Editing IPv6 (section)

===Simplified processing by routers===
The packet header in IPv6 is simpler than the IPv4 header. Many rarely used fields have been moved to optional header extensions. The IPv6 packet header has simplified the process of packet forwarding by [[Router (computing)|routers]]. Although IPv6 packet headers are at least twice the size of IPv4 packet headers, processing of packets that only contain the base IPv6 header by routers may, in some cases, be more efficient, because less processing is required in routers due to the headers being aligned to match common [[Word (computer architecture)|word sizes]].<ref name=rfc2460/><ref name=rfc1726/> However, many devices implement IPv6 support in software (as opposed to hardware), thus resulting in very bad packet processing performance.<ref>{{cite web|title=IPv6 Security Assessment and Benchmarking|first=E.|last=Zack|date=July 2013|url=http://www.ipv6hackers.org/meetings/ipv6-hackers-1}}</ref> Additionally, for many implementations, the use of Extension Headers causes packets to be processed by a router's CPU, leading to poor performance or even security issues.<ref name="draft-gont-v6ops-ipv6-ehs-packet-drops-03">{{Cite web |last=Gont |first=F. |date=March 2016 |title=Operational Implications of IPv6 Packets with Extension Headers |url=https://datatracker.ietf.org/doc/html/draft-gont-v6ops-ipv6-ehs-packet-drops-03 |url-status=live |archive-url=https://web.archive.org/web/20231027170015/https://datatracker.ietf.org/doc/html/draft-gont-v6ops-ipv6-ehs-packet-drops-03 |archive-date=27 October 2023 |publisher=[[IETF]] }}</ref>

Moreover, an IPv6 header does not include a checksum. The [[IPv4 header checksum]] is calculated for the IPv4 header, and has to be recalculated by routers every time the [[time to live]] (called [[hop limit]] in the IPv6 protocol) is reduced by one. The absence of a checksum in the IPv6 header furthers the [[end-to-end principle]] of Internet design, which envisioned that most processing in the network occurs in the leaf nodes. Integrity protection for the data that is encapsulated in the IPv6 packet is assumed to be assured by both the [[link layer]] or error detection in higher-layer protocols, namely the [[Transmission Control Protocol]] (TCP) and the [[User Datagram Protocol]] (UDP) on the [[transport layer]]. Thus, while IPv4 allowed UDP datagram headers to have no checksum (indicated by 0 in the header field), IPv6 requires a checksum in UDP headers.

IPv6 routers do not perform [[IP fragmentation]]. IPv6 hosts are required to do one of the following: perform [[Path MTU Discovery]], perform end-to-end fragmentation, or send packets no larger than the default [[maximum transmission unit]] (MTU), which is 1280 [[octet (computing)|octets]].