UDP Option Address

The UDP Option Address (UOA) is a kernel module used to obtain the real source IP/port from the packets sent by load balancer. It is designed to transparently transmit source addresses in UDP load balancing scenarios.

The following UDP load balancing scenarios are supported:

• IPv4
• IPv6
• NAT46 & NAT64

How to use

Requirement

The requirements for compiling the kernel module consists of:

• GNU Compiler Collection
• GNU Make tool
• Kernel Headers

For Ubuntu, we could install the requirements as follows:

sudo apt-get install gcc
sudo apt-get install make
sudo apt-get install linux-headers-$(uname -r)

Build & Install

Download the released source code then compile it:

cd src
make

Load the UOA kernel model:

sudo insmod uoa.ko

Obtain the real source IP/port

In backend server, we could call getsockopt() to obtain the real source IP/port.

We have provided examples of backend servers written by several languages. Lookup the examples directory in source code for details.

How does it work

Step 1: Load Balancer inserts the real source IP/port information into the packet

When the packet passed by, the specific load balancer will insert real source IP/port information into the packet by agreed format:

• For IPv4 packet, real source IP/port information will be inserted as a IPv4 Option
• For IPv6 packet, real source IP/port information will be inserted as a IPv6 Destination Extension Header Option

Both IPv4 and IPv6 Option Type are 0x1f which has not been used by RFC.

Both IPv4 and IPv6 Option formats comply with RFC specifications which are as follows:

IPv4 Option: RFC7126

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
|  option-type  | option-length |  option-data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -

option-type      0x1f
option-length    8 (total length of option)
option-data      sport (2 Byte) + sip (4/16 Byte)



IPv6 Destination Extension Header Option: RFC2460

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Next Header  |  Hdr Ext Len  |                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
|                                                               |
.                                                               .
.                            Options                            .
.                                                               .
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
|  Option Type  |  Opt Data Len |  Option Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -

Next Header      17 (UDP)
Hdr Ext Len      2
Option Type      0x1f
Opt Data Len     18 (length of option data)
Option Data      sport (2 Byte) + sip (4/16 Byte)

Step 2: UOA parses the packet to obtain the real source IP/port information and stores in kernel cache

Step 3: Backend server makes a system call to obtion the real source IP/port from kernel cache

When the UOA kernel module is inserted, it registers the getsockopt() system call, which is used to get the specific real source IP/port information stored in kernel cache.

License

UOA is a kernel module based on DPVS to meet the requirements of cloud services.

UOA is GNU General Public License, version 2 (GPLv2) licensed.