Microsoft Peer-to-Peer Networking : PNRP

Understanding PNRP Clouds

p2p — Tue, 12 Jun 2007 12:00:00 GMT

In the next few days, I'd like to post portions of the debugging guide that we've been compiling. First, we need to explain PNRP clouds and cloud states and run through our powerful but cryptic netsh commands. We'll start with clouds.

A PNRP cloud is a group of connected PNRP nodes. By connected, I mean that paths exist between peers such that any node in the cloud can resolve a name published by any other node.

When you start the PNRP service, it joins multiple clouds. Actually, PNRP bootstraps are lazy and will wait for an application to register or resolve a name before spending any bandwidth.

You can list the clouds your machine is participating in with the netsh p2p pnrp cloud show list command. Here’s an example from my computer:

Scope Id Addr State Name

----- ----- ----- ---------------- -----

3 8 1 Active LinkLocal_2001:4898:28:2::/64

1 0 2 Active Global_

PNRP clouds can be classified by the ipv6 scope that they operate on. Your machine will join clouds in the global, link local and site local scopes. The site local scope has been deprecated, so it’s unlikely you’ll encounter it. We won’t talk about it further.

In the listing above, the scope heading refers to the ipv6 scope of the cloud. Global (1), Site Local (2) or Link Local (3) are all valid possibilities.

The Link Local Scope

PNRP will join a link local cloud for every link local address on your machine. Here’s the output of netsh p2p pnrp cloud show list on a machine with two network cards:

netsh p2p pnrp cloud>show list

Scope Id Addr State Name

----- ----- ----- ------- -----

3 8 1 Active LinkLocal_{1FFC205C-6D0D-43A0-B471-59E9FE0CFF}

3 12 1 Active LinkLocal_2001:4898:28:2::/64

1 0 4 Active Global_

Note the naming scheme. PNRP names the link local cloud using the prefix of the Global address assigned to the interface. If you have two interfaces, and they share a Global prefix, PNRP will name the second link local cloud with a GUID.

The Global Scope

PNRP will join the Global_ cloud if you have a global ipv6 address. If you don’t have a global IPv6 address, the Global_ cloud won’t appear. Here’s the output of netsh p2p pnrp cloud show list on a machine without global connectivity

netsh p2p pnrp cloud>show list

Scope Id Addr State Name

----- ----- ----- ---------------- -----

3 8 1 Active LinkLocal_ff00::%8/8

A PNRP node can only join one global cloud at a time. If you’re interested in running a private PNRP cloud, you can set up your own seed node and configure your clients to bootstrap from it. If you do this, your clients won’t be able to resolve names in the global cloud hosted by Microsoft. Be careful!

Cloud States

Active

The node is connected and has neighbors. You can publish and resolve names. Excepting a few very strange situations, an active cloud is a healthy cloud.

Alone

You don’t have any neighbors, so your publications won’t be reachable and you won’t be able to resolve peers in this cloud. It can be perfectly normal for your link local clouds to be alone. There might not be any other PNRP nodes on your link.

Underlying network problems can prevent your clouds from going active. If you’re alone in a cloud, but don’t think you should be, the cloud probably failed to bootstrap correctly. If your Global_ cloud is in the alone state, you’re likely not able to communicate with the seed server. Your firewall might be misconfigured or your packets might be filtered upstream.

If you’re alone in a link local cloud you might have difficulty communicating with computers nearby. PNRP uses the simple service discovery protocol (SSDP) to find neighboring on-link nodes. If SSDP is disabled on your system, or blocked by the firewall, your link local clouds will not bootstrap correctly.

Virtual

We mentioned earlier that PNRP cloud bootstrapping is a lazy operation. A PNRP cloud that has been created, but not used, will be in the virtual state.

As a further optimization, PNRP suspends itself after fifteen minutes of inactivity. If you don’t have a name published and you aren’t resolving any names you can expect to find your clouds in the virtual state.

No Net

If you pull the wire or wander out of your hotspot, your clouds will switch to the no net state.

Synchronizing

Your cloud is in the process of bootstrapping. The bootstrap operation is pretty quick for both link local and global clouds. You have to be sneaky to catch your cloud synchronizing.

Questions about PNRP clouds? Ask us!

Thanks!

Tyler

tylbart at microsoft.com

Teredo and the PNRP Global Cloud

tylbart — Thu, 22 Mar 2007 03:13:00 GMT

Most applications that use the Windows Peer-to-Peer applications require use the global cloud for most scenarios. However I have found that occasionally the global cloud is not present on some machines. Here is some troubleshooting tips you can perform to get the global cloud up and running.

First of all, a brief review on what the global cloud is. It is nothing more than access to public IPv6 addresses. In theory if your windows machine has a Global IPv6 address your p2p applications can communicate with any other windows machine with Global IPv6 connective. Chances are you do not yet have Native IPv6 connectivity and so you are using a transition technology like Teredo. Teredo is available on both Vista and XP.

It tries to send IPv4 UDP packets to a teredo server (by default Teredo.ipv6.microsoft.com). The server in turn will send back a teredo address for the client to use. The address it sends back is a Global IPv6 address with a prefix of 2001:0::/32. When the application sends a packet from the teredo address to another IPv6 address it will be sent to the destination or to a Teredo relay service to route to the correct address.

How do you check to see if you have access to the global cloud? The simplest way is to run “NETSH P2P PNRP CL SH ST *”. This will enumerate what clouds are available. You will probably see a link local cloud that looks something like this: “LinkLocal_2001:4898:28:3::/64” That cloud will let you communicate with those on your same subnet. The global cloud is named “Global_”. If it is not there then we need to find out why.

Take a look at your teredo state. On vista the command is “Netsh int teredo sh st” On XP it is “Netsh interface ipv6 show teredo”. The state value will tell us if it is working or not. The Error value will tell us why it is not working. If the state is probe that means it is still trying to communicate with the teredo server. You need to give it another minute. If it says dormant or qualified that means it is working. If it says offline then we need to examine the error state.

Sometimes it is clear what the error is. If it says the teredo server is unreachable over UDP then you need to check if it is blocked by a firewall. If you are using the windows firewall the port should have been opened for you. Check any 3^rd party firewalls or your edge firewalls to make sure the traffic is not being blocked. By default Teredo uses a random port. You can set which port you want it to use with the “netsh int ter set state clientport=port” command. You may try to do a regular ping to the teredo server. However the error may not be as clear. If it says “Client is in a managed Network” it means teredo has detected that you are in a corperate environment. If that is the case you need to set the Teredo type to Enterprise client “Netsh int ter set state enterpriseclient”.

Another thing to note is on Vista a IPv6 firewall is required for Teredo to operate. If windows detects there is no IPv6 firewall, teredo will not function. If you use the windows firewall, turn it on. If you use a 3^rd party firewall check with the manufacturer to make sure it reports to windows if it is on or not, and that it covers IPv6.

For more information about Teredo, read the overview at http://www.microsoft.com/technet/prodtechnol/winxppro/maintain/teredo.mspx.

-Travis

Setting up a Private PNRP Global Cloud

tylbart — Sun, 18 Mar 2007 04:55:00 GMT

A PNRP cloud is a collection of computers participating in PNRP name lookups and registrations. PNRP uses two clouds – one for link local operations and the other for global communication through the internet.

You can create a private global cloud by setting up a seed server. Private global clouds are sometimes used by large organizations that aren’t ready to open up their networks to the IPv6 internet but need to enable name resolution across multiple subnets.

A seed server is just a well known PNRP node that can be used for bootstrapping. Microsoft maintains a number of seed servers on the public internet behind pnrpv2.ipv6.microsoft.com and pnrpv21.ipv6.microsoft.com. By default, PNRP v2.0 clients use these servers to start participating in the global cloud.

Any computer running pnrp can act as a seed server, it just needs to keep one name published at all times. A PNRP node without a name published will go dormant and stop learning about the cloud as it changes.

The easiest way to keep a name published is to setup a Windows Internet Computer Name (WICN) on a machine running Windows Vista. Instructions to guide you through WICN setup can be found here:

http://www.microsoft.com/technet/network/p2p/wicn.mspx

Client Setup

There are a number of ways that you can configure client systems to use your new seed server.

Vista keeps a list of seed servers in the registry under the key:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\PeerNet\PNRP\IPV6-Global\Global_\SeedServer

You can view and modify this key directly, or you can use NetSH.

netsh p2p pnrp cloud set seed <address|hostname> <cloud>

Alternatively, you can use your corporate DNS server or the Windows hosts file to override pnrpv2.ipv6.microsoft.com and pnrpv21.ipv6.microsoft.com (default seed servers).

Cloud Separation

PNRP is not designed to deal with multiple global clouds, so you have to take special care to make sure your custom cloud doesn’t merge with the global cloud on the public internet. A single computer accidently connected to multiple clouds will start an irreversible merging process. Network edge controls are a good way to prevent this.

Contact Us

If you’re thinking of setting up a custom seed server, we would like to hear from you. The link local pnrp cloud is good enough for most scenarios inside a corporation. If you’re experimenting with PNRP and considering it for development, let us know so that we can supply you with the best possible guidance and link you into the Microsoft peer-to-peer community.

Have fun!

Tyler (tylbart at microsoft.com)

Writing Peer-to-Peer Applications Using .NET, Part 1 (PNRP)

tylbart — Tue, 13 Mar 2007 00:05:00 GMT

The March CTP of the .Net Framework (codenamed “Orcas”) was released earlier this month. In the CTP you will find a new namespace (System.Net.PeerToPeer) which exposes a rich suite of APIs to make writing Peer-To-Peer (P2P) apps easier. More specifically, the namespace includes APIs for the Peer Name Resolution Protocol (PNRP), People Near Me, Serverless Presence and Application Invitation technologies. This rest of this post will focus on PNRP – part 2 of this series will start to dig into the other technologies being added to the System.Net.PeerToPeer namespace.

What is PNRP?

In short, PRNP is a serverless name resolution technology. It allows one to create an identifier (known as a Peer Name), associate that identifier with data (ip addresses, port #, binary blob, etc) and publish it for other peers to be able to resolve. Sounds a bit like publishing and resolving a DNS host name (ie. Microsoft.com) doesn’t it? Conceptually both technologies allow publishing and resolving identifiers, however, there are key differences that make PNRP well suited for P2P applications. Quoting MSDN:

“Another point of contrast between client/server and peer-to-peer networking is the use of the Domain Name System (DNS). Server computers are typically registered in DNS so that client computers can resolve a name to the IP address of the server computer. Client computers are typically not registered in DNS for the following reasons:
- Many client computers have transient connectivity; they connect for unpredictable amounts of time and can be assigned a new IP address for each connection.
- Client computers do not have shared resources and do not respond to requests for resources. Therefore, other computers do not need to resolve the names of client computers. DNS address records for client computers are not necessary.
Peer computers, on the other hand, have resources to share. However, they still have transient connectivity. Peer computers could use DNS dynamic update to register their names, however, very few DNS servers on the Internet support DNS dynamic update. To be successful for peer-to-peer networking, peer computers must not rely on the existing DNS infrastructure. Therefore, there must be a mechanism to resolve peer names to their addresses that does not rely on DNS. For Windows Peer-to-Peer Networking, this mechanism is Peer Name Resolution Protocol (PNRP) and is described in Peer Name Resolution Protocol.”

Code – Create and Publish a Peer Name

Ok, hopefully now it is clear what PNRP is and why it is so valuable for P2P scenarios. The code below shows how to use the new namespace, System.Net.PeerToPeer to create a PeerName and publish it for other peers to resolve.

NOTE: Be sure to add a reference to System.Net.dll in your VS project as the System.Net.PeerToPeer.dll resides in this new assembly.

using System;

using System.Collections.Generic;

using System.Text;

using System.Net.PeerToPeer;

using System.Net;

namespace PnrpSamples

{

// PNRP Registration Sample

class Program

{

static void Main(string[] args)

{

// Creates a secure (not spoofable) PeerName

PeerName peerName = new PeerName("MikesWebServer", PeerNameType.Secured);

PeerNameRegistration pnReg = new PeerNameRegistration();

pnReg.PeerName = peerName;

pnReg.Port = 80;

//OPTIONAL

//The properties set below are optional. You can register a PeerName without setting these properties

pnReg.Comment = "up to 39 unicode char comment";

pnReg.Data = System.Text.Encoding.UTF8.GetBytes("A data blob associated with the name");

* OPTIONAL

*The properties below are also optional, but will not be set (ie. are commented out) for this example

*pnReg.IPEndPointCollection = // a list of all {IPv4/v6 address, port} pairs to associate with the peername

*pnReg.Cloud = //the scope in which the name should be registered (local subnet, internet, etc)

//Starting the registration means the name is published for others to resolve

pnReg.Start();

Console.WriteLine("Registration of Peer Name: {0} complete.", peerName.ToString());

Console.WriteLine();

Console.WriteLine("Press any key to stop the registration and close the program");

Console.ReadKey();

pnReg.Stop();

}

Output:

Registration of Peer Name: af32f166bc99b4aeabb3e21b152a0eed07daa829.MikesWebServer complete.

Press any key to stop the registration and close the program

At this point we have published a PeerName which other PNRP enabled applications can resolveJ. Later in this post, I show how to write an application that resolves the PeerName we just published, but first, I’m sure you are wondering where on earth the “af32f166bc99b4aeabb3e21b152a0eed07daa829” part of the PeerName came from. To understand this, one needs to know a bit about how Peer Names are constructed. Every PeerName is made up of two parts, an authority, followed by a period and then a classifier. The “af32f166bc99b4aeabb3e21b152a0eed07daa829” in the PeerName created by the application above is the authority. Authorities come in two flavors:

40 hex characters for secure (ie. not spoofable) Peer Names
A single character (the number 0) for unsecure Peer Names

Authorities are generated by the P2P infrastructure, will be different for each user, and are composed of a SHA1 hash of the public key associated with the PeerName. The classifier portion of the PeerName is simply a user defined string of Unicode characters. For all the details of how a PeerName is constructed, click here.

Code – Resolve a Peer Name

The following code snippet shows how to synchronously resolve a PeerName (async methods are also available). It is important to note that once a PeerName is published (as above), it remains published until:

The publisher explicitly stops publishing the name (as in the code example above) OR
The PeerNameRegistration object representing the publication goes out of scope OR
The process which published the PeerName ends

This means that you need to leave the above publisher application running while you execute the code below:

using System;

using System.Collections.Generic;

using System.Text;

using System.Net;

using System.Net.PeerToPeer;

namespace PnrpResolver

{

class Program

{

static void Main(string[] args)

{

// create a resolver object to resolve a peername

PeerNameResolver resolver = new PeerNameResolver();

// the peername to resolve must be passed as the first command line argument to the application

PeerName peerName = new PeerName(args[0]);

// resolve the PeerName - this is a network operation and will block until the resolve completes

PeerNameRecordCollection results = resolver.Resolve(peerName);

// Display the data returned by the resolve operation

Console.WriteLine("Results for PeerName: {0}", peerName);

Console.WriteLine();

int count = 1;

foreach (PeerNameRecord record in results)

{

Console.WriteLine("Record #{0} results...", count);

Console.Write("Comment:");

if (record.Comment != null)

{

Console.Write(record.Comment);

}

Console.WriteLine();

Console.Write("Data:");

if (record.Data != null)

{

Console.Write(System.Text.Encoding.ASCII.GetString(record.Data));

}

Console.WriteLine();

Console.WriteLine("Endpoints:");

foreach (IPEndPoint endpoint in record.EndPointCollection){

Console.WriteLine("\t Endpoint:{0}", endpoint);

Console.WriteLine();

}

count++;

}

Console.ReadKey();

}

Output:

Results for PeerName: af32f166bc99b4aeabb3e21b152a0eed07daa829.MikesWebServer

Record #1 results...

Comment: up to 39 unicode char comment

Data: A data blob associated with the name

Endpoints:

Endpoint:fe80::8d02:5afb:549d:4a78%10:80

Endpoint:10.252.40.98:80

Platform Support & Questions/Comments

All the APIs shown above are available in the March “Orcas” .Net Framework CTP. Note: The CTP does not yet support Windows Vista.

The PNRP APIs are supported on Windows Vista (all SKUs except starter edition), Windows Server Longhorn as well as Windows XP (with the PNRP update for XP installed).

If you have any questions about the APIs, I encourage you to post them to the System.Net forum. For suggestions with respect to this or any of the System.Net APIs, please email nclasks at microsoft.com

Cheers,

Mike Flasko