Nonvolatile RAM

As with all Cisco devices, there must be some place to store the configuration while the device is powered down. Almost all Cisco devices use Nonvolatile RAM (NVRAM) for this purpose. However, the Native IOS Mode MSFC is somewhat unique in that it maintains two sets of NVRAM configurations:

• The VLAN database

• The local switch configuration

Although it might appear strange at first to have two different sorts of NVRAM information, it makes complete sense upon closer inspection. Consider that each NVRAM repository is storing a different type of information. The VLAN database contains information that is global to the entire network. As information is added to this list, it should be immediately (or almost immediately) saved and shared through the entire VTP domain. (Assume that the current switch is a VTP server; for more information, see Chapter 12, "VLAN Trunking Protocol." ) Also, as VTP advertisements are received from other devices, they should immediately be saved (recall that the definition of a VTP server requires that all VLANs be saved to NVRAM). On the other hand, the switch configuration is locally significant. Furthermore, these normal IOS configuration statements are only supposed to be saved when the user enters the copy run start or write memory commands. After all, one of the benefits to the IOS is that you can make all the changes you want and return to the exact place you started from by merely rebooting the box (assuming that you did not save the new configuration).

Therefore, rather than trying to interleave the two sets of data, two completely different stores are maintained. The VLAN database holds globally significant information that gets saved right away (as it would under the XDI/CatOS interface). The switch configuration stores locally significant information only when the user enters some form of a save command.

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