diff --git a/lib/ipaddr.rb b/lib/ipaddr.rb
index cd40d35..96c8918 100644
--- a/lib/ipaddr.rb
+++ b/lib/ipaddr.rb
@@ -216,6 +216,12 @@ def to_string
     return _to_string(@addr)
   end
 
+  # Returns a string containing the IP address representation in
+  # cidr notation
+  def cidr
+    format("%s/%s", to_s, prefix)
+  end
+
   # Returns a network byte ordered string form of the IP address.
   def hton
     case @family
diff --git a/test/test_ipaddr.rb b/test/test_ipaddr.rb
index 42b5214..68c1096 100644
--- a/test/test_ipaddr.rb
+++ b/test/test_ipaddr.rb
@@ -20,18 +20,21 @@ def test_s_new
     a = IPAddr.new
     assert_equal("::", a.to_s)
     assert_equal("0000:0000:0000:0000:0000:0000:0000:0000", a.to_string)
+    assert_equal("::/128", a.cidr)
     assert_equal(Socket::AF_INET6, a.family)
     assert_equal(128, a.prefix)
 
     a = IPAddr.new("0123:4567:89ab:cdef:0ABC:DEF0:1234:5678")
     assert_equal("123:4567:89ab:cdef:abc:def0:1234:5678", a.to_s)
     assert_equal("0123:4567:89ab:cdef:0abc:def0:1234:5678", a.to_string)
+    assert_equal("123:4567:89ab:cdef:abc:def0:1234:5678/128", a.cidr)
     assert_equal(Socket::AF_INET6, a.family)
     assert_equal(128, a.prefix)
 
     a = IPAddr.new("3ffe:505:2::/48")
     assert_equal("3ffe:505:2::", a.to_s)
     assert_equal("3ffe:0505:0002:0000:0000:0000:0000:0000", a.to_string)
+    assert_equal("3ffe:505:2::/48", a.cidr)
     assert_equal(Socket::AF_INET6, a.family)
     assert_equal(false, a.ipv4?)
     assert_equal(true, a.ipv6?)
@@ -41,18 +44,21 @@ def test_s_new
     a = IPAddr.new("3ffe:505:2::/ffff:ffff:ffff::")
     assert_equal("3ffe:505:2::", a.to_s)
     assert_equal("3ffe:0505:0002:0000:0000:0000:0000:0000", a.to_string)
+    assert_equal("3ffe:505:2::/48", a.cidr)
     assert_equal(Socket::AF_INET6, a.family)
     assert_equal(48, a.prefix)
 
     a = IPAddr.new("0.0.0.0")
     assert_equal("0.0.0.0", a.to_s)
     assert_equal("0.0.0.0", a.to_string)
+    assert_equal("0.0.0.0/32", a.cidr)
     assert_equal(Socket::AF_INET, a.family)
     assert_equal(32, a.prefix)
 
     a = IPAddr.new("192.168.1.2")
     assert_equal("192.168.1.2", a.to_s)
     assert_equal("192.168.1.2", a.to_string)
+    assert_equal("192.168.1.2/32", a.cidr)
     assert_equal(Socket::AF_INET, a.family)
     assert_equal(true, a.ipv4?)
     assert_equal(false, a.ipv6?)
@@ -61,6 +67,7 @@ def test_s_new
     a = IPAddr.new("192.168.1.2/26")
     assert_equal("192.168.1.0", a.to_s)
     assert_equal("192.168.1.0", a.to_string)
+    assert_equal("192.168.1.0/26", a.cidr)
     assert_equal(Socket::AF_INET, a.family)
     assert_equal("#<IPAddr: IPv4:192.168.1.0/255.255.255.192>", a.inspect)
     assert_equal(26, a.prefix)
@@ -68,6 +75,7 @@ def test_s_new
     a = IPAddr.new("192.168.1.2/255.255.255.0")
     assert_equal("192.168.1.0", a.to_s)
     assert_equal("192.168.1.0", a.to_string)
+    assert_equal("192.168.1.0/24", a.cidr)
     assert_equal(Socket::AF_INET, a.family)
     assert_equal(24, a.prefix)