IPv6 Datagram Extension Headers
After the mandatory main header in an IPv6 datagram, one or more extension headers may appear before the encapsulated payload. These headers were created in an attempt to provide both flexibility and efficiency in the creation of IPv6 datagrams. All the fields that are needed for only special purposes are put into extension headers and placed in the datagram when needed. This allows the size of the main datagram header to be made small and streamlined, containing only those fields that really must be present all the time.
There is often confusion regarding the role of extension headers, especially when compared to datagram options. The IPv4 datagram had only one header, but it included a provision for options, and ...
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