The Importance of Fragmentation in Routing: Managing Packet Transmission Across Different MTU Sizes

A router may have to fragment a packet when forwarding it from one medium to another medium that has a smaller _______________ .

Maximum Transmission Unit (MTU)

A router may have to fragment a packet when forwarding it from one medium to another medium that has a smaller Maximum Transmission Unit (MTU).

MTU refers to the maximum size of a packet that can be transmitted over a particular network medium without being fragmented. Different network technologies have different MTU sizes. For example, Ethernet typically has an MTU of 1500 bytes, while some WAN technologies like PPPoE (Point-to-Point Protocol over Ethernet) may have a smaller MTU, such as 1492 bytes.

When a router receives a packet from a source network with an MTU larger than the destination network’s MTU, it needs to break the packet into smaller fragments that fit the destination MTU. Fragmentation involves dividing the original packet into smaller segments and adding headers to each fragment so that they can be reassembled at the destination.

Fragmentation can introduce overhead and potential issues with network performance and reliability. Therefore, routers try to avoid fragmentation by default. However, if a router receives a packet that exceeds the destination network’s MTU, it will fragment the packet to ensure successful transmission over the smaller MTU network.

It is worth noting that some network protocols, like IPv6, discourage fragmentation and rely on end-to-end path MTU discovery, where devices along the path automatically adjust their MTU to avoid the need for fragmentation. However, in situations where fragmentation is necessary, routers have the responsibility to perform it to ensure successful packet delivery from one medium to another with a smaller MTU.

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