If you are using a GigE camera, it (the camera) will use as much of the MTU as you allow it. This is 8000 by default, which requires JUMBO PACKET support on your network card.
If you have JUMBO enabled, and configured (typicall 8192 MTU), it will alocate the remaining 192 to any communications like internet access. This is probably not enough for good performance.
In order to make use of the network connection for something more that image delivery, you need to set an appropriate MTU size for the camera, so that it is not using all of the available bandwidth. If the camera is just a few megapixels, and not really high frame rate, you can safely set the MTU to 1024 (assuming you have jumbo packets support in the NIC).
This is also true if you are using two or more cameras. You will need to divide the 8000 MTU between all devices/connection you need to use.
You will know if you have set the value too low if the image shows black stripes (this is done in MAX),
