I am writing a client-server python application, a part of which is using UDP Multicast to communicate. And my current concern is about fragmentation.
RFC 791 (page 24) says:
Every internet module must be able to forward a datagram of 68 octets without further fragmentation. This is because an internet header may be up to 60 octets, and the minimum fragment is 8 octets.
By reading the above i understand that we can have an Application Layer PDU, 8 bytes of size, that can pass without fragmentation.
On Packet Tracer(an application where you can configure Routers in a Virtual environment), the minimum allowed MTU is 64 (see image below). This means that the Application Layer PDU guaranteed size can be 4 bytes?
I may not have understood this correctly, that's why i would like your help.
The question is: What should be the size of the Application Layer PDU, so that the IP packet that contains it can pass without being fragmented? 4 or 8 bytes?