diff --git a/Makefile.am b/Makefile.am
index 4511207..db2279f 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -14,6 +14,8 @@ glorytun_SOURCES = \
     src/option.h \
     src/tun.c \
     src/tun.h \
+    src/iface.c \
+    src/iface.h \
     src/db.c \
     src/db.h
 
diff --git a/src/iface.c b/src/iface.c
new file mode 100644
index 0000000..b047889
--- /dev/null
+++ b/src/iface.c
@@ -0,0 +1,29 @@
+#include "common.h"
+
+#include "str.h"
+
+#include <sys/ioctl.h>
+#include <net/if.h>
+
+int
+iface_set_mtu(char *dev_name, int mtu)
+{
+    struct ifreq ifr = {
+        .ifr_mtu = mtu,
+    };
+
+    str_cpy(ifr.ifr_name, dev_name, IFNAMSIZ - 1);
+
+    int fd = socket(AF_INET, SOCK_DGRAM, 0);
+
+    if (fd == -1)
+        return -1;
+
+    int ret = ioctl(fd, SIOCSIFMTU, &ifr);
+
+    int err = errno;
+    close(fd);
+    errno = err;
+
+    return ret;
+}
diff --git a/src/iface.h b/src/iface.h
new file mode 100644
index 0000000..01baf8d
--- /dev/null
+++ b/src/iface.h
@@ -0,0 +1,3 @@
+#pragma once
+
+int iface_set_mtu (char *, int);
diff --git a/src/main.c b/src/main.c
index 45c1e03..4da1fe7 100644
--- a/src/main.c
+++ b/src/main.c
@@ -5,6 +5,7 @@
 #include "option.h"
 #include "str.h"
 #include "tun.h"
+#include "iface.h"
 
 #include <fcntl.h>
 #include <inttypes.h>
@@ -263,7 +264,7 @@ gt_setup_mtu(struct mud *mud, char *tun_name)
 
     gt_log("setup MTU to %i on interface %s\n", mtu, tun_name);
 
-    if (tun_set_mtu(tun_name, mtu) == -1)
+    if (iface_set_mtu(tun_name, mtu) == -1)
         perror("tun_set_mtu");
 }
 
diff --git a/src/tun.c b/src/tun.c
index cd88ab1..f2b8532 100644
--- a/src/tun.c
+++ b/src/tun.c
@@ -239,29 +239,6 @@ tun_write(int fd, const void *data, size_t size)
 #endif
 }
 
-int
-tun_set_mtu(char *dev_name, int mtu)
-{
-    struct ifreq ifr = {
-        .ifr_mtu = mtu,
-    };
-
-    str_cpy(ifr.ifr_name, dev_name, IFNAMSIZ - 1);
-
-    int fd = socket(AF_INET, SOCK_DGRAM, 0);
-
-    if (fd == -1)
-        return -1;
-
-    int ret = ioctl(fd, SIOCSIFMTU, &ifr);
-
-    int err = errno;
-    close(fd);
-    errno = err;
-
-    return ret;
-}
-
 int
 tun_set_persist(int fd, int on)
 {
diff --git a/src/tun.h b/src/tun.h
index df99d74..86bb252 100644
--- a/src/tun.h
+++ b/src/tun.h
@@ -3,5 +3,4 @@
 int tun_create      (char *, char **);
 int tun_read        (int, void *, size_t);
 int tun_write       (int, const void *, size_t);
-int tun_set_mtu     (char *, int);
 int tun_set_persist (int, int);