arp working over network

ipv4/definitions.go

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+package ipv4
+
+const (
+	sizeHeader = 20
+)
+
+// ToS represents the Traffic Class (a.k.a Type of Service).
+type ToS uint8
+
+// DS returns the top 6 bits of the IPv4 ToS holding the Differentiated Services field
+// which is used to classify packets.
+func (tos ToS) DS() uint8 { return uint8(tos) >> 2 }
+
+// ECN is the Explicit Congestion Notification which provides congestion control and non-congestion control traffic.
+func (tos ToS) ECN() uint8 { return uint8(tos & 0b11) }
+
+// Flags holds fragmentation field data of an IPv4 header.
+type Flags uint16
+
+// IsEvil returns true if evil bit set as per [RFC3514].
+//
+// [RFC3514]: https://datatracker.ietf.org/doc/html/rfc3514
+func (f Flags) IsEvil() bool { return f&2000 != 0 }
+
+// DontFragment specifies whether the datagram can not be fragmented.
+// This can be used when sending packets to a host that does not have resources to perform reassembly of fragments.
+// If the DontFragment(DF) flag is set, and fragmentation is required to route the packet, then the packet is dropped.
+func (f Flags) DontFragment() bool { return f&0x4000 != 0 }
+
+// MoreFragments is cleared for unfragmented packets.
+// For fragmented packets, all fragments except the last have the MF flag set.
+// The last fragment has a non-zero Fragment Offset field, so it can still be differentiated from an unfragmented packet.
+func (f Flags) MoreFragments() bool { return f&0x8000 != 0 }
+
+// FragmentOffset specifies the offset of a particular fragment relative to the beginning of the original unfragmented IP datagram.
+// Fragments are specified in units of 8 bytes, which is why fragment lengths are always a multiple of 8; except the last, which may be smaller.
+// The fragmentation offset value for the first fragment is always 0.
+func (f Flags) FragmentOffset() uint16 { return uint16(f) & 0x1fff }