DhtPacket Human documentation

[NamsooCho]

Description of DHT packets

1. Overview

PingRequest and NodesRequest provide method to interact with Tox Networks.

• Purpose of packet

  • PingRequest : check if the node is alive
  • NodesRequest : get nodes closest to me and my friends.
  • NatPingRequest : check if my friend is behind NAT, then punch hole

• Data types used

  • Kbucket : contains nodes closest to me
  • Bucket : contains nodes closest to my friend, nodes to bootstrap

2. PingRequest

• When DHT node receives PingRequest, it responds with PingResponse and sends PingRequest.

• When DHT node receives NodesRequest, it responds with NodesResponse and sends PingRequest.

• Before DHT node sends PingRequest, it checks if the node is addable to close list

  • addable : send PingRequest
  • not addable: don't send PingRequest

3. PingResponse

• When DHT node receives PingResponse, it checks if the node is addable to close list
  • addable : add node to close list and friend's close list
  • not addable : don't add node to close list

4. NodesRequest

There are two timers interval

• 60 seconds interval : to ping nodes in close list and friend's close list
• 20 seconds interval : to get nodes close to me and my friends
  • 20 seconds interval timer expires only 5 times after start-up.

There are two case sending NodesRequest

• on two timers expire
• bootstrapping

BootStrapping is checking nodes whether it is alive or not.

The nodes to bootstrap are nodes in NodesResponse and if

• the node is addable to close list of my Public Key or
• the node is addable to close list of my friend's Public Key

When DHT node receives NodesRequest, it responds with NodesResponse.

NodesResponse contains maximum 4 nodes in close list and friend's close list.

Maximum 4 nodes are closest to requested Public Key.

5. NodesResponse

When DHT node receives NodesResponse, it unpack nodes in packet's payload.

Unpacked nodes are added to

• if addable to close list, add
• if addable to close list of my friend, add
• if addable to bootstrap list, add
• if addable to bootstrap list of my friend, add

6. Replacing order of Kbucket and Bucket

Nodes in close list have two status

• Good : node is alive and 'alive' is meaning that last responding time is within 182 seconds.
• Bad : node is not alive, which means last responding time exceeds 182 seconds.

The old node in close list is replaced by new node order by

• Bad and farthest
• Good and farther than new node
• if there is no bad or no (good and father than new node), then new node is not addable

7. NatPingRequest

If a friend is not connected with me and friend is online, at every 3 seconds

• send NatPingRequest to all entry of close_nodes of the friend

Close nodes of a friend have SocketAddrs, if

• more than half of ip addresses are same and
• last time of receiving NatPingResponse is within 6 seconds and
• do_hole_punching variable == 1

are true then starts hole punching.

When DHT node receives NatPingRequest, it checks if Receiver PK is same with my PK

• if same PK, find Sender's PK in my friend's list
  • if found, responds with NatPingResponse
  • if not found, do nothing
• if not same, search DHT node's close list to find same PK
  • if found, send NatPingRequest to the node
  • if not found, do nothing

8. NatPingResponse

When DHT node receives NatPingResponse, it checks if Receiver PK is same with my PK

• if same PK, find Sender's PK in my friend's list
  • if found, check if ping_id is same with ping_id saved
    • if same, set do_hole_punching variable to 1
    • if not same, do nothing
  • if not found, do nothing
• if not same, search DHT node's close list to find same PK
  • if found, send NatPingResponse to the node
  • if not found, do nothing

[kurnevsky]

When we send PingRequest:

• node made PingRequest to us
• node made NodesRequest to us

When we send NodesRequest:

• we got node from NodesResponse
• we loaded node from saved state
• it's node from initial bootstrap list

When we just add to kbucket:

• we got PingResponse from node
• we got NodesResponse from node

[NamsooCho]

The bootstrap_nodes has only 8 nodes from NodesResponses.
These nodes are close to PK of friend.
If the node gotten by NodesResponse is far from PK of friend, then the node is discarded.

[kpp]

The bootstrap_nodes has only 8 nodes from NodesResponses.

https://github.com/tox-rs/tox/blob/master/src/toxcore/dht/packet/nodes_response.rs#L133

[NamsooCho]

Yes, one NodesResponse has maximum 4 nodes.
DHT node receives many NodesReponse packet,
a friend can have maximum 8nodes from many NodesResponse packets