<|im_start|>system
You are a helpful AI assistant.<|im_end|>
<|im_start|>user
What happens if you send a packet that is bigger than the MTU?<|im_end|>
<|im_start|>assistant
When you send a packet that is bigger than the Maximum Transmission Unit (MTU) of a network, the packet must be fragmented before transmission. Fragmentation is the process of breaking the packet into smaller pieces to fit within the MTU size of the network.

Here's what happens when a packet exceeds the MTU:

1. The sender or an intermediate router identifies that the packet size exceeds the MTU of the network.
2. The packet is broken down into smaller fragments, each of which is within the MTU limit.
3. Fragmentation is typically performed at the IP layer, and each fragment has its own IP header with relevant information, such as the source and destination IP addresses, as well as a fragmentation offset and flags.
4. The fragments are transmitted separately over the network.
5. When the fragments reach the destination, they are reassembled into the original packet by the receiving device. This process is called reassembly.
6. If any of the fragments are lost or corrupted during transmission, the entire packet may need to be retransmitted, as IP fragmentation does not provide error correction or retransmission capabilities.

It's important to note that fragmentation can lead to performance issues and increased overhead. To avoid or minimize fragmentation, it is recommended to use Path MTU Discovery (PMTUD) to determine the smallest MTU along the path between the sender and receiver and adjust the packet size accordingly. Additionally, some protocols like TCP have built-in mechanisms to adjust the segment size dynamically to avoid fragmentation.<|im_end|>
<|im_start|>user
What is the current largest MTU packet size and how can this be upscaled in the future?<|im_end|>
<|im_start|>assistant
The largest MTU that can reliably used on the internet is 1500 bytes. Some networks support jumbo frames which commonly raise the MTU to 9000 bytes. Certain technologies such as DSL or VPNs may have smaller maximum MTU sizes than 1500.<|im_end|>
<|im_start|>user
Sending a packet that is larger than the maximum size allowed on a network can cause issues along the distribution pipeline. The packet will get split up into smaller chunks, which slows down the network and increases latency. Additionally, splitting and reassembling packets requires more overhead, using up network resources and bandwidth. This can lead to data loss, congestion, and delays. Furthermore, continuously forcing very large packets through can make it harder for the network to determine the optimal packet size for that path. To ensure the best network performance, responsiveness, and reliability, it's best to keep packets around the MTU size advertised for the network path being used and to avoid excessively oversized packets.<|im_end|>
<|im_start|>assistant
If packet size exceeds the MTU this will result in packet fragmentation. This introduces overhead and latency to the data transmission in a best case scenario and application failure in the worst case. If any of the fragmented packets are lost the entire original oversized packet must be retransmitted resulting in additional delay and overhead. It is best practice to keep packets within the MTU size. If larger packets are needed you should speak with your network operator to see if jumbo frames can be enabled.<|im_end|>