This means that fragmentation cannot be performed on other networks, except the source. In IPv6, data can only be fragmented on the source host. The final fragment is allowed to carry data that isn’t a multiple of 8 bytes as there won’t be any more fragments.Įven though most of the header fields remain the same, IP fragmentation in IPv6 works a bit differently than IPv4. This means that the previous fragment has to be a multiple of 8 bytes. The offset value has to be the number of 8-byte blocks of data. If an IP packet containing data worth 800 bytes is split into two equal pieces/fragments, each carrying 400 bytes, then the fragment offset of the 1st fragment is 0, while the other one is 50 (400/8). In the following fragments, the value is offset of fragmented data from the starting of the data in the initial fragment (0 offset), in 8-byte blocks (also known as octawords). The offset in the first fragment is 0 since the data in this fragmented packet and the original one start at the same place. This is then used for reassembling the data from all fragments (arrived or not). The field Fragment Offset (total 13 bits) is utilized for indicating the initial data position in the fragment, in relation to the starting data of the original IP packet.
#PINGPLOTTER IPV6 CODE#
Errors should be sent to the sender in this case, like type 3 ICMP error: ‘Destination Unreachable’, code 4: ‘Fragmentation required, and DF set.’ If in the original packet, the Don’t Fragment flag is set, then this would prevent fragmentation and result in packets required to be discarded. More Fragments (MF) set to 1. All the bits in this field of the last IP packet will be set 0, exactly like the original IP packet (unless it’s a fragment). However, the final fragment will have the field’s third bit i.e. This simply means that the same ID can be utilized even when the source, protocol, and destination of the fragmented packets are not the same.Įxactly like the original IP packet, the first reserved bit of the Flags field (total 3 bits), and the second one, the Don’t Fragment (DF) bit will both be unset (0). The Protocol field, having the original packet’s value, enables the destination to differentiate among the various packets’ fragments coming from the same source. The Identification field (16 bits) contains a unique ID number which is a mixture of source and destination IP addresses. All these fragments will have values significantly different as compared to the original IP packet: The operation of fragmentation relies on three IP header fields (a total of 32 bits). The fragmentation and the reassembling process have various IP header fields involved that are set into pieces/fragments. Transport layer protocols to downsize overheads and be ignorant of the underlying network architecture.
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