99 lines
3.3 KiB
ReStructuredText
99 lines
3.3 KiB
ReStructuredText
.. only:: comment
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© Crown-owned copyright 2024, Defence Science and Technology Laboratory UK
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.. _internal_frame_processing:
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Internal Frame Processing
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=========================
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Inbound
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-------
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At the NIC
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^^^^^^^^^^
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When a Frame is received on the Node's NIC:
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- The NIC checks if it is enabled. If so, it will process the Frame.
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- The Frame's received timestamp is set.
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- The Frame is captured by the NIC's PacketCapture if configured.
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- The NIC decrements the IP Packet's TTL by 1.
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- The NIC calls the Node's ``receive_frame`` method, passing itself as the receiving NIC and the Frame.
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At the Node
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^^^^^^^^^^^
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When ``receive_frame`` is called on the Node:
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- The source IP address is added to the ARP cache if not already present.
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- The Frame's protocol is checked:
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- If ARP or ICMP, the Frame is passed to that protocol's handler method.
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- Otherwise it is passed to the SessionManager's ``receive_frame`` method.
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At the SessionManager
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^^^^^^^^^^^^^^^^^^^^^
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When ``receive_frame`` is called on the SessionManager:
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- It extracts the key session details from the Frame:
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- Protocol (TCP, UDP, etc)
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- Source IP
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- Destination IP
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- Source Port
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- Destination Port
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- It checks if an existing Session matches these details.
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- If no match, a new Session is created to represent this exchange.
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- The payload and new/existing Session ID are passed to the SoftwareManager's ``receive_payload_from_session_manager`` method.
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At the SoftwareManager
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^^^^^^^^^^^^^^^^^^^^^^
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Inside ``receive_payload_from_session_manager``:
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- The SoftwareManager checks its port/protocol mapping to find which Service or Application is listening on the destination port and protocol.
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- The payload and Session ID are forwarded to that receiver Service/Application instance via their ``receive`` method.
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- The Service/Application can then process the payload as needed.
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Outbound
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--------
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At the Service/Application
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^^^^^^^^^^^^^^^^^^^^^^^^^^
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When a Service or Application needs to send a payload:
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- It calls the SoftwareManager's ``send_payload_to_session_manager`` method.
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- Passes the payload, and either destination IP and destination port for new payloads, or session id for existing sessions.
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At the SoftwareManager
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^^^^^^^^^^^^^^^^^^^^^^
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Inside ``send_payload_to_session_manager``:
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- The SoftwareManager forwards the payload and details through to to the SessionManager's ``receive_payload_from_software_manager`` method.
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At the SessionManager
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^^^^^^^^^^^^^^^^^^^^^
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When ``receive_payload_from_software_manager`` is called:
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- If a Session ID was provided, it looks up the Session.
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- Gets the destination MAC address by checking the ARP cache.
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- If no Session ID was provided, the destination Port, IP address and Mac Address are used along with the outbound IP Address and Mac Address to create a new Session.
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- Calls `send_payload_to_nic`` to construct and send the Frame.
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When ``send_payload_to_nic`` is called:
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- It constructs a new Frame with the payload, using the source NIC's MAC, source IP, destination MAC, etc.
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- The outbound NIC is looked up via the ARP cache based on destination IP.
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- The constructed Frame is passed to the outbound NIC's ``send_frame`` method.
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At the NIC
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^^^^^^^^^^
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When ``send_frame`` is called:
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- The NIC checks if it is enabled before sending.
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- If enabled, it sends the Frame out to the connected Link.
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