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diff --git a/content/docs/network_protocols.md b/content/docs/network_protocols.md new file mode 100644 index 0000000..d162945 --- /dev/null +++ b/content/docs/network_protocols.md @@ -0,0 +1,135 @@ +--- +title: "Packet network protocols" +author: "Dimitri Staessens" +description: "what" +date: 2019-09-05 +#type: page +draft: false +--- + +Packet switched networks move data between two applications using +_protocols_, which specify where to move the data and how to do it. +The Internet famously uses the Internet Protocol, IP (versions 4 and +6, which are mutually incompatible, so in essence, there is not a +single Internet, there are two!) as the network protocol that +specifies how to move packets from point _A_ to point _B_. On top, it +has the Transport Control Protocol (TCP) that takes care of things +when IP packets get lost. TCP also does some other neat things, like +making sure that a client does not send faster than a server can +process, usually called _flow control_; and making sure that the +network doesn't get overwhelmed by its users, usually called +_congestion control_. + +The IPv4 protocol is specified in +[RFC791](https://tools.ietf.org/html/rfc791), and its _header_ is +shown here: + +``` + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + |Version| IHL |Type of Service| Total Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Identification |Flags| Fragment Offset | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Time to Live | Protocol | Header Checksum | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Source Address | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Destination Address | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Options | Padding | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +``` + +The IPv6 protocol is specified in +[RFC2460](https://tools.ietf.org/html/rfc2460), and its header format +is: + +``` + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + |Version| Traffic Class | Flow Label | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Payload Length | Next Header | Hop Limit | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + + + + | | + + Source Address + + | | + + + + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + + + + | | + + Destination Address + + | | + + + + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +``` + +For a detailed description of what all the fields in this protocol +mean, we gladly refer you to the RFCs or the wikipedia pages ( +[IPv4](https://en.wikipedia.org/wiki/IPv4) and +[IPv6](https://en.wikipedia.org/wiki/IPv6)). The most interesting +fact about the jump from IPv4 to IPv6 is that the protocol got +noticeably simpler. + +As Ouroboros tries to preserve privacy as much as possible, it has an +*absolutely minimal network protocol* (it's also configurable, this is +the 64 bit address, 16 bit EID version): + +``` + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + + Destination Address + + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Time-to-Live | QoS | ECN | EID | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | EID | + +-+-+-+-+-+-+-+-+ +``` + +The fields are: + +* Destination address: This specifies the address to forward the + packet to. The width of this field is configurable based on various + preferences and the size of the envisioned network. The Ouroboros + default is 64 bits. Note that there is _no source address_, this is + agreed upon during _flow allocation_. + +* Time-to-Live: Similar to IPv4 and IPv6 (where this field is called + Hop Limit), this ensures that packets don't get forwarded forever in + the network, for instance due to (transient) loops in the forwarding + path. + +* QoS: Ouroboros supports Quality of Service via a number of methods + (out of scope for this page), and this field is used to prioritize + scheduling of the packets when forwarding. For instance, if the + network gets congested and queues start filling up, higher priority + packets (e.g. a voice call) get scheduled more often than lower + priority packets (e.g. a file download). + +* ECN: This field specifies Explicit Congestion Notification (ECN), + with similar intent as the ECN bits in the DSCP field in IPv4 / ToS + field in IPv6. It has 8-bit width as a default, and gets set higher + as packets are deeper and deeper in a forwarding queue. Ouroboros + enforces Forward ECN (FECN). + +* EID: The Endpoint Identifier (EID) field specified the endpoint for + which to deliver the packet. The width of this field is + configurable, the values of this field is chosen by the endpoints at + _flow allocation_. It can be thought of as an ephemeral port. + +--- +Changelog: + +2019 09 05: Initial version.
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