Booting and Memories

ROM: Read Only Memory. bootstrap startup program. operating system software. power on diagnostic test program.

POST: Power On Self Test

Flash Memory: ios image here. erasable reprogrammable rom.

RAM: Random Access Memory. stores operational info such as routing/switching tables and running config file. it is lost when router powered down or rebooted.

NVRAM: non volatile ram. holds router startup config file. contents are not lost on rebooting. NV(never)



r1(config)# cdp run

cdp run … cdp is usually turned on but if it’s not the command above turns it on

r1(config)# show cdp neighbors

shows you what it’s plugged into

Only cisco devices.


Link Layer Discovery Protocol


r1(config)# lldp run

This one is not usually turned on so you have to manually turn it on.

shows you what it’s plugged into

All devices. IEEE standard.




Remote Admin Security

  1. limit active vty ports
  2. generate individual user/password (login local)
  3. limit active time
  4. disable TELLNET / Enable SSH
    1. Needs Hostname
    2. Needs Domain Name
    3. Generate Key
    4. SSH ver 2
    5. Use SSH Exclusively
  5. AAA server to centralize users
  6. ACL Access Lists


r2(config)# hostname r2

r2(config)# ip domain-name ccna.class

r2(config)# crypto key generate rsa

r2(config)# r2.ccna.class

r2(config)# line vty 0 1

r2(config-line)# transport input ssh


logging in



ssh -l name x.x.x.x


VLAN Trunking (class notes)

Trunking is the process of creating logical connection between two physically connected switches allowing frames to flow between them.

Members of same VLAN communicate when physically attached to different switches.

ISL: cisco proprietary. encapsulates the entire frame before sending it across the trunk. results in greater overhead than ieee 802.1q. does not recognize native vlan

dot1q: industry standard. does not encapsulate frame. inserts 4byte value with vlan id in ethernet header. recognize native vlan.

native vlan: default vlan. usually vlan 1.

Dot1Q will not put 4byte value into ethernet header if frame is destined for native vlan. When remote switch receives an untagged frame and it knows it is destined to native vlan frame is forwarded to ports belonging to that vlan.




VLANS – (class notes)

Vlans help us group hosts by whatever category.

Vlans allow you to increase security by hiding logical group of hosts from everyone else you want.

Prevents broadcast storms.

Broadcast storms slow network performance down a little, little more, little more and prevents basic switching functions.

IP address run at layer three.

Lab Example


If your on host one and you

host1# show cdp neighbor

You’ll see your physical connections.


Log on to switch1

switch1# show cdp neighbor

See all of your connections.

show vlan will give you info you need.


switch1# config t

switch1#(config) #int fast 0/2

switch1(config-if)# switchport access vlan 24

this is creating vlan 24

switch1#(config) #int fast 0/4

switch1(config-if)# switchport access vlan 24

switch1#show vlan brief

You’ll see it was created