class IntroductionManager extends Object
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.
Modifier and Type | Field and Description |
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static int |
MAX_OUTBOUND
This is enforced in EstablishmentManager
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Constructor and Description |
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IntroductionManager(RouterContext ctx,
UDPTransport transport) |
Modifier and Type | Method and Description |
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void |
add(PeerState peer) |
(package private) int |
introducedCount()
Combined IPv4 and IPv6
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(package private) int |
introducerCount(boolean ipv6)
Not as elaborate as pickInbound() above.
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boolean |
isInboundTagValid(long tag)
Is this inbound tag currently valid,
i.e.
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int |
pickInbound(RouterAddress current,
boolean ipv6,
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).
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void |
pingIntroducers()
Was part of pickInbound(), moved out so we can call it more often
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(package private) void |
receiveRelayIntro(RemoteHostId bob,
UDPPacketReader reader)
We are Charlie and we got this from Bob.
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(package private) void |
receiveRelayRequest(RemoteHostId alice,
UDPPacketReader reader)
We are Bob and we got this from Alice.
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void |
remove(PeerState peer) |
void |
reset() |
public static final int MAX_OUTBOUND
public IntroductionManager(RouterContext ctx, UDPTransport transport)
public void reset()
public void add(PeerState peer)
public void remove(PeerState peer)
public boolean isInboundTagValid(long tag)
public int pickInbound(RouterAddress current, boolean ipv6, Properties ssuOptions, int howMany)
current
- current router address, may be nullipv6
- what type is the current address we need introducers for?ssuOptions
- out parameter, options are addedpublic void pingIntroducers()
int introducerCount(boolean ipv6)
ipv6
- what type of address are they introducing us forint introducedCount()
void receiveRelayIntro(RemoteHostId bob, UDPPacketReader reader)
void receiveRelayRequest(RemoteHostId alice, UDPPacketReader reader)