiv(gx, chunkSize), floorDiv(gy, chunkSize), floorDiv(gz, chunkSize)};
+}
+
+}  // namespace
+
+NetServer::NetServer(World& world, ServerConfig config) : worldRef(&world), config(config) {
+    if (this->config.maxClients == 0) this->config.maxClients = 1;
+    slots.resize(this->config.maxClients);
+}
+
+uint32_t NetServer::activeClients() const {
+    uint32_t count = 0;
+    for (const ClientSlot& slot : slots)
+        if (slot.active) ++count;
+    return count;
+}
+
+bool NetServer::isActive(int slot) const {
+    if (slot < 0 || static_cast<std::size_t>(slot) >= slots.size()) return false;
+    return slots[static_cast<std::size_t>(slot)].active;
+}
+
+int NetServer::acceptClient() {
+    for (std::size_t i = 0; i < slots.size(); ++i) {
+        ClientSlot& slot = slots[i];
+        if (slot.active) continue;
+
+        SessionConfig sessionConfig;
+        sessionConfig.protocolVersion = config.protocolVersion;
+        sessionConfig.viewRadius = config.viewRadius;
+        sessionConfig.chunksPerTick = config.chunksPerClientPerTick;
+        sessionConfig.keepAliveIntervalTicks = config.keepAliveIntervalTicks;
+        sessionConfig.keepAliveTimeoutTicks = config.keepAliveTimeoutTicks;
+        sessionConfig.multiBlockThreshold = config.multiBlockThreshold;
+        sessionConfig.bandwidthBytesPerTick = config.bytesPerClientPerTick;
+        sessionConfig.maxPlayers = static_cast<uint8_t>(config.maxClients);
+        sessionConfig.seedHash = config.seedHash;
+        sessionConfig.levelType = config.levelType;
+
+        slot.active = true;
+        slot.entityId = static_cast<int32_t>(i) + 1;
+        slot.lastBytesFlushed = 0;
+        slot.lastChunksSent = 0;
+        slot.lastBlockUpdates = 0;
+        slot.link.reset(new LoopbackLink(config.link));
+        slot.transport.reset(new Transport(*slot.link, 0, config.transport));
+        slot.session.reset(new NetSession(*slot.transport, NetSession::Role::Server, sessionConfig));
+        slot.session->attachWorld(*worldRef);
+        slot.session->attachChunkSync(sync);
+        slot.session->setEntityId(slot.entityId);
+
+        ++statistics.acceptedConnections;
+        return static_cast<int>(i);
+    }
+    ++statistics.rejectedConnections;
+    return -1;
+}
+
+void NetServer::dropClient(int slot) {
+    if (!isActive(slot)) return;
+    ClientSlot& entry = slots[static_cast<std::size_t>(slot)];
+    entry.active = false;
+    entry.session.reset();
+    entry.transport.reset();
+    entry.link.reset();
+}
+
+LoopbackLink* NetServer::linkFor(int slot) {
+    if (!isActive(slot)) return nullptr;
+    return slots[static_cast<std::size_t>(slot)].link.get();
+}
+
+NetSession* NetServer::sessionFor(int slot) {
+    if (!isActive(slot)) return nullptr;
+    return slots[static_cast<std::size_t>(slot)].session.get();
+}
+
+void NetServer::applyEdit(const BlockChange& change) {
+    worldRef->setBlock(change.x, change.y, change.z, change.block);
+    Vec3i coord{floorDiv(change.x, chunkSize), floorDiv(change.y, chunkSize),
+                floorDiv(change.z, chunkSize)};
+    sync.markDirty(coord, floorMod(change.x, chunkSize), floorMod(change.y, chunkSize),
+                   floorMod(change.z, chunkSize));
+    for (ClientSlot& slot : slots)
+        if (slot.active) slot.session->markChunkDirty(coord);
+    ++statistics.editsApplied;
+}
+
+void NetServer::setBlock(int gx, int gy, int gz, Block block) {
+    BlockChange change;
+    change.x = gx;
+    change.y = gy;
+    change.z = gz;
+    change.block = block;
+    applyEdit(change);
+}
+
+void NetServer::moveEntity(int32_t entityId, const Vec3& position, float yaw, float pitch,
+                           bool onGround) {
+    Vec3i coord = chunkOfPosition(position);
+    for (ClientSlot& slot : slots) {
+        if (!slot.active) continue;
+        if (slot.session->phase() != SessionPhase::Play) continue;
+        // An entity outside the client's view costs nothing to skip and cannot
+        // be drawn there anyway.
+        if (!slot.session->view().tracker.contains(coord)) continue;
+        slot.session->sendEntityMove(entityId, position, yaw, pitch, onGround);
+    }
+}
+
+void NetServer::collectStats() {
+    statistics.bytesSentThisTick = 0;
+    statistics.queuedPackets = 0;
+    statistics.queuedBytes = 0;
+    for (ClientSlot& slot : slots) {
+        if (!slot.active) continue;
+        const SessionStats& sessionStats = slot.session->stats();
+
+        uint64_t bytes = sessionStats.bytesFlushed - slot.lastBytesFlushed;
+        slot.lastBytesFlushed = sessionStats.bytesFlushed;
+        statistics.bytesSentThisTick += bytes;
+        statistics.totalBytesSent += bytes;
+
+        uint64_t chunks = sessionStats.chunksSent - slot.lastChunksSent;
+        slot.lastChunksSent = sessionStats.chunksSent;
+        statistics.chunksSent += chunks;
+
+        uint64_t updates = sessionStats.blockChangesSent + sessionStats.multiBlockChangesSent;
+        statistics.blockUpdatesSent += updates - slot.lastBlockUpdates;
+        slot.lastBlockUpdates = updates;
+
+        statistics.queuedPackets += slot.session->queuedPacketCount();
+        statistics.queuedBytes += slot.session->queuedByteCount();
+    }
+}
+
+void NetServer::reap() {
+    for (std::size_t i = 0; i < slots.size(); ++i) {
+        ClientSlot& slot = slots[i];
+        if (!slot.active) continue;
+        if (slot.session->phase() != SessionPhase::Disconnected) continue;
+        if (slot.session->timedOut()) ++statistics.timeouts;
+        dropClient(static_cast<int>(i));
+    }
+}
+
+void NetServer::update(uint64_t tick) {
+    for (ClientSlot& slot : slots) {
+        if (!slot.active) continue;
+        slot.session->receive(tick);
+        slot.lastServicedTick = tick;
+    }
+
+    // Upstream edits land in the world before any session builds its outgoing
+    // packets, so every client sees the same authoritative state this tick.
+    for (ClientSlot& slot : slots) {
+        if (!slot.active) continue;
+        for (const BlockChange& change : slot.session->requestedEdits()) applyEdit(change);
+        slot.session->clearRequestedEdits();
+    }
+
+    for (ClientSlot& slot : slots) {
+        if (!slot.active) continue;
+        slot.session->send(tick);
+    }
+
+    sync.clearAll();
+    collectStats();
+    reap();
+    statistics.connectedClients = activeClients();
+}
+
+} // namespace vf