diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3d30f098..0eec877a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@ New release of Oragono!
 ### Security
 
 ### Added
+* Added ability to `DLINE` IP addresses ad networks, to allow for fast blocking.
 
 ### Changed
 
diff --git a/irc/commands.go b/irc/commands.go
index 7ee7b63b..723bd668 100644
--- a/irc/commands.go
+++ b/irc/commands.go
@@ -76,6 +76,11 @@ var Commands = map[string]Command{
 		handler:   debugHandler,
 		minParams: 1,
 	},
+	"DLINE": {
+		handler:   dlineHandler,
+		minParams: 1,
+		oper:      true,
+	},
 	"HELP": {
 		handler:   helpHandler,
 		minParams: 0,
@@ -200,6 +205,11 @@ var Commands = map[string]Command{
 		handler:   topicHandler,
 		minParams: 1,
 	},
+	"UNDLINE": {
+		handler:   undlineHandler,
+		minParams: 1,
+		oper:      true,
+	},
 	"USER": {
 		handler:      userHandler,
 		usablePreReg: true,
diff --git a/irc/dline.go b/irc/dline.go
new file mode 100644
index 00000000..92ebbd59
--- /dev/null
+++ b/irc/dline.go
@@ -0,0 +1,151 @@
+// Copyright (c) 2016- Daniel Oaks <daniel@danieloaks.net>
+// released under the MIT license
+
+package irc
+
+import "net"
+import "time"
+
+// IPRestrictTime contains the expiration info about the given IP.
+type IPRestrictTime struct {
+	// Expires is when this block expires.
+	Expires time.Time
+	// Length is how long this block lasts for.
+	Length time.Duration
+}
+
+// IsExpired returns true if the time has expired.
+func (iptime *IPRestrictTime) IsExpired() bool {
+	return iptime.Expires.Before(time.Now())
+}
+
+// IPBanInfo holds info about an IP/net ban.
+type IPBanInfo struct {
+	// Reason is the ban reason.
+	Reason string
+	// OperReason is an oper ban reason.
+	OperReason string
+	// Time holds details about the duration, if it exists.
+	Time *IPRestrictTime
+}
+
+// dLineAddr contains the address itself and expiration time for a given network.
+type dLineAddr struct {
+	// Address is the address that is blocked.
+	Address net.IP
+	// Info contains information on the ban.
+	Info IPBanInfo
+}
+
+// dLineNet contains the net itself and expiration time for a given network.
+type dLineNet struct {
+	// Network is the network that is blocked.
+	Network net.IPNet
+	// Info contains information on the ban.
+	Info IPBanInfo
+}
+
+// DLineManager manages and dlines.
+type DLineManager struct {
+	// addresses that are dlined
+	addresses map[string]*dLineAddr
+	// networks that are dlined
+	networks map[string]*dLineNet
+}
+
+// NewDLineManager returns a new DLineManager.
+func NewDLineManager() *DLineManager {
+	dm := DLineManager{
+		addresses: make(map[string]*dLineAddr),
+		networks:  make(map[string]*dLineNet),
+	}
+	return &dm
+}
+
+// AddNetwork adds a network to the blocked list.
+func (dm *DLineManager) AddNetwork(network net.IPNet, length *IPRestrictTime) {
+	netString := network.String()
+	dln := dLineNet{
+		Network: network,
+		Info: IPBanInfo{
+			Time:       length,
+			Reason:     "",
+			OperReason: "",
+		},
+	}
+	dm.networks[netString] = &dln
+}
+
+// RemoveNetwork removes a network from the blocked list.
+func (dm *DLineManager) RemoveNetwork(network net.IPNet) {
+	netString := network.String()
+	delete(dm.networks, netString)
+}
+
+// AddIP adds an IP address to the blocked list.
+func (dm *DLineManager) AddIP(addr net.IP, length *IPRestrictTime) {
+	addrString := addr.String()
+	dla := dLineAddr{
+		Address: addr,
+		Info: IPBanInfo{
+			Time:       length,
+			Reason:     "",
+			OperReason: "",
+		},
+	}
+	dm.addresses[addrString] = &dla
+}
+
+// RemoveIP removes an IP from the blocked list.
+func (dm *DLineManager) RemoveIP(addr net.IP) {
+	addrString := addr.String()
+	delete(dm.addresses, addrString)
+}
+
+// CheckIP returns whether or not an IP address was banned, and how long it is banned for.
+func (dm *DLineManager) CheckIP(addr net.IP) (isBanned bool, info *IPBanInfo) {
+	// check IP addr
+	addrString := addr.String()
+
+	addrInfo := dm.addresses[addrString]
+	if addrInfo != nil {
+		if addrInfo.Info.Time != nil {
+			if addrInfo.Info.Time.IsExpired() {
+				// ban on IP has expired, remove it from our blocked list
+				dm.RemoveIP(addr)
+			} else {
+				return true, &addrInfo.Info
+			}
+		} else {
+			return true, nil
+		}
+	}
+
+	// check networks
+	var netsToRemove []net.IPNet
+
+	for _, netInfo := range dm.networks {
+		if !netInfo.Network.Contains(addr) {
+			continue
+		}
+
+		if netInfo.Info.Time != nil {
+			if netInfo.Info.Time.IsExpired() {
+				// ban on network has expired, remove it from our blocked list
+				netsToRemove = append(netsToRemove, netInfo.Network)
+			} else {
+				return true, &addrInfo.Info
+			}
+		} else {
+			return true, nil
+		}
+	}
+
+	// remove expired networks
+	for _, expiredNet := range netsToRemove {
+		dm.RemoveNetwork(expiredNet)
+	}
+
+	// no matches!
+	return false, nil
+}
diff --git a/irc/help.go b/irc/help.go
index d96b5405..371195fc 100644
--- a/irc/help.go
+++ b/irc/help.go
@@ -36,7 +36,8 @@ Oragono supports the following channel modes:
 
   +i  |  Invite-only mode, only invited clients can join the channel.
   +m  |  Moderated mode, only privileged clients can talk on the channel.
-  +n  |  No-outside-messages mode, only users that are on the channel can send the channel messages.
+  +n  |  No-outside-messages mode, only users that are on the channel can send
+      |  messages to it.
   +t  |  Only channel opers can modify the topic.
   +s  |  Secret mode, channel won't show up in /LIST or whois replies.
 
@@ -95,6 +96,26 @@ Prints debug information about the IRCd. <option> can be one of:
 * STARTCPUPROFILE: Starts the CPU profiler.
 * STOPCPUPROFILE: Stops the CPU profiler.
 * PROFILEHEAP: Writes out the CPU profiler info.`,
+	},
+	"dline": {
+		oper: true,
+		text: `DLINE [duration] <ip>/<net> [reason [| oper reason]]
+
+Bans an IP address or network from connecting to the server. If the duration is
+given then only for that long. The reason is shown to the user themselves, but
+everyone else will see a standard message. The oper reason is shown to
+operators getting info about the DLINEs that exist.
+
+Bans are saved across subsequent launches of the server.
+
+[duration] can be of the following forms:
+	10h 8m 13s
+
+<net> is specified in typical CIDR notation. For example:
+	127.0.0.1/8
+	8.8.8.8/24
+
+[reason] and [oper reason], if they exist, are separated by a vertical bar (|).`,
 	},
 	"help": {
 		text: `HELP <argument>
@@ -250,7 +271,7 @@ Indicates that you're leaving the server, and shows everyone the given reason.`,
 REG VERIFY <accountname> <auth_code>
 
 Used in account registration. See the relevant specs for more info:
-https://github.com/DanielOaks/ircv3-specifications/blob/register-and-verify/extensions/reg-core-3.3.md`,
+http://oragono.io/specs.html`,
 	},
 	"rehash": {
 		oper: true,
@@ -268,6 +289,16 @@ Shows the time of the current, or the given, server.`,
 
 If [topic] is given, sets the topic in the channel to that. If [topic] is not
 given, views the current topic on the channel.`,
+	},
+	"undline": {
+		oper: true,
+		text: `UNDLINE <ip>/<net>
+
+Removes an existing ban on an IP address or a network.
+
+<net> is specified in typical CIDR notation. For example:
+	127.0.0.1/8
+	8.8.8.8/24`,
 	},
 	"user": {
 		text: `USER <username> 0 * <realname>
@@ -316,8 +347,7 @@ Returns historical information on the last user with the given nickname.`,
 
 Oragono supports an experimental unicode casemapping designed for extended
 Unicode support. This casemapping is based off RFC 7700 and the draft rfc7700
-casemapping spec here:
-https://github.com/DanielOaks/ircv3-specifications/blob/master%2Brfc7700/documentation/rfc7700.md`,
+casemapping spec here: http://oragono.io/specs.html`,
 	},
 	"prefix": {
 		text: `RPL_ISUPPORT PREFIX
diff --git a/irc/server.go b/irc/server.go
index 4d3f9023..644395a1 100644
--- a/irc/server.go
+++ b/irc/server.go
@@ -29,6 +29,9 @@ var (
 	// cached because this may be used lots
 	tooManyClientsMsg      = ircmsg.MakeMessage(nil, "", "ERROR", "Too many clients from your IP or network")
 	tooManyClientsBytes, _ = tooManyClientsMsg.Line()
+
+	bannedFromServerMsg      = ircmsg.MakeMessage(nil, "", "ERROR", "You are banned from this server (%s)")
+	bannedFromServerBytes, _ = bannedFromServerMsg.Line()
 )
 
 // Limits holds the maximum limits for various things such as topic lengths
@@ -78,6 +81,7 @@ type Server struct {
 	connectionLimitsMutex sync.Mutex // used when affecting the connection limiter, to make sure rehashing doesn't make things go out-of-whack
 	ctime                 time.Time
 	currentOpers          map[*Client]bool
+	dlines                *DLineManager
 	idle                  chan *Client
 	isupport              *ISupportList
 	limits                Limits
@@ -190,6 +194,9 @@ func NewServer(configFilename string, config *Config) *Server {
 	}
 	server.store = *db
 
+	// load dlines
+	server.loadDLines()
+
 	// load password manager
 	err = server.store.View(func(tx *buntdb.Tx) error {
 		saltString, err := tx.Get(keySalt)
@@ -342,18 +349,33 @@ func (server *Server) Run() {
 			// check connection limits
 			ipaddr := net.ParseIP(IPString(conn.Conn.RemoteAddr()))
 			if ipaddr != nil {
+				// check DLINEs
+				isBanned, info := server.dlines.CheckIP(ipaddr)
+				if isBanned {
+					banMessage := fmt.Sprintf(bannedFromServerBytes, info.Reason)
+					if info.Time != nil {
+						banMessage += fmt.Sprintf(" [%s]", info.Time.Length.String())
+					}
+					conn.Conn.Write([]byte(banMessage))
+					conn.Conn.Close()
+					continue
+				}
+
+				// check connection limits
 				server.connectionLimitsMutex.Lock()
 				err := server.connectionLimits.AddClient(ipaddr, false)
 				server.connectionLimitsMutex.Unlock()
-				if err == nil {
-					go NewClient(server, conn.Conn, conn.IsTLS)
+				if err != nil {
+					// too many connections from one client, tell the client and close the connection
+					// this might not show up properly on some clients, but our objective here is just to close it out before it has a load impact on us
+					conn.Conn.Write([]byte(tooManyClientsBytes))
+					conn.Conn.Close()
 					continue
 				}
+
+				go NewClient(server, conn.Conn, conn.IsTLS)
+				continue
 			}
-			// too many connections from one client, tell the client and close the connection
-			// this might not show up properly on some clients, but our objective here is just to close it out before it has a load impact on us
-			conn.Conn.Write([]byte(tooManyClientsBytes))
-			conn.Conn.Close()
 
 		case client := <-server.idle:
 			client.Idle()