CrossRoad Billboard: How to Support IP v6 in .NET/C#

In the past, I thought I needn’t do anything to support IP v6. Well, at that moment I knew little of IP v6.

Last month I finally had a chance to study IP v6 with Windows Vista and Server 2008. From then on, I know that as a new protocol, it is not a small jump from the IP v4 boat to the IP v6 one.

Last weekend I started to implement the notification panel of browser. After finding a way to list all IP addresses that I am interested, I knew it is time to add IP v6 support as there is an IP v6 address listed. But how? Interesting that this time I was driven by exceptions and Google.

Do you know the following exception messages?

• “The system detected an invalid pointer address in attempting to use a pointer argument in a call”
• “An address incompatible with the requested protocol was used”

Well, Google reveals that they are the hints that you need to search for all Socket/UdpClient` objects used and let them aware of IP v6 existence.

My changes are,

1. Specify AddressFamily parameter when creating a Socket object. From then on, this Socket object will only be used for IP v4 or v6.
2. Every time an IPAddress object is used, check its AddressFamily so that a proper Socket object can be used.

The toughest problem is how to monitor incoming packets for “All Unassigned”. Ha, you must wonder why monitoring IPAddress.Any is not enough. OK, here is the answer.

IPAddress.Any is for IP v4 only. IPAddress.IPv6Any must be used besides to monitor IP v6 packets. So finally I have to use two Socket objects in this panel. One is used for IP v4, and the other for IP v6.

It is perfect that I have this notification panel completed and in the meantime IP v6 support is accomplished. .NET platform really makes the progress quite smooth.