diff --git a/mdb/models.py b/mdb/models.py
index ea9204f..d4f429c 100644
--- a/mdb/models.py
+++ b/mdb/models.py
@@ -2,6 +2,8 @@ from django.db import models
 from django.db.models.signals import post_save, pre_save, pre_delete
 from django.dispatch import receiver
 
+from validators import validate_hostname
+
 import ipaddr
 import datetime
 
@@ -411,7 +413,7 @@ class Host(models.Model):
 	brand = models.CharField(max_length=1024)
 	model = models.CharField(max_length=1024)
 	owner = models.CharField(max_length=1024)
-	hostname = models.CharField(max_length=64)
+	hostname = models.CharField(max_length=64, validators=[validate_hostname])
 	serial_number = models.CharField(max_length=256)
 	description = models.CharField(max_length=1024)
 	created_date = models.DateTimeField(auto_now_add=True)
@@ -462,7 +464,7 @@ class Interface(models.Model):
 	pxe_filename = models.CharField(max_length=64, blank=True)
 	dhcp_client = models.BooleanField()
 	host = models.ForeignKey(Host)
-	ip4address = models.ForeignKey(Ip4Address, blank=True, null=True)
+	ip4address = models.ForeignKey(Ip4Address, blank=True, null=True, unique=True)
 	created_date = models.DateTimeField(auto_now_add=True)
 	domain = models.ForeignKey(Domain)
 	
diff --git a/mdb/validators.py b/mdb/validators.py
new file mode 100644
index 0000000..91861a5
--- /dev/null
+++ b/mdb/validators.py
@@ -0,0 +1,5 @@
+from django.core.validators import RegexValidator
+import re
+# http://en.wikipedia.org/wiki/Hostname#Restrictions_on_valid_host_names
+hostname_re = re.compile(r'^(?!-)[-a-z0-9]+(?<!-)$', re.IGNORECASE)
+validate_hostname = RegexValidator(hostname_re, u'Enter a valid hostname', 'invalid')