diff --git a/nzr-api/src/mock/mod.rs b/nzr-api/src/mock/mod.rs
index 25ee926..cbdbc1c 100644
--- a/nzr-api/src/mock/mod.rs
+++ b/nzr-api/src/mock/mod.rs
@@ -10,7 +10,7 @@ use futures::{future, StreamExt};
 use tokio::{sync::RwLock, task::JoinHandle};
 
 use crate::{
-    error::ApiError,
+    error::{ApiError, ErrorType},
     model,
     net::{cidr::CidrV4, mac::MacAddr},
     InstanceQuery, Nazrin, NazrinClient,
@@ -241,27 +241,32 @@ impl Nazrin for MockServer {
         interface: String,
     ) -> Result<(), ApiError> {
         let mut db = self.db.write().await;
-        db.instances
-            .iter()
-            .filter_map(|inst| inst.as_ref())
-            .for_each(|inst| {
-                if inst.lease.subnet == interface {
-                    todo!("what now")
-                }
-            });
-        let Some(subnet) = db
-            .subnets
-            .iter_mut()
-            .find(|net| net.as_ref().filter(|n| n.name == interface).is_some())
-        else {
-            return Err("Subnet doesn't exist".into());
-        };
-        subnet.take();
+        {
+            let Some(subnet) = db
+                .subnets
+                .iter_mut()
+                .find(|net| net.as_ref().filter(|n| n.name == interface).is_some())
+            else {
+                return Err(ErrorType::NotFound.into());
+            };
+            subnet.take();
+        }
+        // Drop all instances that belong to this subnet
+        db.instances.iter_mut().for_each(|inst| {
+            if inst
+                .as_mut()
+                .filter(|inst| inst.lease.subnet != interface)
+                .is_some()
+            {
+                inst.take();
+            }
+        });
         Ok(())
     }
 
     async fn garbage_collect(self, _: tarpc::context::Context) -> Result<(), ApiError> {
-        todo!()
+        // no libvirt to compare against, no instances to GC
+        Ok(())
     }
 
     async fn get_ssh_pubkeys(