General network concerns

Apart from routing, there are a few additional networking components that tend to trip up even some advanced server administrators.

Path MTU and MSS

Maximum transmission unit (MTU) problems are some of the most difficult problems to identify. In part, this is due to the odd symptoms that arise when an MTU incompatibility is present. During such a condition, some traffic will seem to function without a problem, whereas other traffic will inexplicably fail.

MTU is the largest packet that can traverse a network link intact. In the event that a larger packet transfer is attempted, it will either fail to reach the remote endpoint, or a fragmentation request will be sent back to the sender. This request tells the previous hop that the packet was too big and specifies how big the next packet should be:

In general, when MTU problems exist, traffic with typically small packets will work without any issue. SSH, for example, sends many small packets during console sessions,...