diff --git a/.github/workflows/clippy.yml b/.github/workflows/clippy.yml
index 7aa762352..452f62eeb 100644
--- a/.github/workflows/clippy.yml
+++ b/.github/workflows/clippy.yml
@@ -1,6 +1,6 @@
 on:
   push:
-    branches: [ staging, trying ]
+    branches: [staging, trying]
   pull_request_target:
 
 name: Clippy check
@@ -17,7 +17,7 @@ jobs:
       - uses: actions-rs/toolchain@v1
         with:
           profile: minimal
-          toolchain: 1.53.0
+          toolchain: nightly
           override: true
           components: clippy
       - uses: actions-rs/clippy-check@v1
diff --git a/.github/workflows/rustfmt.yaml b/.github/workflows/rustfmt.yaml
index 3d065a20e..d68863c41 100644
--- a/.github/workflows/rustfmt.yaml
+++ b/.github/workflows/rustfmt.yaml
@@ -1,6 +1,6 @@
 on:
   push:
-    branches: [ staging, trying ]
+    branches: [staging, trying]
   pull_request:
 
 name: Rustfmt check
@@ -11,7 +11,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions-rs/toolchain@v1
         with:
-          toolchain: stable
+          toolchain: nightly
           profile: minimal
           components: rustfmt
       - name: Check fmt
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 2b19a3889..09ad18279 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -1,6 +1,6 @@
 on:
   push:
-    branches: [ staging, trying ]
+    branches: [staging, trying]
   pull_request:
 
 name: Test
@@ -20,8 +20,8 @@ jobs:
         # Test on stable, MSRV 1.46, and nightly.
         # Failure is permitted on nightly.
         rust:
-          - stable
-          - 1.56.0
+          #- stable
+          #- 1.56.0
           - nightly
 
         features:
@@ -67,8 +67,8 @@ jobs:
         # Test on stable, MSRV 1.46, and nightly.
         # Failure is permitted on nightly.
         rust:
-          - stable
-          - 1.56.0
+          #- stable
+          #- 1.56.0
           - nightly
 
         features:
diff --git a/examples/dhcp_client.rs b/examples/dhcp_client.rs
index 456668e37..d220c3bc0 100644
--- a/examples/dhcp_client.rs
+++ b/examples/dhcp_client.rs
@@ -94,10 +94,7 @@ fn main() {
     }
 }
 
-fn set_ipv4_addr<DeviceT>(iface: &mut Interface<'_, DeviceT>, cidr: Ipv4Cidr)
-where
-    DeviceT: for<'d> Device<'d>,
-{
+fn set_ipv4_addr<DeviceT: Device>(iface: &mut Interface<'_, DeviceT>, cidr: Ipv4Cidr) {
     iface.update_ip_addrs(|addrs| {
         let dest = addrs.iter_mut().next().unwrap();
         *dest = IpCidr::Ipv4(cidr);
diff --git a/examples/utils.rs b/examples/utils.rs
index f82dd9a08..a98384098 100644
--- a/examples/utils.rs
+++ b/examples/utils.rs
@@ -159,7 +159,7 @@ pub fn parse_middleware_options<D>(
     loopback: bool,
 ) -> FaultInjector<Tracer<PcapWriter<D, Box<dyn io::Write>>>>
 where
-    D: for<'a> Device<'a>,
+    D: Device,
 {
     let drop_chance = matches
         .opt_str("drop-chance")
diff --git a/fuzz/utils.rs b/fuzz/utils.rs
index 89329d99d..206443420 100644
--- a/fuzz/utils.rs
+++ b/fuzz/utils.rs
@@ -93,7 +93,7 @@ pub fn parse_middleware_options<D>(
     loopback: bool,
 ) -> FaultInjector<Tracer<PcapWriter<D, Box<dyn Write>>>>
 where
-    D: for<'a> Device<'a>,
+    D: Device,
 {
     let drop_chance = matches
         .opt_str("drop-chance")
diff --git a/src/iface/interface.rs b/src/iface/interface.rs
index 50f9d0f99..b1c5b6b18 100644
--- a/src/iface/interface.rs
+++ b/src/iface/interface.rs
@@ -19,7 +19,7 @@ use crate::{Error, Result};
 /// The network interface logically owns a number of other data structures; to avoid
 /// a dependency on heap allocation, it instead owns a `BorrowMut<[T]>`, which can be
 /// a `&mut [T]`, or `Vec<T>` if a heap is available.
-pub struct Interface<'a, DeviceT: for<'d> Device<'d>> {
+pub struct Interface<'a, DeviceT: Device> {
     device: DeviceT,
     sockets: SocketSet<'a>,
     inner: InterfaceInner<'a>,
@@ -53,7 +53,7 @@ struct InterfaceInner<'a> {
 }
 
 /// A builder structure used for creating a network interface.
-pub struct InterfaceBuilder<'a, DeviceT: for<'d> Device<'d>> {
+pub struct InterfaceBuilder<'a, DeviceT: Device> {
     device: DeviceT,
     #[cfg(any(feature = "medium-ethernet", feature = "medium-ieee802154"))]
     hardware_addr: Option<HardwareAddress>,
@@ -73,10 +73,7 @@ pub struct InterfaceBuilder<'a, DeviceT: for<'d> Device<'d>> {
     ipv4_multicast_groups: ManagedMap<'a, Ipv4Address, ()>,
 }
 
-impl<'a, DeviceT> InterfaceBuilder<'a, DeviceT>
-where
-    DeviceT: for<'d> Device<'d>,
-{
+impl<'a, DeviceT: Device> InterfaceBuilder<'a, DeviceT> {
     /// Create a builder used for creating a network interface using the
     /// given device and address.
     #[cfg_attr(
@@ -465,10 +462,7 @@ enum IgmpReportState {
     },
 }
 
-impl<'a, DeviceT> Interface<'a, DeviceT>
-where
-    DeviceT: for<'d> Device<'d>,
-{
+impl<'a, DeviceT: Device> Interface<'a, DeviceT> {
     /// Add a socket to the interface, and return its handle.
     ///
     /// # Panics
diff --git a/src/lib.rs b/src/lib.rs
index b8653cf0b..e899ddd99 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -7,6 +7,7 @@
     ),
     deny(unused)
 )]
+#![feature(generic_associated_types)]
 
 //! The _smoltcp_ library is built in a layered structure, with the layers corresponding
 //! to the levels of API abstraction. Only the highest layers would be used by a typical
diff --git a/src/phy/fault_injector.rs b/src/phy/fault_injector.rs
index 6a83bf759..32edcd105 100644
--- a/src/phy/fault_injector.rs
+++ b/src/phy/fault_injector.rs
@@ -94,13 +94,13 @@ impl State {
 /// adverse network conditions (such as random packet loss or corruption), or software
 /// or hardware limitations (such as a limited number or size of usable network buffers).
 #[derive(Debug)]
-pub struct FaultInjector<D: for<'a> Device<'a>> {
+pub struct FaultInjector<D: Device> {
     inner: D,
     state: RefCell<State>,
     config: Config,
 }
 
-impl<D: for<'a> Device<'a>> FaultInjector<D> {
+impl<D: Device> FaultInjector<D> {
     /// Create a fault injector device, using the given random number generator seed.
     pub fn new(inner: D, seed: u32) -> FaultInjector<D> {
         let state = State {
@@ -195,12 +195,15 @@ impl<D: for<'a> Device<'a>> FaultInjector<D> {
     }
 }
 
-impl<'a, D> Device<'a> for FaultInjector<D>
-where
-    D: for<'b> Device<'b>,
-{
-    type RxToken = RxToken<'a, <D as Device<'a>>::RxToken>;
-    type TxToken = TxToken<'a, <D as Device<'a>>::TxToken>;
+impl<D: Device> Device for FaultInjector<D> {
+    type RxToken<'a>
+    where
+        Self: 'a,
+    = RxToken<'a, D::RxToken<'a>>;
+    type TxToken<'a>
+    where
+        Self: 'a,
+    = TxToken<'a, D::TxToken<'a>>;
 
     fn capabilities(&self) -> DeviceCapabilities {
         let mut caps = self.inner.capabilities();
@@ -210,7 +213,7 @@ where
         caps
     }
 
-    fn receive(&'a mut self) -> Option<(Self::RxToken, Self::TxToken)> {
+    fn receive(&mut self) -> Option<(Self::RxToken<'_>, Self::TxToken<'_>)> {
         let &mut Self {
             ref mut inner,
             ref state,
@@ -233,7 +236,7 @@ where
         })
     }
 
-    fn transmit(&'a mut self) -> Option<Self::TxToken> {
+    fn transmit(&mut self) -> Option<Self::TxToken<'_>> {
         let &mut Self {
             ref mut inner,
             ref state,
diff --git a/src/phy/fuzz_injector.rs b/src/phy/fuzz_injector.rs
index 4be1fc0e2..852f774de 100644
--- a/src/phy/fuzz_injector.rs
+++ b/src/phy/fuzz_injector.rs
@@ -19,14 +19,14 @@ pub trait Fuzzer {
 #[allow(unused)]
 #[derive(Debug)]
 #[cfg_attr(feature = "defmt", derive(defmt::Format))]
-pub struct FuzzInjector<D: for<'a> Device<'a>, FTx: Fuzzer, FRx: Fuzzer> {
+pub struct FuzzInjector<D: Device, FTx: Fuzzer, FRx: Fuzzer> {
     inner: D,
     fuzz_tx: FTx,
     fuzz_rx: FRx,
 }
 
 #[allow(unused)]
-impl<D: for<'a> Device<'a>, FTx: Fuzzer, FRx: Fuzzer> FuzzInjector<D, FTx, FRx> {
+impl<D: Device, FTx: Fuzzer, FRx: Fuzzer> FuzzInjector<D, FTx, FRx> {
     /// Create a fuzz injector device.
     pub fn new(inner: D, fuzz_tx: FTx, fuzz_rx: FRx) -> FuzzInjector<D, FTx, FRx> {
         FuzzInjector {
@@ -42,14 +42,19 @@ impl<D: for<'a> Device<'a>, FTx: Fuzzer, FRx: Fuzzer> FuzzInjector<D, FTx, FRx>
     }
 }
 
-impl<'a, D, FTx, FRx> Device<'a> for FuzzInjector<D, FTx, FRx>
+impl<D: Device, FTx, FRx> Device for FuzzInjector<D, FTx, FRx>
 where
-    D: for<'b> Device<'b>,
-    FTx: Fuzzer + 'a,
-    FRx: Fuzzer + 'a,
+    FTx: Fuzzer,
+    FRx: Fuzzer,
 {
-    type RxToken = RxToken<'a, <D as Device<'a>>::RxToken, FRx>;
-    type TxToken = TxToken<'a, <D as Device<'a>>::TxToken, FTx>;
+    type RxToken<'a>
+    where
+        Self: 'a,
+    = RxToken<'a, D::RxToken<'a>, FRx>;
+    type TxToken<'a>
+    where
+        Self: 'a,
+    = TxToken<'a, D::TxToken<'a>, FTx>;
 
     fn capabilities(&self) -> DeviceCapabilities {
         let mut caps = self.inner.capabilities();
@@ -59,7 +64,7 @@ where
         caps
     }
 
-    fn receive(&'a mut self) -> Option<(Self::RxToken, Self::TxToken)> {
+    fn receive(&mut self) -> Option<(Self::RxToken<'_>, Self::TxToken<'_>)> {
         let &mut Self {
             ref mut inner,
             ref fuzz_rx,
@@ -78,7 +83,7 @@ where
         })
     }
 
-    fn transmit(&'a mut self) -> Option<Self::TxToken> {
+    fn transmit(&mut self) -> Option<Self::TxToken<'_>> {
         let &mut Self {
             ref mut inner,
             fuzz_rx: _,
diff --git a/src/phy/loopback.rs b/src/phy/loopback.rs
index 9b39aed33..e6a317828 100644
--- a/src/phy/loopback.rs
+++ b/src/phy/loopback.rs
@@ -29,9 +29,9 @@ impl Loopback {
     }
 }
 
-impl<'a> Device<'a> for Loopback {
-    type RxToken = RxToken;
-    type TxToken = TxToken<'a>;
+impl Device for Loopback {
+    type RxToken<'a> = RxToken;
+    type TxToken<'a> = TxToken<'a>;
 
     fn capabilities(&self) -> DeviceCapabilities {
         DeviceCapabilities {
@@ -41,7 +41,7 @@ impl<'a> Device<'a> for Loopback {
         }
     }
 
-    fn receive(&'a mut self) -> Option<(Self::RxToken, Self::TxToken)> {
+    fn receive(&mut self) -> Option<(Self::RxToken<'_>, Self::TxToken<'_>)> {
         self.queue.pop_front().map(move |buffer| {
             let rx = RxToken { buffer };
             let tx = TxToken {
@@ -51,7 +51,7 @@ impl<'a> Device<'a> for Loopback {
         })
     }
 
-    fn transmit(&'a mut self) -> Option<Self::TxToken> {
+    fn transmit(&mut self) -> Option<Self::TxToken<'_>> {
         Some(TxToken {
             queue: &mut self.queue,
         })
diff --git a/src/phy/mod.rs b/src/phy/mod.rs
index ae4a11819..8e12df99d 100644
--- a/src/phy/mod.rs
+++ b/src/phy/mod.rs
@@ -20,6 +20,8 @@ An implementation of the [Device](trait.Device.html) trait for a simple hardware
 Ethernet controller could look as follows:
 
 ```rust
+# #![feature(generic_associated_types)]
+
 use smoltcp::Result;
 use smoltcp::phy::{self, DeviceCapabilities, Device, Medium};
 use smoltcp::time::Instant;
@@ -38,16 +40,16 @@ impl<'a> StmPhy {
     }
 }
 
-impl<'a> phy::Device<'a> for StmPhy {
-    type RxToken = StmPhyRxToken<'a>;
-    type TxToken = StmPhyTxToken<'a>;
+impl phy::Device for StmPhy {
+    type RxToken<'a> where Self: 'a = StmPhyRxToken<'a>;
+    type TxToken<'a> where Self: 'a = StmPhyTxToken<'a>;
 
-    fn receive(&'a mut self) -> Option<(Self::RxToken, Self::TxToken)> {
+    fn receive(&mut self) -> Option<(Self::RxToken<'_>, Self::TxToken<'_>)> {
         Some((StmPhyRxToken(&mut self.rx_buffer[..]),
               StmPhyTxToken(&mut self.tx_buffer[..])))
     }
 
-    fn transmit(&'a mut self) -> Option<Self::TxToken> {
+    fn transmit(&mut self) -> Option<Self::TxToken<'_>> {
         Some(StmPhyTxToken(&mut self.tx_buffer[..]))
     }
 
@@ -312,9 +314,13 @@ impl Default for Medium {
 /// The interface is based on _tokens_, which are types that allow to receive/transmit a
 /// single packet. The `receive` and `transmit` functions only construct such tokens, the
 /// real sending/receiving operation are performed when the tokens are consumed.
-pub trait Device<'a> {
-    type RxToken: RxToken + 'a;
-    type TxToken: TxToken + 'a;
+pub trait Device {
+    type RxToken<'a>: RxToken
+    where
+        Self: 'a;
+    type TxToken<'a>: TxToken
+    where
+        Self: 'a;
 
     /// Construct a token pair consisting of one receive token and one transmit token.
     ///
@@ -322,10 +328,10 @@ pub trait Device<'a> {
     /// on the contents of the received packet. For example, this makes it possible to
     /// handle arbitrarily large ICMP echo ("ping") requests, where the all received bytes
     /// need to be sent back, without heap allocation.
-    fn receive(&'a mut self) -> Option<(Self::RxToken, Self::TxToken)>;
+    fn receive(&mut self) -> Option<(Self::RxToken<'_>, Self::TxToken<'_>)>;
 
     /// Construct a transmit token.
-    fn transmit(&'a mut self) -> Option<Self::TxToken>;
+    fn transmit(&mut self) -> Option<Self::TxToken<'_>>;
 
     /// Get a description of device capabilities.
     fn capabilities(&self) -> DeviceCapabilities;
diff --git a/src/phy/pcap_writer.rs b/src/phy/pcap_writer.rs
index 069e55503..2acf3e489 100644
--- a/src/phy/pcap_writer.rs
+++ b/src/phy/pcap_writer.rs
@@ -118,7 +118,7 @@ impl<T: Write> PcapSink for T {
 #[derive(Debug)]
 pub struct PcapWriter<D, S>
 where
-    D: for<'a> Device<'a>,
+    D: Device,
     S: PcapSink,
 {
     lower: D,
@@ -126,7 +126,7 @@ where
     mode: PcapMode,
 }
 
-impl<D: for<'a> Device<'a>, S: PcapSink> PcapWriter<D, S> {
+impl<D: Device, S: PcapSink> PcapWriter<D, S> {
     /// Creates a packet capture writer.
     pub fn new(lower: D, mut sink: S, mode: PcapMode) -> PcapWriter<D, S> {
         let medium = lower.capabilities().medium;
@@ -162,19 +162,24 @@ impl<D: for<'a> Device<'a>, S: PcapSink> PcapWriter<D, S> {
     }
 }
 
-impl<'a, D, S> Device<'a> for PcapWriter<D, S>
+impl<D: Device, S> Device for PcapWriter<D, S>
 where
-    D: for<'b> Device<'b>,
-    S: PcapSink + 'a,
+    S: PcapSink,
 {
-    type RxToken = RxToken<'a, <D as Device<'a>>::RxToken, S>;
-    type TxToken = TxToken<'a, <D as Device<'a>>::TxToken, S>;
+    type RxToken<'a>
+    where
+        Self: 'a,
+    = RxToken<'a, D::RxToken<'a>, S>;
+    type TxToken<'a>
+    where
+        Self: 'a,
+    = TxToken<'a, D::TxToken<'a>, S>;
 
     fn capabilities(&self) -> DeviceCapabilities {
         self.lower.capabilities()
     }
 
-    fn receive(&'a mut self) -> Option<(Self::RxToken, Self::TxToken)> {
+    fn receive(&mut self) -> Option<(Self::RxToken<'_>, Self::TxToken<'_>)> {
         let sink = &self.sink;
         let mode = self.mode;
         self.lower.receive().map(move |(rx_token, tx_token)| {
@@ -192,7 +197,7 @@ where
         })
     }
 
-    fn transmit(&'a mut self) -> Option<Self::TxToken> {
+    fn transmit(&mut self) -> Option<Self::TxToken<'_>> {
         let sink = &self.sink;
         let mode = self.mode;
         self.lower
diff --git a/src/phy/raw_socket.rs b/src/phy/raw_socket.rs
index e01438f46..2f4cb09da 100644
--- a/src/phy/raw_socket.rs
+++ b/src/phy/raw_socket.rs
@@ -48,9 +48,15 @@ impl RawSocket {
     }
 }
 
-impl<'a> Device<'a> for RawSocket {
-    type RxToken = RxToken;
-    type TxToken = TxToken;
+impl Device for RawSocket {
+    type RxToken<'a>
+    where
+        Self: 'a,
+    = RxToken;
+    type TxToken<'a>
+    where
+        Self: 'a,
+    = TxToken;
 
     fn capabilities(&self) -> DeviceCapabilities {
         DeviceCapabilities {
@@ -60,7 +66,7 @@ impl<'a> Device<'a> for RawSocket {
         }
     }
 
-    fn receive(&'a mut self) -> Option<(Self::RxToken, Self::TxToken)> {
+    fn receive(&mut self) -> Option<(Self::RxToken<'_>, Self::TxToken<'_>)> {
         let mut lower = self.lower.borrow_mut();
         let mut buffer = vec![0; self.mtu];
         match lower.recv(&mut buffer[..]) {
@@ -77,7 +83,7 @@ impl<'a> Device<'a> for RawSocket {
         }
     }
 
-    fn transmit(&'a mut self) -> Option<Self::TxToken> {
+    fn transmit(&mut self) -> Option<Self::TxToken<'_>> {
         Some(TxToken {
             lower: self.lower.clone(),
         })
diff --git a/src/phy/tracer.rs b/src/phy/tracer.rs
index fdf5b1cfc..3d0bca92f 100644
--- a/src/phy/tracer.rs
+++ b/src/phy/tracer.rs
@@ -12,12 +12,12 @@ use crate::{
 /// A tracer is a device that pretty prints all packets traversing it
 /// using the provided writer function, and then passes them to another
 /// device.
-pub struct Tracer<D: for<'a> Device<'a>> {
+pub struct Tracer<D: Device> {
     inner: D,
     writer: fn(Instant, Packet),
 }
 
-impl<D: for<'a> Device<'a>> Tracer<D> {
+impl<D: Device> Tracer<D> {
     /// Create a tracer device.
     pub fn new(inner: D, writer: fn(timestamp: Instant, packet: Packet)) -> Tracer<D> {
         Tracer { inner, writer }
@@ -44,18 +44,21 @@ impl<D: for<'a> Device<'a>> Tracer<D> {
     }
 }
 
-impl<'a, D> Device<'a> for Tracer<D>
-where
-    D: for<'b> Device<'b>,
-{
-    type RxToken = RxToken<<D as Device<'a>>::RxToken>;
-    type TxToken = TxToken<<D as Device<'a>>::TxToken>;
+impl<D: Device> Device for Tracer<D> {
+    type RxToken<'a>
+    where
+        Self: 'a,
+    = RxToken<D::RxToken<'a>>;
+    type TxToken<'a>
+    where
+        Self: 'a,
+    = TxToken<D::TxToken<'a>>;
 
     fn capabilities(&self) -> DeviceCapabilities {
         self.inner.capabilities()
     }
 
-    fn receive(&'a mut self) -> Option<(Self::RxToken, Self::TxToken)> {
+    fn receive(&mut self) -> Option<(Self::RxToken<'_>, Self::TxToken<'_>)> {
         let &mut Self {
             ref mut inner,
             writer,
@@ -77,7 +80,7 @@ where
         })
     }
 
-    fn transmit(&'a mut self) -> Option<Self::TxToken> {
+    fn transmit(&mut self) -> Option<Self::TxToken<'_>> {
         let &mut Self {
             ref mut inner,
             writer,
diff --git a/src/phy/tuntap_interface.rs b/src/phy/tuntap_interface.rs
index 6792a7be5..7bc2aa0d9 100644
--- a/src/phy/tuntap_interface.rs
+++ b/src/phy/tuntap_interface.rs
@@ -40,9 +40,9 @@ impl TunTapInterface {
     }
 }
 
-impl<'a> Device<'a> for TunTapInterface {
-    type RxToken = RxToken;
-    type TxToken = TxToken;
+impl Device for TunTapInterface {
+    type RxToken<'a> = RxToken;
+    type TxToken<'a> = TxToken;
 
     fn capabilities(&self) -> DeviceCapabilities {
         DeviceCapabilities {
@@ -52,7 +52,7 @@ impl<'a> Device<'a> for TunTapInterface {
         }
     }
 
-    fn receive(&'a mut self) -> Option<(Self::RxToken, Self::TxToken)> {
+    fn receive(&mut self) -> Option<(Self::RxToken<'_>, Self::TxToken<'_>)> {
         let mut lower = self.lower.borrow_mut();
         let mut buffer = vec![0; self.mtu];
         match lower.recv(&mut buffer[..]) {
@@ -69,7 +69,7 @@ impl<'a> Device<'a> for TunTapInterface {
         }
     }
 
-    fn transmit(&'a mut self) -> Option<Self::TxToken> {
+    fn transmit(&mut self) -> Option<Self::TxToken<'_>> {
         Some(TxToken {
             lower: self.lower.clone(),
         })