Tylogix.com -> Networking Definitions

The purpose of this page is to record networking term definitions. It is a work in progress.

Family	Definition	Explanation
Cisco Hardware	ROM Read-Only Memory	Read-Only Memory. ROM stores the router’s bootstrap startup program, operating system software, and power-on diagnostic test programs (the POST)
Cisco Hardware	FLASH	On a Cisco router, Flash stores the Cisco Internetwork Operating System (IOS) images. Flash is really a form of erasable and reprogrammable ROM. Flash memory content is retained by the router on power-down or reload.
Cisco Hardware	NVRAM Non-Volatile Random-Access Memory	On a Cisco router, NVRAM stores the startup configuration file. If NVRAM is empty when the router reloads, the router will prompt to enter setup mode.
Cisco Hardware	RAM Random-Access Memory	On a Cisco router, RAM stores operational information such as routing tables and the running configuration file. RAM contents are lost when the router is powered down or reloaded.
Frame Relay	BE - Excess Burst	Amount of data above the CBIR up to the access rate which frames may use to burst with no guarantee. Frames are also marked as discard eligible (DE) and cannot exceed the access rate of the link.
Frame Relay	CBIR - Committed Burst Information Rate	Negotiated maximum which a frame is allowed to burst above the CIR. Frames are marked as discard eligible (DE). It cannot exceed the access rate of the link.
Frame Relay	CIR - Committed Information Rate	The capacity through the local loop guaranteed by the provider. Customers normally choose a CIR lower than the access rate to allow them to take advantage of bursts.
Frame Relay	DLCI - Data Link Connection Identifier	Virtual Circuits (VC's) are identified by DLCIs, and the DLCI values are assigned by the Frame Relay service provider. Frame Relay DLCIs have local significance and no significance beyond the single link. A DLCI identifies a VC to the equipment at an endpoint.
Frame Relay	Inverse ARP	Inverse Address Resolution Protocol (ARP) obtains Layer 3 addresses of other stations from Layer 2 addresses, such as the DLCI in Frame Relay networks (which is the reverse of what ARP does). It is primarily used in Frame Relay and ATM networks, where Layer 2 addresses of VCs are sometimes obtained from Layer 2 signalling, and the corresponding Layer 3 addresses must be available before these VCs can be used.
Frame Relay	LMI - Local Management Interface	LMI is a keep-alive mechanism that provides status information about Frame Relay connections between the router (DTE) and the Frame Relay switch (DCE). Three types of LMIs are supported by Cisco routers: Cisco, ANSI, and q933a.

Family

Definition

Explanation

TFTP Methods

How to backup an IOS Image

Step 1: show flash

-> will show contents of Flash memory, including IOS image - something like

c1841-ipbase-mz.123-14.T7.bin

for an 1841 model Cisco router. We need the name of that IOS image to copy it.

Step 2: copy flash: tftp

-> will ask the source file name (in this case, the IOS image we have just figured out)

-> will ask the remote host IP address (address or name of remote host)

->will ask to confirm destination file name is the same - use ENTER to confirm.

TFTP Methods

How to upload a new IOS Image

Step 1: copy tftp flash:

-> will ask the remote host IP address (address or name of remote host)

-> will ask the source file name (in this case, the IOS image we have just figured out - if you want to refresh)

->will ask to confirm destination file name is the same - use ENTER to confirm.

By default, the router bootup sequence loads the first Cisco IOS image listed in flash. One way to make

sure that the router loads the new image is to configure the boot system flash command. On R2, enter

the following command:

R2(config)#boot system flash c1841-ipbasek9-mz.124-12.bin

This command is now part of the running configuration. However, the running configuration must also be

saved to NVRAM; otherwise, the configuration is overwritten the next time you reload the router.

R2(config)#end

R2#copy running-config startup-config

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