Question

explain what is condition for ip fragmentation to occur.

explain what is fields in ip packet header involved in ip fragmentation

Answer 1

Answer :- IP fragmentation happens in case where a router receives a protocol data unit(PDU) larger than the next hop's MTU(Maximum Transmission Unit). MTU is the maximum amount of data that a link layer frame can carry.

The following IP packet header fields are involved in IP fragmenttion-
1. Identification
2. Flags(DF and MF)
3. Fragment offset
4. Total length

Identification :- When a datagram is fragmented, the identification is the same in all fragments.

DF bit is set :- Datagram cannot be fragmented and must be discarded if MTU is too small.
MF bit set :- This datagram is part of a fragment and an additional fragment follows this one.

Fragment offset :- Offset of the payload of the current fragment in the original datagram.

Total Length :- Total length of the current fragment.