feat: add DHCP subnet (CIDR) configuration parameter

Allow -d to optionally accept a CIDR subnet (e.g. -d 10.0.0.0/24)
to fix the DHCP address range. When specified, the DHCP allocator
uses the configured subnet instead of deriving it from peer IPs.

Changes:
- Add dhcp_cidr field to config struct and ConfigLoader trait
- Modify -d CLI arg to accept optional CIDR string value
- Update DHCP logic to use configured CIDR as default subnet
- Add dhcp_cidr to NetworkConfig proto message
- Update launcher to handle dhcp_cidr in gen_config/new_from_config
- Update i18n translations

easytier/src/common/config.rs

@@ -185,6 +185,9 @@ pub trait ConfigLoader: Send + Sync {
     fn get_dhcp(&self) -> bool;
     fn set_dhcp(&self, dhcp: bool);
 
+    fn get_dhcp_cidr(&self) -> Option<cidr::Ipv4Cidr>;
+    fn set_dhcp_cidr(&self, cidr: Option<cidr::Ipv4Cidr>);
+
     fn add_proxy_cidr(
         &self,
         cidr: cidr::Ipv4Cidr,
@@ -535,6 +538,7 @@ struct Config {
     ipv6_public_addr_auto: Option<bool>,
     ipv6_public_addr_prefix: Option<String>,
     dhcp: Option<bool>,
+    dhcp_cidr: Option<String>,
     network_identity: Option<NetworkIdentity>,
     listeners: Option<Vec<url::Url>>,
     mapped_listeners: Option<Vec<url::Url>>,
@@ -768,6 +772,18 @@ impl ConfigLoader for TomlConfigLoader {
         self.config.lock().unwrap().dhcp = Some(dhcp);
     }
 
+    fn get_dhcp_cidr(&self) -> Option<cidr::Ipv4Cidr> {
+        let locked_config = self.config.lock().unwrap();
+        locked_config
+            .dhcp_cidr
+            .as_ref()
+            .and_then(|s| s.parse().ok())
+    }
+
+    fn set_dhcp_cidr(&self, cidr: Option<cidr::Ipv4Cidr>) {
+        self.config.lock().unwrap().dhcp_cidr = cidr.map(|c| c.to_string());
+    }
+
     fn add_proxy_cidr(
         &self,
         cidr: cidr::Ipv4Cidr,

easytier/src/core.rs

@@ -204,7 +204,7 @@ struct NetworkOptions {
         num_args = 0..=1,
         default_missing_value = "true"
     )]
-    dhcp: Option<bool>,
+    dhcp: Option<String>,
 
     #[arg(
         short,
@@ -907,8 +907,19 @@ impl NetworkOptions {
             cfg.set_network_identity(NetworkIdentity::new_credential(network_name));
         }
 
-        if let Some(dhcp) = self.dhcp {
-            cfg.set_dhcp(dhcp);
+        if let Some(ref dhcp) = self.dhcp {
+            if dhcp == "true" || dhcp == "1" {
+                cfg.set_dhcp(true);
+            } else if dhcp == "false" || dhcp == "0" {
+                cfg.set_dhcp(false);
+            } else {
+                // Treat as CIDR, e.g. "10.0.0.0/24"
+                cfg.set_dhcp(true);
+                let cidr: cidr::Ipv4Cidr = dhcp.parse().with_context(|| {
+                    format!("failed to parse dhcp cidr: {}", dhcp)
+                })?;
+                cfg.set_dhcp_cidr(Some(cidr));
+            }
         }
 
         if let Some(ipv4) = &self.ipv4 {

easytier/src/instance/instance.rs

@@ -829,7 +829,11 @@ impl Instance {
         let nic_ctx = self.nic_ctx.clone();
         let _peer_packet_receiver = self.peer_packet_receiver.clone();
         tokio::spawn(async move {
-            let default_ipv4_addr = Ipv4Inet::new(Ipv4Addr::new(10, 126, 126, 0), 24).unwrap();
+            let default_ipv4_addr = if let Some(dhcp_cidr) = global_ctx_c.config.get_dhcp_cidr() {
+                Ipv4Inet::new(dhcp_cidr.first_address(), dhcp_cidr.network_length()).unwrap()
+            } else {
+                Ipv4Inet::new(Ipv4Addr::new(10, 126, 126, 0), 24).unwrap()
+            };
             let mut current_dhcp_ip: Option<Ipv4Inet> = None;
             let mut next_sleep_time = 0;
             let nic_closed_notifier = Arc::new(Notify::new());
@@ -864,7 +868,11 @@ impl Instance {
                     used_ipv4.insert(peer_ipv4_addr.into());
                 }
 
-                let dhcp_inet = used_ipv4.iter().next().unwrap_or(&default_ipv4_addr);
+                let dhcp_inet = if global_ctx_c.config.get_dhcp_cidr().is_some() {
+                    &default_ipv4_addr
+                } else {
+                    used_ipv4.iter().next().unwrap_or(&default_ipv4_addr)
+                };
                 // if old ip is already in this subnet and not conflicted, use it
                 if let Some(ip) = current_dhcp_ip
                     && ip.network() == dhcp_inet.network()

easytier/src/launcher.rs

@@ -637,6 +637,11 @@ impl NetworkConfig {
         );
         cfg.set_hostname(self.hostname.clone());
         cfg.set_dhcp(self.dhcp.unwrap_or_default());
+        if let Some(ref dhcp_cidr) = self.dhcp_cidr {
+            if let Ok(cidr) = dhcp_cidr.parse::<cidr::Ipv4Cidr>() {
+                cfg.set_dhcp_cidr(Some(cidr));
+            }
+        }
         cfg.set_inst_name(self.network_name.clone().unwrap_or_default());
 
         // The web UI does not expose credential inputs directly, but imported/saved
@@ -1019,6 +1024,7 @@ impl NetworkConfig {
         }
 
         result.dhcp = Some(config.get_dhcp());
+        result.dhcp_cidr = config.get_dhcp_cidr().map(|c| c.to_string());
 
         let network_identity = config.get_network_identity();
         result.network_name = Some(network_identity.network_name.clone());

easytier/src/proto/api_manage.proto

@@ -102,6 +102,7 @@ message NetworkConfig {
   optional bool disable_relay_data = 65;
   optional bool enable_udp_broadcast_relay = 66;
   optional uint32 socket_mark = 67;
+  optional string dhcp_cidr = 68;
 }
 
 message PortForwardConfig {