Layer 7 – Application
·       Telnet can test if this level is working properly
Layer 6 – Presentation
Layer 5 – Session
Layer 4 – Transport
·       windowing, UDP, segments
·       TCP, ACK, SYN
Layer 3 – Network
·       Router(DTE), IP address, packets, routing
·       IP, ARP, Clock required on DCE devices, drops DHCP broadcast on export by default, ICMP
·       Routers update MAC source/destination every hop
·       Cannot have same subnet on a single router, must have same subnet on connected routers
·       Use IP to forward traffic
·       Router use power switch on back on back
·       ip route (default routes are set on routers)
·       show cdp neighbor detail
Layer 2 – Data Link
·       Switch, MAC address, flood, multiple collision domains, frames
·       Switches forward broadcast and multicast traffic, they basically only filter by MAC I believe
·       Switches use microsegmentation to split up the ports (avoiding collisions by having more collision domains)
·       HDLC default (on routers), PPP
·       Use MAC to forward traffic
·       Switch just plug in, no power switch
·       ip default-gateway (is set on switches)
·       show cdp neighbor
Layer 1 – Physical
·       Hub,  Repeater, Single Collision domain

FF-FF-FF-FF-FF-FF first time ARP to destination that MAC is not known

FTP – TCP Port 20 and 21
SMTP – TCP Port 25
Telnet TCP – 23 – show sessions, resume 4, disconnect 3
DNS TCP & UDP - 53
·       DHCPDISCOVER (layer 3 broadcast)
·       DHCPACK

                  H               S                R                W

H               C                C                S                S

S               C                C                S                S

R               S                S                C                C

W              S                S                C                C

H = Hub
S = Switch
R = Router
W = Workstation

C = Crossover Cable
S = Strait Through Cable


Class A: 1-126 mask, network bits 8, host bits 24, private range, 22 borrow bits loopback etc...
Class B: 128-191 mask, network bits 16, host bits 16, private range, 14 borrow bits
Class C: 192-223 mask, network bits 24, host bits 8, private range, 6 borrow bits
Class D: 224-239 Multicast
Class E: 240-255 Future use

A simiple summary of the above is as follows
A 1-126 10.x.x.x
B 128-191 172.16-172.31.x.x
C 192-223 192.168.x.x


cdp is proprietary protocol to Cisco, cdp update packet has platform and device identifiers
no cdp run -  disables cdp globally (whole device, all interfaces)
no cdp enable - disables on a specific interface
show cdp traffic – packet checksum errors
show cdp neighbors (detail)
show cdp entry * = show cdp neighbors detail – device platform
show cdp interface – frequency, encapsulation type


Configuration Register – Boot field is the lowest 4 bits
From config mode: config, config-register 0x2102, end
From rommon mode: rommon 1> confreg 0x2102
0x2102 – Default (flash)
0x2100 – Rommon
0x2142 – Bypass startup for pw recovery
Normal Boot: Flash, TFTP, ROM (Rommon)
POST, IOS, Config

running-config: RAM
startup-config: NVRAM
IOS: Flash
Minimal boot helper: ROM

show version
show flash – amount of memory and where IOS stored

User EXEC > enable //in config mode: line console 0, password cisco, login
Privilege EXEC # configure terminal //in config mode: enable password cisco, or enable secret cisco
Global EXEC (config)#

Telnet/VTY Password: //in config mode: line vty 0 4, password cisco, login, transport input ssh

service password-encryption

In configuration mode(config)
username adam privilege 15 secret adam //if did password adam then not encrypted
line con 0
login local

Determine broadcast storm, no buffer and ignored
HDLC is default
PPP and PAP is for connecting Cisco to non Cisco equipment

access port - carries traffic for a single vlan, straight-through cable to connect a device, connects to an end-user workstation to a switch
trunk port - carries traffic for a multiple vlan, 802.1q to identify traffic from different vlans, facilitates intervlan communications when connected to a layer 3 device

PSTN - Packet Switched
ATM - Point to Point
Leased Line - Cell Switched
Frame Relay - Circuit Switched

802.11b – 11mbps
802.3ab 802.3z – Gigabit
ISL & 802.1Q – configurable encapsulation

Extended ping, trace, traceroute
Order of reliability: OSPF, RIP, Directly connected…
Service timestamps
Terminal monitor – telnet session receive console messages
Types of flow control – congestion avoidance, buffering, windowing


1) Say no to entering setup mode

2) Enter Privilege EXEC mode
Router> enable

3) Enter Global EXEC mode
Router# configure terminal

4) Set the Privilege EXEC password
Router(config)# enable secret cisco

5) Set the User EXEC password
Router(config)# line console 0
Router(config-line)# password cisco
Router(config-line)# login
Router(config-line)# logging synchronous
Router(config-line)# exit

6) Set the Telnet password
Router(config)# line vty 0 4
Router(config-line)# password cisco
Router(config-line)# login
Router(config-line)# logging synchronous
Router(config-line)# exit


NOTES: On the Telnet and Console settings if you set 'no login' it doesn't disable logins it means people can login without a password
You can set 'exec-timeout 10 0' to set the timeout before requires a login again.  'exec-timeout 0 0' would be to never log out if idle
Depending on the Router/Switch you may also need to configure line aux 0

7) Set the login banner (optional)
Router(config)# banner motd @

8) Give the Router a different hostname (optional)
Router(config)# hostname R1

9) Prevent the router from trying to DNS improperly typed commands
R1(config)# no ip domain-lookup

10) Encrypt all current and future passwords
R1(config)# service password-encryption
R1(config)# exit

11) Save/Commit the configuration
R1# copy running-config startup-config

Note: You can also use the command 'wr' to commit the configuration

Other: Command 'wr e' would do a write erase on the startup config, this is equivalent to 'erase startup-config'.  You'd only want to do this if you want to start over on the router.
This command reboots the router 'reload'.

128  64  32  16  8  4  2  1


Also try to find a copy of Packet Tracer, helps a lot with practicing simulations. Google 'PacketTracer531_setup.exe'