Router Memory

Memory Type Characteristics
ROM (read-only memory) Preprogrammed, non-writable memory containing the bootstrap startup program, an older, smaller-scale version of the operating system (IOS) software, and the Power-on Self-Test (POST) program
Flash Non-volatile but programmable memory containing the proprietary Cisco operating system (IOS) images
RAM (random access memory) Volatile memory containing the running operating system and current (unsaved) configuration information
NVRAM (non-volatile RAM) Non-volatile but persistent memory that contains the backup copy of the startup configuration (startup-config) file and virtual configuration register

The contents of non-volatile memory (such as ROM, flash, and NVRAM) remain when the router is powered off (however, you must modify the configuration registry and NVRAM during password recovery). The contents of volatile memory (RAM) are lost when the router is powered down.

RAM - 1) running config 2) IOS zagruzhaetsia â RAM (obichno iz flash-pamiati)
nvram - startup config
rom - flash (bios), mozhno iz TFTP

Ios File System

copy flash tftp


tftp example in Windows:


to create a server
Router(config)# tftp-server flash gs7-k.9.17
show file systems


dir same as with Windows

more same as with Unix, to view content

delete, erase
cd to change directories


pwd to print the working directory


mkdir rmdir to create and delete directories
to upgrade IOS:
R1#show file info flash:c1841-ipbase-mz.124-1c.bin flash:c1841-ipbase-mz.124-1c.bin: type is image (elf) [] file size is 13937472 bytes, run size is 14103140 byte Runnable image, entry point 0x8000F000, run from ram

delete current IOS
R1#delete flash:c1841-ipbase-mz.124-1c.bin Delete filename [c1841-ipbase-mz.124-1c.bin]?[enter] Delete flash:c1841-ipbase-mz.124-1c.bin? [confirm][enter]

copy new ios from tftp:
R1#copy tftp://1.1.1.2//c1841-advipservicesk9-mz.124-12.bin/ flash:/ c1841-advipservicesk9-mz.124-12.bin

show flash


show ver - part of the show ver command, regarding Bootstrap(zagruzchik)


Cisco Discovery Protocol (CDP) is a proprietary layer 2 network protocol.
Cisco devices send CDP announcements to the multicast destination address 01-00-0c-cc-cc-cc (which is also used for other Cisco proprietary protocols such as VTP).
sh cdp
Corp#sh cdp neighbors Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge S - Switch, H - Host, I - IGMP, r - Repeater Device ID Local Intrfce Holdtme Capability Platform Port ID ap Fas 0/1 165 T I AIR-AP124 Fas 0 R2 Ser 0/1/0 140 R S I 2801 Ser 0/2/0 R3 Ser 0/0/1 157 R S I 1841 Ser 0/0/1 R1 Ser 0/2/0 154 R S I 1841 Ser 0/0/1 R1 Ser 0/0/0 154 R S I 1841 Ser 0/0/0 Corp#

Holdtime The amount of time the router will hold the information before discarding it if no more CDP packets are received.

sh cdp neighbors - packets aren’t passed through a Cisco switch
sh cdp neighbors detail - can be run on both routers and switches, and it displays detailed information about each device connected to the device you’re running the command on
show cdp entry * protocols


sh cdp traffic - to view cdp packets
by sh run and sh cdp nei it is possible to view topology
sh sessions - to see the connections made from your router to a remote device.
Ctrl+Shift+6, then X - to to come back to original router console
disconnect - to end a session from a local device
exit - to end a session from a remote device
There are two ways to resolve hostnames to IP addresses: ip host host_name tcp_port_number ip_address - to link ip address to any name (up to 8 IPs)


sh hosts - provides information on temrorary dns entries and permanent name-to-address mapping created during the ip host command

perm in the Flags column means that the entry is manually configured, temp it was resolved by DNS

no ip domain lookup - to stop resolving



to use DNS server:
sh processes cpu