Editing IP fragmentation (section)

== Impact on network forwarding ==
When a network has multiple parallel paths, technologies like [[Link aggregation|LAG]] and [[Cisco Express Forwarding|CEF]] split traffic across the paths according to a [[Hash function|hash algorithm]]. One goal of the algorithm is to ensure all packets of the same [[Traffic flow (computer networking)|flow]] are sent out the same path to minimize unnecessary [[Out-of-order delivery|packet reordering]].

IP fragmentation can cause excessive retransmissions when fragments encounter [[packet loss]] and reliable protocols such as TCP must retransmit all of the fragments in order to recover from the loss of a single fragment.<ref>{{cite web|author=Christopher A. Kent, Jeffrey C. Mogul|url=http://www.cs.binghamton.edu/~nael/classes/cs528/fragment.pdf|title=Fragmentation Considered Harmful}}</ref> Thus, senders typically use two approaches to decide the size of IP packets to send over the network. The first is for the sending host to send an IP packet of size equal to the MTU of the first hop of the source-destination pair. The second is to run the Path MTU Discovery algorithm<ref>{{citation |rfc=1191 |title=Path MTU Discovery |date=November 1990 |last1=Deering |first1=Steve E. |last2=Mogul |first2=Jeffrey }}</ref> to determine the path MTU between two IP hosts so that IP fragmentation can be avoided.

{{as of|2020}}, IP fragmentation is considered fragile and often undesired due to its security impact.<ref>{{cite IETF |rfc=8900 |title=IP Fragmentation Considered Fragile |date=September 2020}}</ref>