diff --git a/examples/benchmark.rs b/examples/benchmark.rs
index 9f908987..b0cedcfb 100644
--- a/examples/benchmark.rs
+++ b/examples/benchmark.rs
@@ -88,11 +88,14 @@ fn main() {
     let tcp2_tx_buffer = tcp::SocketBuffer::new(vec![0; 65535]);
     let tcp2_socket = tcp::Socket::new(tcp2_rx_buffer, tcp2_tx_buffer);
 
-    let mut config = Config::new();
+    let mut config = match device.capabilities().medium {
+        Medium::Ethernet => {
+            Config::new(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into())
+        }
+        Medium::Ip => Config::new(smoltcp::wire::HardwareAddress::Ip),
+        Medium::Ieee802154 => todo!(),
+    };
     config.random_seed = rand::random();
-    if device.capabilities().medium == Medium::Ethernet {
-        config.hardware_addr = Some(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into());
-    }
 
     let mut iface = Interface::new(config, &mut device);
     iface.update_ip_addrs(|ip_addrs| {
diff --git a/examples/client.rs b/examples/client.rs
index 8543ae06..5422aded 100644
--- a/examples/client.rs
+++ b/examples/client.rs
@@ -29,11 +29,14 @@ fn main() {
     let port = u16::from_str(&matches.free[1]).expect("invalid port format");
 
     // Create interface
-    let mut config = Config::new();
+    let mut config = match device.capabilities().medium {
+        Medium::Ethernet => {
+            Config::new(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into())
+        }
+        Medium::Ip => Config::new(smoltcp::wire::HardwareAddress::Ip),
+        Medium::Ieee802154 => todo!(),
+    };
     config.random_seed = rand::random();
-    if device.capabilities().medium == Medium::Ethernet {
-        config.hardware_addr = Some(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into());
-    }
 
     let mut iface = Interface::new(config, &mut device);
     iface.update_ip_addrs(|ip_addrs| {
diff --git a/examples/dhcp_client.rs b/examples/dhcp_client.rs
index 96654241..d118219d 100644
--- a/examples/dhcp_client.rs
+++ b/examples/dhcp_client.rs
@@ -28,11 +28,14 @@ fn main() {
         utils::parse_middleware_options(&mut matches, device, /*loopback=*/ false);
 
     // Create interface
-    let mut config = Config::new();
+    let mut config = match device.capabilities().medium {
+        Medium::Ethernet => {
+            Config::new(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into())
+        }
+        Medium::Ip => Config::new(smoltcp::wire::HardwareAddress::Ip),
+        Medium::Ieee802154 => todo!(),
+    };
     config.random_seed = rand::random();
-    if device.capabilities().medium == Medium::Ethernet {
-        config.hardware_addr = Some(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into());
-    }
     let mut iface = Interface::new(config, &mut device);
 
     // Create sockets
diff --git a/examples/dns.rs b/examples/dns.rs
index 8bf8b2c8..da066aaf 100644
--- a/examples/dns.rs
+++ b/examples/dns.rs
@@ -24,11 +24,14 @@ fn main() {
     let name = &matches.free[0];
 
     // Create interface
-    let mut config = Config::new();
+    let mut config = match device.capabilities().medium {
+        Medium::Ethernet => {
+            Config::new(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into())
+        }
+        Medium::Ip => Config::new(smoltcp::wire::HardwareAddress::Ip),
+        Medium::Ieee802154 => todo!(),
+    };
     config.random_seed = rand::random();
-    if device.capabilities().medium == Medium::Ethernet {
-        config.hardware_addr = Some(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into());
-    }
 
     let mut iface = Interface::new(config, &mut device);
     iface.update_ip_addrs(|ip_addrs| {
diff --git a/examples/httpclient.rs b/examples/httpclient.rs
index 1e5a2186..751916da 100644
--- a/examples/httpclient.rs
+++ b/examples/httpclient.rs
@@ -29,11 +29,14 @@ fn main() {
     let url = Url::parse(&matches.free[1]).expect("invalid url format");
 
     // Create interface
-    let mut config = Config::new();
+    let mut config = match device.capabilities().medium {
+        Medium::Ethernet => {
+            Config::new(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into())
+        }
+        Medium::Ip => Config::new(smoltcp::wire::HardwareAddress::Ip),
+        Medium::Ieee802154 => todo!(),
+    };
     config.random_seed = rand::random();
-    if device.capabilities().medium == Medium::Ethernet {
-        config.hardware_addr = Some(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into());
-    }
 
     let mut iface = Interface::new(config, &mut device);
     iface.update_ip_addrs(|ip_addrs| {
diff --git a/examples/loopback.rs b/examples/loopback.rs
index 1a4dee88..9bca85e5 100644
--- a/examples/loopback.rs
+++ b/examples/loopback.rs
@@ -10,7 +10,7 @@ use core::str;
 use log::{debug, error, info};
 
 use smoltcp::iface::{Config, Interface, SocketSet};
-use smoltcp::phy::{Loopback, Medium};
+use smoltcp::phy::{Device, Loopback, Medium};
 use smoltcp::socket::tcp;
 use smoltcp::time::{Duration, Instant};
 use smoltcp::wire::{EthernetAddress, IpAddress, IpCidr};
@@ -83,8 +83,13 @@ fn main() {
     };
 
     // Create interface
-    let mut config = Config::new();
-    config.hardware_addr = Some(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into());
+    let mut config = match device.capabilities().medium {
+        Medium::Ethernet => {
+            Config::new(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into())
+        }
+        Medium::Ip => Config::new(smoltcp::wire::HardwareAddress::Ip),
+        Medium::Ieee802154 => todo!(),
+    };
 
     let mut iface = Interface::new(config, &mut device);
     iface.update_ip_addrs(|ip_addrs| {
diff --git a/examples/multicast.rs b/examples/multicast.rs
index 639fa432..ec7ff435 100644
--- a/examples/multicast.rs
+++ b/examples/multicast.rs
@@ -28,11 +28,14 @@ fn main() {
         utils::parse_middleware_options(&mut matches, device, /*loopback=*/ false);
 
     // Create interface
-    let mut config = Config::new();
+    let mut config = match device.capabilities().medium {
+        Medium::Ethernet => {
+            Config::new(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into())
+        }
+        Medium::Ip => Config::new(smoltcp::wire::HardwareAddress::Ip),
+        Medium::Ieee802154 => todo!(),
+    };
     config.random_seed = rand::random();
-    if device.capabilities().medium == Medium::Ethernet {
-        config.hardware_addr = Some(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into());
-    }
 
     let mut iface = Interface::new(config, &mut device);
     iface.update_ip_addrs(|ip_addrs| {
diff --git a/examples/ping.rs b/examples/ping.rs
index beac5625..7e6cbdb0 100644
--- a/examples/ping.rs
+++ b/examples/ping.rs
@@ -105,11 +105,14 @@ fn main() {
     );
 
     // Create interface
-    let mut config = Config::new();
+    let mut config = match device.capabilities().medium {
+        Medium::Ethernet => {
+            Config::new(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into())
+        }
+        Medium::Ip => Config::new(smoltcp::wire::HardwareAddress::Ip),
+        Medium::Ieee802154 => todo!(),
+    };
     config.random_seed = rand::random();
-    if device.capabilities().medium == Medium::Ethernet {
-        config.hardware_addr = Some(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into());
-    }
 
     let mut iface = Interface::new(config, &mut device);
     iface.update_ip_addrs(|ip_addrs| {
diff --git a/examples/server.rs b/examples/server.rs
index f2bbc803..67df6392 100644
--- a/examples/server.rs
+++ b/examples/server.rs
@@ -24,11 +24,15 @@ fn main() {
         utils::parse_middleware_options(&mut matches, device, /*loopback=*/ false);
 
     // Create interface
-    let mut config = Config::new();
+    let mut config = match device.capabilities().medium {
+        Medium::Ethernet => {
+            Config::new(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into())
+        }
+        Medium::Ip => Config::new(smoltcp::wire::HardwareAddress::Ip),
+        Medium::Ieee802154 => todo!(),
+    };
+
     config.random_seed = rand::random();
-    if device.capabilities().medium == Medium::Ethernet {
-        config.hardware_addr = Some(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into());
-    }
 
     let mut iface = Interface::new(config, &mut device);
     iface.update_ip_addrs(|ip_addrs| {
diff --git a/examples/sixlowpan.rs b/examples/sixlowpan.rs
index 964a8562..5b41116c 100644
--- a/examples/sixlowpan.rs
+++ b/examples/sixlowpan.rs
@@ -47,11 +47,11 @@ use std::os::unix::io::AsRawFd;
 use std::str;
 
 use smoltcp::iface::{Config, Interface, SocketSet};
-use smoltcp::phy::{wait as phy_wait, Medium, RawSocket};
+use smoltcp::phy::{wait as phy_wait, Device, Medium, RawSocket};
 use smoltcp::socket::tcp;
 use smoltcp::socket::udp;
 use smoltcp::time::Instant;
-use smoltcp::wire::{Ieee802154Address, Ieee802154Pan, IpAddress, IpCidr};
+use smoltcp::wire::{EthernetAddress, Ieee802154Address, Ieee802154Pan, IpAddress, IpCidr};
 
 fn main() {
     utils::setup_logging("");
@@ -67,10 +67,16 @@ fn main() {
         utils::parse_middleware_options(&mut matches, device, /*loopback=*/ false);
 
     // Create interface
-    let mut config = Config::new();
+    let mut config = match device.capabilities().medium {
+        Medium::Ethernet => {
+            Config::new(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into())
+        }
+        Medium::Ip => Config::new(smoltcp::wire::HardwareAddress::Ip),
+        Medium::Ieee802154 => Config::new(
+            Ieee802154Address::Extended([0x1a, 0x0b, 0x42, 0x42, 0x42, 0x42, 0x42, 0x42]).into(),
+        ),
+    };
     config.random_seed = rand::random();
-    config.hardware_addr =
-        Some(Ieee802154Address::Extended([0x1a, 0x0b, 0x42, 0x42, 0x42, 0x42, 0x42, 0x42]).into());
     config.pan_id = Some(Ieee802154Pan(0xbeef));
 
     let mut iface = Interface::new(config, &mut device);
diff --git a/examples/sixlowpan_benchmark.rs b/examples/sixlowpan_benchmark.rs
index 8b9cf842..a389ca94 100644
--- a/examples/sixlowpan_benchmark.rs
+++ b/examples/sixlowpan_benchmark.rs
@@ -47,9 +47,9 @@ use std::os::unix::io::AsRawFd;
 use std::str;
 
 use smoltcp::iface::{Config, Interface, SocketSet};
-use smoltcp::phy::{wait as phy_wait, Medium, RawSocket};
+use smoltcp::phy::{wait as phy_wait, Device, Medium, RawSocket};
 use smoltcp::socket::tcp;
-use smoltcp::wire::{Ieee802154Address, Ieee802154Pan, IpAddress, IpCidr};
+use smoltcp::wire::{EthernetAddress, Ieee802154Address, Ieee802154Pan, IpAddress, IpCidr};
 
 //For benchmark
 use smoltcp::time::{Duration, Instant};
@@ -147,10 +147,16 @@ fn main() {
     };
 
     // Create interface
-    let mut config = Config::new();
+    let mut config = match device.capabilities().medium {
+        Medium::Ethernet => {
+            Config::new(EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]).into())
+        }
+        Medium::Ip => Config::new(smoltcp::wire::HardwareAddress::Ip),
+        Medium::Ieee802154 => Config::new(
+            Ieee802154Address::Extended([0x1a, 0x0b, 0x42, 0x42, 0x42, 0x42, 0x42, 0x42]).into(),
+        ),
+    };
     config.random_seed = rand::random();
-    config.hardware_addr =
-        Some(Ieee802154Address::Extended([0x1a, 0x0b, 0x42, 0x42, 0x42, 0x42, 0x42, 0x42]).into());
     config.pan_id = Some(Ieee802154Pan(0xbeef));
 
     let mut iface = Interface::new(config, &mut device);
diff --git a/src/iface/interface/ethernet.rs b/src/iface/interface/ethernet.rs
index b769909c..bf8496fe 100644
--- a/src/iface/interface/ethernet.rs
+++ b/src/iface/interface/ethernet.rs
@@ -22,7 +22,7 @@ impl InterfaceInner {
         // Ignore any packets not directed to our hardware address or any of the multicast groups.
         if !eth_frame.dst_addr().is_broadcast()
             && !eth_frame.dst_addr().is_multicast()
-            && HardwareAddress::Ethernet(eth_frame.dst_addr()) != self.hardware_addr.unwrap()
+            && HardwareAddress::Ethernet(eth_frame.dst_addr()) != self.hardware_addr
         {
             return None;
         }
@@ -64,7 +64,7 @@ impl InterfaceInner {
             debug_assert!(tx_buffer.as_ref().len() == tx_len);
             let mut frame = EthernetFrame::new_unchecked(tx_buffer);
 
-            let src_addr = self.hardware_addr.unwrap().ethernet_or_panic();
+            let src_addr = self.hardware_addr.ethernet_or_panic();
             frame.set_src_addr(src_addr);
 
             f(frame);
diff --git a/src/iface/interface/ieee802154.rs b/src/iface/interface/ieee802154.rs
index 19faed79..78023001 100644
--- a/src/iface/interface/ieee802154.rs
+++ b/src/iface/interface/ieee802154.rs
@@ -44,7 +44,7 @@ impl InterfaceInner {
         packet: IpPacket,
         frag: &mut Fragmenter,
     ) {
-        let ll_src_a = self.hardware_addr.unwrap().ieee802154_or_panic();
+        let ll_src_a = self.hardware_addr.ieee802154_or_panic();
 
         // Create the IEEE802.15.4 header.
         let ieee_repr = Ieee802154Repr {
diff --git a/src/iface/interface/ipv4.rs b/src/iface/interface/ipv4.rs
index bd1d6e1d..50aff283 100644
--- a/src/iface/interface/ipv4.rs
+++ b/src/iface/interface/ipv4.rs
@@ -74,7 +74,9 @@ impl InterfaceInner {
 
         #[cfg(feature = "socket-dhcpv4")]
         {
-            if ipv4_repr.next_header == IpProtocol::Udp && self.hardware_addr.is_some() {
+            if ipv4_repr.next_header == IpProtocol::Udp
+                && matches!(self.caps.medium, Medium::Ethernet)
+            {
                 let udp_packet = check!(UdpPacket::new_checked(ip_payload));
                 if let Some(dhcp_socket) = sockets
                     .items_mut()
@@ -206,17 +208,14 @@ impl InterfaceInner {
                 // We fill from requests too because if someone is requesting our address they
                 // are probably going to talk to us, so we avoid having to request their address
                 // when we later reply to them.
-                self.neighbor_cache.as_mut().unwrap().fill(
+                self.neighbor_cache.fill(
                     source_protocol_addr.into(),
                     source_hardware_addr.into(),
                     timestamp,
                 );
 
                 if operation == ArpOperation::Request {
-                    let src_hardware_addr = match self.hardware_addr {
-                        Some(HardwareAddress::Ethernet(addr)) => addr,
-                        _ => unreachable!(),
-                    };
+                    let src_hardware_addr = self.hardware_addr.ethernet_or_panic();
 
                     Some(EthernetPacket::Arp(ArpRepr::EthernetIpv4 {
                         operation: ArpOperation::Reply,
@@ -352,7 +351,7 @@ impl InterfaceInner {
         let emit_ethernet = |repr: &IpRepr, tx_buffer: &mut [u8]| {
             let mut frame = EthernetFrame::new_unchecked(tx_buffer);
 
-            let src_addr = self.hardware_addr.unwrap().ethernet_or_panic();
+            let src_addr = self.hardware_addr.ethernet_or_panic();
             frame.set_src_addr(src_addr);
             frame.set_dst_addr(frag.ipv4.dst_hardware_addr);
 
diff --git a/src/iface/interface/ipv6.rs b/src/iface/interface/ipv6.rs
index 220ee13b..c57e0691 100644
--- a/src/iface/interface/ipv6.rs
+++ b/src/iface/interface/ipv6.rs
@@ -192,17 +192,9 @@ impl InterfaceInner {
                         return None;
                     }
                     if flags.contains(NdiscNeighborFlags::OVERRIDE)
-                        || !self
-                            .neighbor_cache
-                            .as_mut()
-                            .unwrap()
-                            .lookup(&ip_addr, self.now)
-                            .found()
+                        || !self.neighbor_cache.lookup(&ip_addr, self.now).found()
                     {
-                        self.neighbor_cache
-                            .as_mut()
-                            .unwrap()
-                            .fill(ip_addr, lladdr, self.now)
+                        self.neighbor_cache.fill(ip_addr, lladdr, self.now)
                     }
                 }
                 None
@@ -217,11 +209,8 @@ impl InterfaceInner {
                     if !lladdr.is_unicast() || !target_addr.is_unicast() {
                         return None;
                     }
-                    self.neighbor_cache.as_mut().unwrap().fill(
-                        ip_repr.src_addr.into(),
-                        lladdr,
-                        self.now,
-                    );
+                    self.neighbor_cache
+                        .fill(ip_repr.src_addr.into(), lladdr, self.now);
                 }
 
                 if self.has_solicited_node(ip_repr.dst_addr) && self.has_ip_addr(target_addr) {
@@ -229,7 +218,7 @@ impl InterfaceInner {
                         flags: NdiscNeighborFlags::SOLICITED,
                         target_addr,
                         #[cfg(any(feature = "medium-ethernet", feature = "medium-ieee802154"))]
-                        lladdr: Some(self.hardware_addr.unwrap().into()),
+                        lladdr: Some(self.hardware_addr.into()),
                     });
                     let ip_repr = Ipv6Repr {
                         src_addr: target_addr,
diff --git a/src/iface/interface/mod.rs b/src/iface/interface/mod.rs
index 7ab5b553..34ad4bd2 100644
--- a/src/iface/interface/mod.rs
+++ b/src/iface/interface/mod.rs
@@ -240,9 +240,8 @@ pub struct InterfaceInner {
     rand: Rand,
 
     #[cfg(any(feature = "medium-ethernet", feature = "medium-ieee802154"))]
-    neighbor_cache: Option<NeighborCache>,
-    #[cfg(any(feature = "medium-ethernet", feature = "medium-ieee802154"))]
-    hardware_addr: Option<HardwareAddress>,
+    neighbor_cache: NeighborCache,
+    hardware_addr: HardwareAddress,
     #[cfg(feature = "medium-ieee802154")]
     sequence_no: u8,
     #[cfg(feature = "medium-ieee802154")]
@@ -280,8 +279,7 @@ pub struct Config {
     ///
     /// # Panics
     /// Creating the interface panics if the address is not unicast.
-    #[cfg(any(feature = "medium-ethernet", feature = "medium-ieee802154"))]
-    pub hardware_addr: Option<HardwareAddress>,
+    pub hardware_addr: HardwareAddress,
 
     /// Set the IEEE802.15.4 PAN ID the interface will use.
     ///
@@ -291,23 +289,16 @@ pub struct Config {
 }
 
 impl Config {
-    pub fn new() -> Self {
+    pub fn new(hardware_addr: HardwareAddress) -> Self {
         Config {
             random_seed: 0,
-            #[cfg(any(feature = "medium-ethernet", feature = "medium-ieee802154"))]
-            hardware_addr: None,
+            hardware_addr,
             #[cfg(feature = "medium-ieee802154")]
             pan_id: None,
         }
     }
 }
 
-impl Default for Config {
-    fn default() -> Self {
-        Self::new()
-    }
-}
-
 #[derive(Debug, PartialEq)]
 #[cfg_attr(feature = "defmt", derive(defmt::Format))]
 #[cfg(feature = "medium-ethernet")]
@@ -476,29 +467,11 @@ impl Interface {
     {
         let caps = device.capabilities();
 
-        #[cfg(any(feature = "medium-ethernet", feature = "medium-ieee802154"))]
-        let hardware_addr = match caps.medium {
-            #[cfg(feature = "medium-ethernet")]
-            Medium::Ethernet => Some(
-                config
-                    .hardware_addr
-                    .expect("hardware_addr required option was not set"),
-            ),
-            #[cfg(feature = "medium-ip")]
-            Medium::Ip => {
-                assert!(
-                    config.hardware_addr.is_none(),
-                    "hardware_addr is set, but device medium is IP"
-                );
-                None
-            }
-            #[cfg(feature = "medium-ieee802154")]
-            Medium::Ieee802154 => Some(
-                config
-                    .hardware_addr
-                    .expect("hardware_addr required option was not set"),
-            ),
-        };
+        assert_eq!(
+            config.hardware_addr.medium(),
+            caps.medium,
+            "The hardware address does not match the medium of the interface."
+        );
 
         let mut rand = Rand::new(config.random_seed);
 
@@ -548,14 +521,13 @@ impl Interface {
             inner: InterfaceInner {
                 now: Instant::from_secs(0),
                 caps,
-                #[cfg(any(feature = "medium-ethernet", feature = "medium-ieee802154"))]
-                hardware_addr,
+                hardware_addr: config.hardware_addr,
                 ip_addrs: Vec::new(),
                 #[cfg(feature = "proto-ipv4")]
                 any_ip: false,
                 routes: Routes::new(),
                 #[cfg(any(feature = "medium-ethernet", feature = "medium-ieee802154"))]
-                neighbor_cache: Some(NeighborCache::new()),
+                neighbor_cache: NeighborCache::new(),
                 #[cfg(feature = "proto-igmp")]
                 ipv4_multicast_groups: LinearMap::new(),
                 #[cfg(feature = "proto-igmp")]
@@ -599,7 +571,7 @@ impl Interface {
                 || self.inner.caps.medium == Medium::Ieee802154
         );
 
-        self.inner.hardware_addr.unwrap()
+        self.inner.hardware_addr
     }
 
     /// Set the HardwareAddress address of the interface.
@@ -621,7 +593,7 @@ impl Interface {
         );
 
         InterfaceInner::check_hardware_addr(&addr);
-        self.inner.hardware_addr = Some(addr);
+        self.inner.hardware_addr = addr;
     }
 
     /// Get the IP addresses of the interface.
@@ -1050,7 +1022,7 @@ impl InterfaceInner {
 
     #[cfg(any(feature = "medium-ethernet", feature = "medium-ieee802154"))]
     #[allow(unused)] // unused depending on which sockets are enabled
-    pub(crate) fn hardware_addr(&self) -> Option<HardwareAddress> {
+    pub(crate) fn hardware_addr(&self) -> HardwareAddress {
         self.hardware_addr
     }
 
@@ -1169,19 +1141,31 @@ impl InterfaceInner {
             #[cfg(feature = "proto-ipv4-fragmentation")]
             ipv4_id: 1,
 
+            #[cfg(all(
+                feature = "medium-ip",
+                not(feature = "medium-ethernet"),
+                not(feature = "medium-ieee802154")
+            ))]
+            hardware_addr: crate::wire::HardwareAddress::Ip,
+
             #[cfg(feature = "medium-ethernet")]
-            hardware_addr: Some(crate::wire::HardwareAddress::Ethernet(
-                crate::wire::EthernetAddress([0x02, 0x02, 0x02, 0x02, 0x02, 0x02]),
-            )),
-            #[cfg(all(not(feature = "medium-ethernet"), feature = "medium-ieee802154"))]
-            hardware_addr: Some(crate::wire::HardwareAddress::Ieee802154(
+            hardware_addr: crate::wire::HardwareAddress::Ethernet(crate::wire::EthernetAddress([
+                0x02, 0x02, 0x02, 0x02, 0x02, 0x02,
+            ])),
+
+            #[cfg(all(
+                not(feature = "medium-ip"),
+                not(feature = "medium-ethernet"),
+                feature = "medium-ieee802154"
+            ))]
+            hardware_addr: crate::wire::HardwareAddress::Ieee802154(
                 crate::wire::Ieee802154Address::Extended([
                     0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x2, 0x2,
                 ]),
-            )),
+            ),
 
             #[cfg(any(feature = "medium-ethernet", feature = "medium-ieee802154"))]
-            neighbor_cache: None,
+            neighbor_cache: NeighborCache::new(),
 
             #[cfg(feature = "proto-igmp")]
             igmp_report_state: IgmpReportState::Inactive,
@@ -1199,7 +1183,7 @@ impl InterfaceInner {
     #[cfg(any(feature = "medium-ethernet", feature = "medium-ieee802154"))]
     fn check_hardware_addr(addr: &HardwareAddress) {
         if !addr.is_unicast() {
-            panic!("Ethernet address {addr} is not unicast")
+            panic!("Hardware address {addr} is not unicast")
         }
     }
 
@@ -1503,19 +1487,9 @@ impl InterfaceInner {
         match self.route(addr, self.now) {
             Some(_routed_addr) => match self.caps.medium {
                 #[cfg(feature = "medium-ethernet")]
-                Medium::Ethernet => self
-                    .neighbor_cache
-                    .as_ref()
-                    .unwrap()
-                    .lookup(&_routed_addr, self.now)
-                    .found(),
+                Medium::Ethernet => self.neighbor_cache.lookup(&_routed_addr, self.now).found(),
                 #[cfg(feature = "medium-ieee802154")]
-                Medium::Ieee802154 => self
-                    .neighbor_cache
-                    .as_ref()
-                    .unwrap()
-                    .lookup(&_routed_addr, self.now)
-                    .found(),
+                Medium::Ieee802154 => self.neighbor_cache.lookup(&_routed_addr, self.now).found(),
                 #[cfg(feature = "medium-ip")]
                 Medium::Ip => true,
             },
@@ -1584,12 +1558,7 @@ impl InterfaceInner {
             .route(dst_addr, self.now)
             .ok_or(DispatchError::NoRoute)?;
 
-        match self
-            .neighbor_cache
-            .as_mut()
-            .unwrap()
-            .lookup(&dst_addr, self.now)
-        {
+        match self.neighbor_cache.lookup(&dst_addr, self.now) {
             NeighborAnswer::Found(hardware_addr) => return Ok((hardware_addr, tx_token)),
             NeighborAnswer::RateLimited => return Err(DispatchError::NeighborPending),
             _ => (), // XXX
@@ -1602,7 +1571,7 @@ impl InterfaceInner {
                     "address {} not in neighbor cache, sending ARP request",
                     dst_addr
                 );
-                let src_hardware_addr = self.hardware_addr.unwrap().ethernet_or_panic();
+                let src_hardware_addr = self.hardware_addr.ethernet_or_panic();
 
                 let arp_repr = ArpRepr::EthernetIpv4 {
                     operation: ArpOperation::Request,
@@ -1634,7 +1603,7 @@ impl InterfaceInner {
 
                 let solicit = Icmpv6Repr::Ndisc(NdiscRepr::NeighborSolicit {
                     target_addr: dst_addr,
-                    lladdr: Some(self.hardware_addr.unwrap().into()),
+                    lladdr: Some(self.hardware_addr.into()),
                 });
 
                 let packet = IpPacket::Icmpv6((
@@ -1659,15 +1628,13 @@ impl InterfaceInner {
         }
 
         // The request got dispatched, limit the rate on the cache.
-        self.neighbor_cache.as_mut().unwrap().limit_rate(self.now);
+        self.neighbor_cache.limit_rate(self.now);
         Err(DispatchError::NeighborPending)
     }
 
     fn flush_cache(&mut self) {
         #[cfg(any(feature = "medium-ethernet", feature = "medium-ieee802154"))]
-        if let Some(cache) = self.neighbor_cache.as_mut() {
-            cache.flush()
-        }
+        self.neighbor_cache.flush()
     }
 
     fn dispatch_ip<Tx: TxToken>(
@@ -1722,8 +1689,7 @@ impl InterfaceInner {
                     frag,
                 )? {
                     (HardwareAddress::Ethernet(addr), tx_token) => (addr, tx_token),
-                    #[cfg(feature = "medium-ieee802154")]
-                    (HardwareAddress::Ieee802154(_), _) => unreachable!(),
+                    (_, _) => unreachable!(),
                 }
             }
             _ => (EthernetAddress([0; 6]), tx_token),
@@ -1734,7 +1700,7 @@ impl InterfaceInner {
         let emit_ethernet = |repr: &IpRepr, tx_buffer: &mut [u8]| {
             let mut frame = EthernetFrame::new_unchecked(tx_buffer);
 
-            let src_addr = self.hardware_addr.unwrap().ethernet_or_panic();
+            let src_addr = self.hardware_addr.ethernet_or_panic();
             frame.set_src_addr(src_addr);
             frame.set_dst_addr(dst_hardware_addr);
 
diff --git a/src/iface/interface/tests.rs b/src/iface/interface/tests.rs
index cf4c655f..3345dae7 100644
--- a/src/iface/interface/tests.rs
+++ b/src/iface/interface/tests.rs
@@ -39,7 +39,7 @@ fn create_ip<'a>() -> (Interface, SocketSet<'a>, Loopback) {
     // Create a basic device
     let mut device = Loopback::new(Medium::Ip);
 
-    let mut config = Config::new();
+    let config = Config::new(HardwareAddress::Ip);
     let mut iface = Interface::new(config, &mut device);
     iface.update_ip_addrs(|ip_addrs| {
         #[cfg(feature = "proto-ipv4")]
@@ -64,8 +64,7 @@ fn create_ethernet<'a>() -> (Interface, SocketSet<'a>, Loopback) {
     // Create a basic device
     let mut device = Loopback::new(Medium::Ethernet);
 
-    let mut config = Config::new();
-    config.hardware_addr = Some(EthernetAddress::default().into());
+    let config = Config::new(HardwareAddress::Ethernet(EthernetAddress::default()));
     let mut iface = Interface::new(config, &mut device);
     iface.update_ip_addrs(|ip_addrs| {
         #[cfg(feature = "proto-ipv4")]
@@ -90,8 +89,7 @@ fn create_ieee802154<'a>() -> (Interface, SocketSet<'a>, Loopback) {
     // Create a basic device
     let mut device = Loopback::new(Medium::Ieee802154);
 
-    let mut config = Config::new();
-    config.hardware_addr = Some(Ieee802154Address::default().into());
+    let config = Config::new(HardwareAddress::Ieee802154(Ieee802154Address::default()));
     let mut iface = Interface::new(config, &mut device);
     iface.update_ip_addrs(|ip_addrs| {
         #[cfg(feature = "proto-ipv6")]
@@ -133,11 +131,11 @@ impl TxToken for MockTxToken {
 }
 
 #[test]
-#[should_panic(expected = "hardware_addr required option was not set")]
-#[cfg(all(feature = "medium-ethernet"))]
+#[should_panic(expected = "The hardware address does not match the medium of the interface.")]
+#[cfg(all(feature = "medium-ip", feature = "medium-ethernet"))]
 fn test_new_panic() {
     let mut device = Loopback::new(Medium::Ethernet);
-    let config = Config::new();
+    let config = Config::new(HardwareAddress::Ip);
     Interface::new(config, &mut device);
 }
 
@@ -1377,7 +1375,7 @@ fn test_echo_request_sixlowpan_128_bytes() {
     assert_eq!(iface.inner.caps.medium, Medium::Ieee802154);
     let now = iface.inner.now();
 
-    iface.inner.neighbor_cache.as_mut().unwrap().fill(
+    iface.inner.neighbor_cache.fill(
         Ipv6Address([0xfe, 0x80, 0, 0, 0, 0, 0, 0, 0x2, 0, 0, 0, 0, 0, 0, 0]).into(),
         HardwareAddress::Ieee802154(Ieee802154Address::default()),
         now,
@@ -1503,7 +1501,7 @@ fn test_echo_request_sixlowpan_128_bytes() {
         )))
     );
 
-    iface.inner.neighbor_cache.as_mut().unwrap().fill(
+    iface.inner.neighbor_cache.fill(
         IpAddress::Ipv6(Ipv6Address([
             0xfe, 0x80, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x40, 0x42, 0x42, 0x42, 0x42, 0x42, 0xb, 0x1a,
         ])),
diff --git a/src/socket/dhcpv4.rs b/src/socket/dhcpv4.rs
index d796efaa..2609621e 100644
--- a/src/socket/dhcpv4.rs
+++ b/src/socket/dhcpv4.rs
@@ -317,7 +317,7 @@ impl<'a> Socket<'a> {
             }
         };
 
-        let Some(HardwareAddress::Ethernet(ethernet_addr)) = cx.hardware_addr() else {
+        let HardwareAddress::Ethernet(ethernet_addr) = cx.hardware_addr() else {
             panic!("using DHCPv4 socket with a non-ethernet hardware address.");
         };
 
@@ -542,7 +542,7 @@ impl<'a> Socket<'a> {
     {
         // note: Dhcpv4Socket is only usable in ethernet mediums, so the
         // unwrap can never fail.
-        let Some(HardwareAddress::Ethernet(ethernet_addr)) = cx.hardware_addr() else {
+        let HardwareAddress::Ethernet(ethernet_addr) = cx.hardware_addr() else {
             panic!("using DHCPv4 socket with a non-ethernet hardware address.");
         };
 
diff --git a/src/wire/mod.rs b/src/wire/mod.rs
index 6a308a9f..616af949 100644
--- a/src/wire/mod.rs
+++ b/src/wire/mod.rs
@@ -275,20 +275,32 @@ impl fmt::Display for Error {
 pub type Result<T> = core::result::Result<T, Error>;
 
 /// Representation of an hardware address, such as an Ethernet address or an IEEE802.15.4 address.
-#[cfg(any(feature = "medium-ethernet", feature = "medium-ieee802154"))]
+#[cfg(any(
+    feature = "medium-ip",
+    feature = "medium-ethernet",
+    feature = "medium-ieee802154"
+))]
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 #[cfg_attr(feature = "defmt", derive(defmt::Format))]
 pub enum HardwareAddress {
+    #[cfg(feature = "medium-ip")]
+    Ip,
     #[cfg(feature = "medium-ethernet")]
     Ethernet(EthernetAddress),
     #[cfg(feature = "medium-ieee802154")]
     Ieee802154(Ieee802154Address),
 }
 
-#[cfg(any(feature = "medium-ethernet", feature = "medium-ieee802154"))]
+#[cfg(any(
+    feature = "medium-ip",
+    feature = "medium-ethernet",
+    feature = "medium-ieee802154"
+))]
 impl HardwareAddress {
     pub const fn as_bytes(&self) -> &[u8] {
         match self {
+            #[cfg(feature = "medium-ip")]
+            HardwareAddress::Ip => unreachable!(),
             #[cfg(feature = "medium-ethernet")]
             HardwareAddress::Ethernet(addr) => addr.as_bytes(),
             #[cfg(feature = "medium-ieee802154")]
@@ -299,6 +311,8 @@ impl HardwareAddress {
     /// Query wether the address is an unicast address.
     pub fn is_unicast(&self) -> bool {
         match self {
+            #[cfg(feature = "medium-ip")]
+            HardwareAddress::Ip => unreachable!(),
             #[cfg(feature = "medium-ethernet")]
             HardwareAddress::Ethernet(addr) => addr.is_unicast(),
             #[cfg(feature = "medium-ieee802154")]
@@ -309,6 +323,8 @@ impl HardwareAddress {
     /// Query wether the address is a broadcast address.
     pub fn is_broadcast(&self) -> bool {
         match self {
+            #[cfg(feature = "medium-ip")]
+            HardwareAddress::Ip => unreachable!(),
             #[cfg(feature = "medium-ethernet")]
             HardwareAddress::Ethernet(addr) => addr.is_broadcast(),
             #[cfg(feature = "medium-ieee802154")]
@@ -333,12 +349,30 @@ impl HardwareAddress {
             _ => panic!("HardwareAddress is not Ethernet."),
         }
     }
+
+    #[inline]
+    pub(crate) fn medium(&self) -> Medium {
+        match self {
+            #[cfg(feature = "medium-ip")]
+            HardwareAddress::Ip => Medium::Ip,
+            #[cfg(feature = "medium-ethernet")]
+            HardwareAddress::Ethernet(_) => Medium::Ethernet,
+            #[cfg(feature = "medium-ieee802154")]
+            HardwareAddress::Ieee802154(_) => Medium::Ieee802154,
+        }
+    }
 }
 
-#[cfg(any(feature = "medium-ethernet", feature = "medium-ieee802154"))]
+#[cfg(any(
+    feature = "medium-ip",
+    feature = "medium-ethernet",
+    feature = "medium-ieee802154"
+))]
 impl core::fmt::Display for HardwareAddress {
     fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
         match self {
+            #[cfg(feature = "medium-ip")]
+            HardwareAddress::Ip => write!(f, "no hardware addr"),
             #[cfg(feature = "medium-ethernet")]
             HardwareAddress::Ethernet(addr) => write!(f, "{addr}"),
             #[cfg(feature = "medium-ieee802154")]