Do you experience intermittent performance problems, particularly at branch offices? Do some applications “not work” and then self-resolve before you can address them? Limitations in path MTU may be the cause of your problems!
In today's networking environment, you may encounter situations where your traffic passes through a path with an MTU that is lower than the standard 1500 bytes, for example if you are using a PPPoE DSL or an IPSec VPN. If you are aware of a limitation in the MTU along a path you should use the IP MTU command on the interface facing this path to limit the MTU. This should be done as close as possible to the traffic source so that messages are sent back immediately informing the client of the limitations while reducing the chances of them being lost of ignored.
These network settings will result in packet fragmentation. Since TCP is a stream oriented protocol which handles packet re-ordering, as well as, the retransmission of lost packets, it should not suffer packet loss directly tied to fragmentation but will suffer a performance degradation.
However, on the other hand, UDP being a message oriented protocol, it does not have a built-in reordering or retransmitting mechanism, so fragmentation should be avoided. Further, when your traffic flows through devices that you have no control over nor visibility on such as sending traffic over the internet, then this should be avoided at all cost.