UDP segment reassembly |NO seq num in UDP header|

[sarahr202]

Hi everybody

I hope you are doing fine. 

A quick question for you guys

Let say we have two host:

A------B

A wants to transfer data to B using UDP

Assume A  has a UDP segment of 10000  bytes to send to B

A chops down these 10000 bytes into each 1000 bytes chunk and sends total 10 packets to B, each carrying 1000 bytes as IP pay load.

B will wait for all the 10 packets, once all received, B ( ip layer) reassembles them into a UDP segment of 10000 bytes and gives it to UDP layer for processing.

1) UDP header has no seq number , so how does B determine all these packets belong to  a particular UDP segment ?

2) How does B knows that it has received the last packet belonging to a particular UDP segment and it is time to reassemble this last packet and give the reassembled UDP segment to UDP layer?

Thanks

[Giuseppe Larosa · Accepted solution]

Hello Sarah,

IPv4 header provides in this case the fragmentation and reassembly services, UDP just uses it being the upper layer protocol

last fragment has the M more fragments not set in the IPv4 header

Hope to help

Giuseppe

[sarahr202]

Thanks Giuseppe.