net.i2p.router.transport.udp
Class IntroductionManager

java.lang.Object
  extended by net.i2p.router.transport.udp.IntroductionManager

 class IntroductionManager
extends Object

Keep track of inbound and outbound introductions. IPv6 info: Alice-Bob communication may be via IPv4 or IPv6. Bob-Charlie communication must be via established IPv4 session as that's the only way that Bob knows Charlie's IPv4 address to give it to Alice. Alice-Charlie communication is via IPv4. If Alice-Bob is over IPv6, Alice must include her IPv4 address in the RelayRequest message. From udp.html on the website:

Indirect session establishment by means of a third party introduction is necessary for efficient NAT traversal. Charlie, a router behind a NAT or firewall which does not allow unsolicited inbound UDP packets, first contacts a few peers, choosing some to serve as introducers. Each of these peers (Bob, Bill, Betty, etc) provide Charlie with an introduction tag - a 4 byte random number - which he then makes available to the public as methods of contacting him. Alice, a router who has Charlie's published contact methods, first sends a RelayRequest packet to one or more of the introducers, asking each to introduce her to Charlie (offering the introduction tag to identify Charlie). Bob then forwards a RelayIntro packet to Charlie including Alice's public IP and port number, then sends Alice back a RelayResponse packet containing Charlie's public IP and port number. When Charlie receives the RelayIntro packet, he sends off a small random packet to Alice's IP and port (poking a hole in his NAT/firewall), and when Alice receives Bob's RelayResponse packet, she begins a new full direction session establishment with the specified IP and port.

Alice first connects to introducer Bob, who relays the request to Charlie.

        Alice                         Bob                  Charlie
    RelayRequest ---------------------->
         <-------------- RelayResponse    RelayIntro ----------->
         <-------------------------------------------- HolePunch (data ignored)
    SessionRequest -------------------------------------------->
         <-------------------------------------------- SessionCreated
    SessionConfirmed ------------------------------------------>
         <-------------------------------------------- DeliveryStatusMessage
         <-------------------------------------------- DatabaseStoreMessage
    DatabaseStoreMessage -------------------------------------->
    Data <--------------------------------------------------> Data

After the hole punch, the session is established between Alice and Charlie as in a direct establishment.


Field Summary
static int MAX_OUTBOUND
          This is enforced in EstablishmentManager
 
Constructor Summary
IntroductionManager(RouterContext ctx, UDPTransport transport)
           
 
Method Summary
 void add(PeerState peer)
           
(package private)  int introducedCount()
           
(package private)  int introducerCount()
          Not as elaborate as pickInbound() above.
 int pickInbound(Properties ssuOptions, int howMany)
          Grab a bunch of peers who are willing to be introducers for us that are locally known (duh) and have published their own SSU address (duh^2).
 void pingIntroducers()
          Was part of pickInbound(), moved out so we can call it more often
(package private)  void receiveRelayIntro(RemoteHostId bob, UDPPacketReader reader)
          We are Charlie and we got this from Bob.
(package private)  void receiveRelayRequest(RemoteHostId alice, UDPPacketReader reader)
          We are Bob and we got this from Alice.
 void remove(PeerState peer)
           
 void reset()
           
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

MAX_OUTBOUND

public static final int MAX_OUTBOUND
This is enforced in EstablishmentManager

Since:
0.8.11
See Also:
Constant Field Values
Constructor Detail

IntroductionManager

public IntroductionManager(RouterContext ctx,
                           UDPTransport transport)
Method Detail

reset

public void reset()

add

public void add(PeerState peer)

remove

public void remove(PeerState peer)

pickInbound

public int pickInbound(Properties ssuOptions,
                       int howMany)
Grab a bunch of peers who are willing to be introducers for us that are locally known (duh) and have published their own SSU address (duh^2). The picked peers have their info tacked on to the ssuOptions parameter for use in the SSU RouterAddress. Try to use "good" peers (i.e. reachable, active) Also, ping all idle peers that were introducers in the last 2 hours, to keep the connection up, since the netDb can have quite stale information, and we want to keep our introducers valid.


pingIntroducers

public void pingIntroducers()
Was part of pickInbound(), moved out so we can call it more often

Since:
0.8.11

introducerCount

int introducerCount()
Not as elaborate as pickInbound() above. Just a quick check to see how many volunteers we know, which the Transport uses to see if we need more.

Returns:
number of peers that have volunteered to introduce us

introducedCount

int introducedCount()
Returns:
number of peers we have volunteered to introduce
Since:
0.9.3

receiveRelayIntro

void receiveRelayIntro(RemoteHostId bob,
                       UDPPacketReader reader)
We are Charlie and we got this from Bob. Send a HolePunch to Alice, who will soon be sending us a RelayRequest. We should already have a session with Bob, but probably not with Alice. If we don't have a session with Bob, we removed the relay tag from our _outbound table, so this won't work. We do some throttling here.


receiveRelayRequest

void receiveRelayRequest(RemoteHostId alice,
                         UDPPacketReader reader)
We are Bob and we got this from Alice. Send a RelayIntro to Charlie and a RelayResponse to Alice. We should already have a session with Charlie, but not necessarily with Alice.