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@@ -1,2 +1,51 @@
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-// Package waterutil provides utility functions for interpreting MAC farme headers and IP packet headers. It defines some constants such as protocol numbers and ethernet frame types. Use waterutil along with package water to work with TUN/TAP interface data.
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+/*
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+Package waterutil provides utility functions for interpreting TUN/TAP MAC farme headers and IP packet headers. It defines some constants such as protocol numbers and ethernet frame types. Use waterutil along with package water to work with TUN/TAP interface data.
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+
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+Frames/packets are interpreted in following format (as in TUN/TAP devices):
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+
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+TAP - MAC Frame:
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+ No Tagging
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+ +-----------------------------------------------------------------------------
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+ | Octet |00|01|02|03|04|05|06|07|08|09|10|11|12|13|14|15|16|17|18|19|20|21|...
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+ +-----------------------------------------------------------------------------
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+ | Field | MAC Destination | MAC Source |EType| Payload
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+ +-----------------------------------------------------------------------------
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+
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+ Single-Tagged -- Octets [12,13] == {0x81, 0x00}
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+ +-----------------------------------------------------------------------------
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+ | Octet |00|01|02|03|04|05|06|07|08|09|10|11|12|13|14|15|16|17|18|19|20|21|...
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+ +-----------------------------------------------------------------------------
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+ | Field | MAC Destination | MAC Source | Tag | Payload
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+ +-----------------------------------------------------------------------------
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+
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+ Double-Tagged -- Octets [12,13] == {0x88, 0xA8}
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+ +-----------------------------------------------------------------------------
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+ | Octet |00|01|02|03|04|05|06|07|08|09|10|11|12|13|14|15|16|17|18|19|20|21|...
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+ +-----------------------------------------------------------------------------
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+ | Field | MAC Destination | MAC Source | Outer Tag | Inner Tag | Payload
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+ +-----------------------------------------------------------------------------
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+
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+TUN - IPv4 Packet:
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+ +-----------------------------------------------------------------------------------------------------------------+
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+ | Offsets | Octet | 0 | 1 | 2 | 3 |
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+ | Octet | Bit |00|01|02|03|04|05|06|07|08|09|10|11|12|13|14|15|16|17|18|19|20|21|22|23|24|25|26|27|28|29|30|31|
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+ +-----------------------------------------------------------------------------------------------------------------+
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+ | 0 | 0 | Version | IHL | DSCP | ECN | Total Length |
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+ +-----------------------------------------------------------------------------------------------------------------+
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+ | 4 | 32 | Identification | Flags | Fragment Offset |
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+ +-----------------------------------------------------------------------------------------------------------------+
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+ | 8 | 64 | Time To Live | Protocol | Header Checksum |
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+ +-----------------------------------------------------------------------------------------------------------------+
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+ | 12 | 96 | Source IP Address |
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+ +-----------------------------------------------------------------------------------------------------------------+
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+ | 16 | 128 | Destination IP Address |
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+ +-----------------------------------------------------------------------------------------------------------------+
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+ | 20 | 160 | Options (if IHL > 5) |
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+ +-----------------------------------------------------------------------------------------------------------------+
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+ | 24 | 192 | |
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+ | 30 | 224 | Payload |
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+ | ... | ... | |
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+ +-----------------------------------------------------------------------------------------------------------------+
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+
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+*/
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package waterutil
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package waterutil
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Song Gao