diff --git a/Cargo.lock b/Cargo.lock
index 6482292..b6d216f 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,6 +2,15 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "aho-corasick"
+version = "1.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8e60d3430d3a69478ad0993f19238d2df97c507009a52b3c10addcd7f6bcb916"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "cfg-if"
 version = "1.0.0"
@@ -25,11 +34,19 @@ version = "0.2.155"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "97b3888a4aecf77e811145cadf6eef5901f4782c53886191b2f693f24761847c"
 
+[[package]]
+name = "memchr"
+version = "2.7.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "78ca9ab1a0babb1e7d5695e3530886289c18cf2f87ec19a575a0abdce112e3a3"
+
 [[package]]
 name = "minimon"
 version = "0.1.0"
 dependencies = [
  "ping",
+ "regex",
+ "thiserror",
 ]
 
 [[package]]
@@ -97,6 +114,35 @@ dependencies = [
  "getrandom",
 ]
 
+[[package]]
+name = "regex"
+version = "1.10.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b91213439dad192326a0d7c6ee3955910425f441d7038e0d6933b0aec5c4517f"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-automata",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-automata"
+version = "0.4.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "38caf58cc5ef2fed281f89292ef23f6365465ed9a41b7a7754eb4e26496c92df"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.8.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a66a03ae7c801facd77a29370b4faec201768915ac14a721ba36f20bc9c209b"
+
 [[package]]
 name = "socket2"
 version = "0.4.10"
diff --git a/Cargo.toml b/Cargo.toml
index 117bbe6..b2a058d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,3 +5,5 @@ edition = "2021"
 
 [dependencies]
 ping = "0.5.2"
+regex = "1.10.5"
+thiserror = "1.0.61"
diff --git a/src/hostname.rs b/src/hostname.rs
new file mode 100644
index 0000000..a04fe6e
--- /dev/null
+++ b/src/hostname.rs
@@ -0,0 +1,69 @@
+use ::thiserror::Error;
+use regex::Regex;
+
+const VALID_IP_ADDRESS_PATTERN: &str = r"^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$";
+const VALID_HOSTNAME_PATTERN: &str = r"^(([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]*[a-zA-Z0-9])\.)*([A-Za-z0-9]|[A-Za-z0-9][A-Za-z0-9\-]*[A-Za-z0-9])$";
+
+#[derive(Clone, Debug, Error)]
+#[error("The hostname \"{0}\" is invalid")]
+pub struct InvalidHostnameError(String);
+
+pub struct Hostname {
+    hostname: String,
+}
+
+impl Hostname {
+    pub fn new(hostname: &str) -> Result<Hostname, InvalidHostnameError> {
+        if Self::is_valid_ip(&hostname) || Self::is_valid_hostname(&hostname) {
+            Ok(Hostname {
+                hostname: hostname.to_string(),
+            })
+        } else {
+            Err(InvalidHostnameError(hostname.to_string()))
+        }
+    }
+
+    fn is_valid_ip(ip: &str) -> bool {
+        let re = Regex::new(VALID_IP_ADDRESS_PATTERN).unwrap();
+        re.is_match(ip)
+    }
+    fn is_valid_hostname(hostname: &str) -> bool {
+        let re = Regex::new(VALID_HOSTNAME_PATTERN).unwrap();
+        re.is_match(hostname)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn valid_ip_adresses() {
+        assert!(Hostname::new("192.168.0.1").is_ok());
+        assert!(Hostname::new("255.127.63.31").is_ok());
+        assert!(Hostname::new("1.0.0.1").is_ok());
+        assert!(Hostname::new("10.1.10.47").is_ok());
+    }
+
+    #[test]
+    fn invalid_ip_adresses() {
+        assert!(Hostname::new("::1").is_err()); // We don't support IPv6 yet
+    }
+
+    #[test]
+    fn valid_hostnames() {
+        assert!(Hostname::new("mononobe.fai.st").is_ok());
+        assert!(Hostname::new("twink-pad").is_ok());
+        assert!(Hostname::new("is-42-the-response").is_ok());
+        assert!(Hostname::new("GoB.NaSa-42.eu").is_ok());
+        assert!(Hostname::new("256.127.63.31").is_ok());
+    }
+
+    #[test]
+    fn invalid_hostnames() {
+        assert!(Hostname::new("no..double.dots").is_err());
+        assert!(Hostname::new("#illegal-character").is_err()); // We don't support IPv6 yet
+        assert!(Hostname::new("").is_err());
+        assert!(Hostname::new("not-end-with-hyphen-").is_err());
+    }
+}
diff --git a/src/machine.rs b/src/machine.rs
index 305a59e..3b6284a 100644
--- a/src/machine.rs
+++ b/src/machine.rs
@@ -1,38 +1,30 @@
-use std::{collections::HashMap, net::IpAddr};
+use crate::hostname::Hostname;
+use std::collections::HashMap;
 
 pub struct Machine {
     name: String,
-    address: IpAddr,
+    hostname: Hostname,
 }
 
-enum Status {
+pub enum Status {
     Unreachable,
     Forbidden,
     Success(HashMap<String, String>),
 }
 
 impl Machine {
-    fn new(name: &str, address: IpAddr) -> Machine {
+    pub fn new(name: &str, hostname: Hostname) -> Machine {
         Machine {
             name: String::from(name),
-            address,
+            hostname,
         }
     }
 }
 
-trait Monitor {
+pub trait Monitor {
     fn monitor(machine: &Machine) -> Status;
 }
 
-#[derive(Debug)]
-struct PingMonitor {}
-
-impl Monitor for PingMonitor {
-    fn monitor(machine: &Machine) -> Status {
-        todo!()
-    }
-}
-
 #[derive(Debug)]
 struct SshMonitor {}
 
diff --git a/src/main.rs b/src/main.rs
index 66c2c90..56152c9 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,5 +1,6 @@
+mod hostname;
 mod machine;
-
+mod ping_monitor;
 use machine::Machine;
 
 fn main() {
diff --git a/src/ping_monitor.rs b/src/ping_monitor.rs
new file mode 100644
index 0000000..cbc7a25
--- /dev/null
+++ b/src/ping_monitor.rs
@@ -0,0 +1,18 @@
+use crate::machine::{Machine, Monitor, Status};
+
+#[derive(Debug)]
+struct PingMonitor {}
+
+impl Monitor for PingMonitor {
+    fn monitor(machine: &Machine) -> Status {
+        todo!()
+    }
+}
+
+#[cfg(test)]
+mod test {
+    #[test]
+    fn monitor_works() {
+        assert!(true)
+    }
+}