adjacent layer interaction – on one computer, this is one layer providng information to the next higher layer. Software performing a higher function will request that a lower function perform a task.
boot field – the lower-order 4 bits of the configuration register. They tell the router what to load. 0x0=ROMMON, 0x1=RXBOOT, or a full-blown IOS image
configuration register – a 16-bit number set with “config-register”. Sets low-level features related to accessing the router, and how the router will behave once powered up.
enhanced editing – at the IOS CLI, this refers to special keystrokes that can make using the CLI easier.
LxPDU – layer x PDU – a PDU used at a specific layer of the OSI model, where “x” refers to the layer.
PDU – protocol data unit – refers to a chunk of data, including its headers, at a specific layer of the OSI model.
ROMMON – stored in ROM, it is an operating system used instead of IOS, either because the router’s main IOS is unloadable, or the router requires low-level diagnostics.
RXBOOT – stored in ROM, it is an operating sytem used instead of IOS, generally because the main IOS isn’t loading. With RXBOOT, you have basic IP connectivity and can load a new image.
same-layer interaction – one computer talking to another at the same layer of the OSI model. The protocol each layer uses has a header telling each computer what the other wants to do.
terminal history – a command buffer on a IOS devices, allowing you to hit the up/down arrows to cycle through commands previously entered into the router.