10.3.3.1. MTU Packet 
We work with an MTU size of 1500 bytes as standard. An overview is
provided below for greater clarity as regards how the packet is assembled:
|--------------------------------------------------------------|
| Ethernet | IPv4 | UDP | Data | Ethernet checksum|
|--------------------------------------------------------------|
14 bytes 20 bytes 8 bytes x bytes 4 bytes
\ (w/o options) /
\_____________________________/
|
MTU
Represented differently:
1472 bytes payload of ICMP protocol (transport layer)
+ 8 bytes ICMP header (transport layer)
+ 20 bytes IPv4 header (network layer)
-------------
= 1500 bytes (Ethernet payload) /* for us this is the defined MTU value
+ 14 bytes (data link layer header)
+ 4 bytes (frame check sequence)
-------------
= 1518 bytes (complete Ethernet frame)
If the MTU size is not permitted to exceed 1500, the OpenScape
4000 can only send a maximum of 1472 bytes as payload for UDP.
In case of a protocol other than UDP (8 bytes), e.g. TCP (20 bytes),
the size of the header changes and consequently the resulting size of
the payload.
It is therefore okay if a packet length of 1510 bytes, for example,
is displayed in a Wireshark Trace. It must then be calculated what the
actual length (less overhead) is.
INFO:
The MSS Clamping procedure can also be used for changing the MTU
packet size. MSS Clamping is used in the WAN and automatically adapts
the TCP packet size in dialog between the router and the OpenScape 4000
host or access point.