diff --git a/src/yggdrasil/config/config.go b/src/yggdrasil/config/config.go
index 5a081b6..ef5f7c2 100644
--- a/src/yggdrasil/config/config.go
+++ b/src/yggdrasil/config/config.go
@@ -16,6 +16,7 @@ type NodeConfig struct {
 	IfName                      string              `comment:"Local network interface name for TUN/TAP adapter, or \"auto\" to select\nan interface automatically, or \"none\" to run without TUN/TAP."`
 	IfTAPMode                   bool                `comment:"Set local network interface to TAP mode rather than TUN mode if\nsupported by your platform - option will be ignored if not."`
 	IfMTU                       int                 `comment:"Maximux Transmission Unit (MTU) size for your local TUN/TAP interface.\nDefault is the largest supported size for your platform. The lowest\npossible value is 1280."`
+	SessionFirewall             SessionFirewall     `comment:"The session firewall controls who can send/receive network traffic\nto/from. This is useful if you want to protect this node without\nresorting to using a real firewall. This does not affect traffic\nbeing routed via this node to somewhere else."`
 	//Net                         NetConfig `comment:"Extended options for connecting to peers over other networks."`
 }
 
@@ -24,3 +25,11 @@ type NetConfig struct {
 	Tor TorConfig `comment:"Experimental options for configuring peerings over Tor."`
 	I2P I2PConfig `comment:"Experimental options for configuring peerings over I2P."`
 }
+
+type SessionFirewall struct {
+	Enable                        bool     `comment:"Enable or disable the session firewall. If disabled, network traffic\nfrom any node will be allowed. If enabled, the below rules apply."`
+	AllowFromDirect               bool     `comment:"Allow network traffic from directly connected peers."`
+	AllowFromRemote               bool     `comment:"Allow network traffic from remote nodes on the network that you are\nnot directly peered with."`
+	WhitelistEncryptionPublicKeys []string `comment:"List of public keys from which network traffic is always accepted,\nregardless of AllowFromDirect or AllowFromRemote."`
+	BlacklistEncryptionPublicKeys []string `comment:"List of public keys from which network traffic is always rejected,\nregardless of the whitelist, AllowFromDirect or AllowFromRemote."`
+}
diff --git a/src/yggdrasil/core.go b/src/yggdrasil/core.go
index 224bad9..64dff63 100644
--- a/src/yggdrasil/core.go
+++ b/src/yggdrasil/core.go
@@ -107,6 +107,11 @@ func (c *Core) Start(nc *config.NodeConfig, log *log.Logger) error {
 		return err
 	}
 
+	c.sessions.setSessionFirewallState(nc.SessionFirewall.Enable)
+	c.sessions.setSessionFirewallDefaults(nc.SessionFirewall.AllowFromDirect, nc.SessionFirewall.AllowFromRemote)
+	c.sessions.setSessionFirewallWhitelist(nc.SessionFirewall.WhitelistEncryptionPublicKeys)
+	c.sessions.setSessionFirewallBlacklist(nc.SessionFirewall.BlacklistEncryptionPublicKeys)
+
 	if err := c.router.start(); err != nil {
 		c.log.Println("Failed to start router")
 		return err
diff --git a/src/yggdrasil/peer.go b/src/yggdrasil/peer.go
index f0dd3d0..35a73cd 100644
--- a/src/yggdrasil/peer.go
+++ b/src/yggdrasil/peer.go
@@ -17,7 +17,7 @@ import (
 type peers struct {
 	core                        *Core
 	mutex                       sync.Mutex   // Synchronize writes to atomic
-	ports                       atomic.Value //map[Port]*peer, use CoW semantics
+	ports                       atomic.Value //map[switchPort]*peer, use CoW semantics
 	authMutex                   sync.RWMutex
 	allowedEncryptionPublicKeys map[boxPubKey]struct{}
 }
diff --git a/src/yggdrasil/session.go b/src/yggdrasil/session.go
index 7a33226..3ed118b 100644
--- a/src/yggdrasil/session.go
+++ b/src/yggdrasil/session.go
@@ -6,6 +6,7 @@ package yggdrasil
 
 import (
 	"bytes"
+	"encoding/hex"
 	"time"
 )
 
@@ -107,6 +108,12 @@ type sessions struct {
 	byTheirPerm  map[boxPubKey]*handle
 	addrToPerm   map[address]*boxPubKey
 	subnetToPerm map[subnet]*boxPubKey
+	// Options from the session firewall
+	sessionFirewallEnabled      bool
+	sessionFirewallAllowsDirect bool
+	sessionFirewallAllowsRemote bool
+	sessionFirewallWhitelist    []string
+	sessionFirewallBlacklist    []string
 }
 
 // Initializes the session struct.
@@ -121,6 +128,77 @@ func (ss *sessions) init(core *Core) {
 	ss.lastCleanup = time.Now()
 }
 
+// Enable or disable the session firewall
+func (ss *sessions) setSessionFirewallState(enabled bool) {
+	ss.sessionFirewallEnabled = enabled
+}
+
+// Set the session firewall defaults (first parameter is whether to allow
+// sessions from direct peers, second is whether to allow from remote nodes).
+func (ss *sessions) setSessionFirewallDefaults(allowsDirect bool, allowsRemote bool) {
+	ss.sessionFirewallAllowsDirect = allowsDirect
+	ss.sessionFirewallAllowsRemote = allowsRemote
+}
+
+// Set the session firewall whitelist - nodes always allowed to open sessions.
+func (ss *sessions) setSessionFirewallWhitelist(whitelist []string) {
+	ss.sessionFirewallWhitelist = whitelist
+}
+
+// Set the session firewall blacklist - nodes never allowed to open sessions.
+func (ss *sessions) setSessionFirewallBlacklist(blacklist []string) {
+	ss.sessionFirewallBlacklist = blacklist
+}
+
+// Determines whether the session with a given publickey is allowed based on
+// session firewall rules.
+func (ss *sessions) isSessionAllowed(pubkey *boxPubKey) bool {
+	// Allow by default if the session firewall is disabled
+	if !ss.sessionFirewallEnabled {
+		return true
+	}
+	// Prepare for checking whitelist/blacklist
+	var box boxPubKey
+	// Reject blacklisted nodes
+	for _, b := range ss.sessionFirewallBlacklist {
+		key, err := hex.DecodeString(b)
+		if err == nil {
+			copy(box[:boxPubKeyLen], key)
+			if box == *pubkey {
+				return false
+			}
+		}
+	}
+	// Allow whitelisted nodes
+	for _, b := range ss.sessionFirewallWhitelist {
+		key, err := hex.DecodeString(b)
+		if err == nil {
+			copy(box[:boxPubKeyLen], key)
+			if box == *pubkey {
+				return true
+			}
+		}
+	}
+	// Look and see if the pubkey is that of a direct peer
+	var isDirectPeer bool
+	for _, peer := range ss.core.peers.ports.Load().(map[switchPort]*peer) {
+		if peer.box == *pubkey {
+			isDirectPeer = true
+			break
+		}
+	}
+	// Allow direct peers if appropriate
+	if ss.sessionFirewallAllowsDirect && isDirectPeer {
+		return true
+	}
+	// Allow remote nodes if appropriate
+	if ss.sessionFirewallAllowsRemote && !isDirectPeer {
+		return true
+	}
+	// Finally, default-deny if not matching any of the above rules
+	return false
+}
+
 // Gets the session corresponding to a given handle.
 func (ss *sessions) getSessionForHandle(handle *handle) (*sessionInfo, bool) {
 	sinfo, isIn := ss.sinfos[*handle]
@@ -311,6 +389,12 @@ func (ss *sessions) sendPingPong(sinfo *sessionInfo, isPong bool) {
 func (ss *sessions) handlePing(ping *sessionPing) {
 	// Get the corresponding session (or create a new session)
 	sinfo, isIn := ss.getByTheirPerm(&ping.SendPermPub)
+	// Check the session firewall
+	if ss.sessionFirewallEnabled {
+		if !ss.isSessionAllowed(&ping.SendPermPub) {
+			return
+		}
+	}
 	if !isIn || sinfo.timedout() {
 		if isIn {
 			sinfo.close()
diff --git a/src/yggdrasil/tcp.go b/src/yggdrasil/tcp.go
index 1942acd..0bc5802 100644
--- a/src/yggdrasil/tcp.go
+++ b/src/yggdrasil/tcp.go
@@ -164,7 +164,7 @@ func (iface *tcpInterface) call(saddr string, socksaddr *string, sintf string) {
 				if err != nil {
 					return
 				} else {
-					if ief.Flags & net.FlagUp == 0 {
+					if ief.Flags&net.FlagUp == 0 {
 						return
 					}
 					addrs, err := ief.Addrs()
diff --git a/yggdrasil.go b/yggdrasil.go
index 7102824..447bb3e 100644
--- a/yggdrasil.go
+++ b/yggdrasil.go
@@ -66,6 +66,9 @@ func generateConfig(isAutoconf bool) *nodeConfig {
 	cfg.IfName = defaults.GetDefaults().DefaultIfName
 	cfg.IfMTU = defaults.GetDefaults().DefaultIfMTU
 	cfg.IfTAPMode = defaults.GetDefaults().DefaultIfTAPMode
+	cfg.SessionFirewall.Enable = false
+	cfg.SessionFirewall.AllowFromDirect = true
+	cfg.SessionFirewall.AllowFromRemote = true
 
 	return &cfg
 }