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A Cisco Cheatsheet: Commands and Snippets for bootstrapping, boilerplate, configuration, and hardening of Cisco routers and switches.

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Cisco Cheetsheet

Cisco CLI Reference, Howtos, and Tools

Warning, use at your own risk. I created these scripts with an educational mindset while studying for my CCNA

Quick Navigtation

Quick Snippets & Scripts

General Sections

Full Navigation

Basic Networking

Setup

Intialize

These commands wipe all config and reboot the device

erase startup-config
delete vlan.dat
reload

Note: Remeber to say "no" to saving running config on reload. If you say yes, running config will be saved and you wont be working with fresh config on reload.

Basic Switch Config

configure terminal
no ip domain-lookup
hostname S1
line console 0
logging synchronous
exit
banner motd $ Authorized Access Only! And Godzilla will beat Kong any day $
exit
copy running-config startup-config

Basic Router Config

configure terminal
no ip domain-lookup
hostname R1
line console 0
logging synchronous
exit
banner motd $ Authorized Access Only! And Godzilla will beat Kong any day $
exit
copy running-config startup-config

Basic Config with Password Security

pastable

configure terminal
no ip domain-lookup
hostname R1
line console 0
logging synchronous
exit
banner motd $ Authorized Access Only! And Godzilla will beat Kong any day $
exit
copy running-config startup-config
conf t
enable secret class
line console 0
password cisco
login
exit
line vty 0 4
password cisco
login
exit
service password-encryption
end
copy running-config startup-config

Basic Security

conf t
enable secret class
line console 0
password cisco
login
exit
line vty 0 4
password cisco
login
exit
service password-encryption
end

Configure SSH

show ip ssh
conf t
ip domain-name cisco.com
crypto key generate rsa

username admin secret ccna
line vty 0 15
transport input ssh
login local
exit
ip ssh version 2
exit

Set Clock

Show Clock

show clock

Sets clock to eastern US time

clock timezone EST -5

Revert to Default Timezone

no clock timezone

Basic Hardening (Work Needed)

conf t
! Logout timer
!
line con 0
 exec-timeout 5
line vty 0 4
 exec-timeout 5
 
exit

ip ssh time-out 60
ip ssh authentication-retries 3
end

Backup config over FTP

Using included FTP server

copy running-config startup-config
copy startup-config ftp://192.168.1.10/config.txt

Backup config over console

coming soon

Restore Config

copy ftp://192.168.1.10/config.txt running-config

Nuking (ROMMON, Password Recovery, etc)

Perform a Boot Interupt to Recover a lost or unknown password

WARNING: This operation will delete all current config on the device

  1. Ensure Console Cable is connected at 9600 Baudrate

  2. Backup config if you need

  3. Unplug Power

  4. Wait for a few seconds

  5. Re-insert the power cord to the switch

  6. Within 15 seconds, hold the Mode button until the green flashing light flashes amber and then returns to flashing green. Release the Mode button.

  7. Something like the following should display:

    initialize the flash file system, and finish loading the operating system software#

flash_init
load_helper
boot

  8. Run flash_init

  9. Run copy flash:config.text flash:config.text.old

  10. Run boot

    The device should now boot with no config and grant you access to it.

Interfaces

Interface Selection

Assign and IP address to a port

conf t
int f0/1
ip addr 192.168.10.11 255.255.255.0
end

Assign Static IP to Interface

conf t
int g0/0
ip addr 10.0.0.10 255.255.255.0

Interface Ranges

Assign and IP address to a port

conf t
int f0/1
ip addr 192.168.10.11 255.255.255.0
end

Select Single Range and Assign to a VLAN

conf t
int range f0/1-12
switchport mode access
switch access vlan 10
end

conf t
int range f0/13-24
switchport mode access
switchport access vlan 20
end

Select Multiple Interface Ranges and Move to a VLAN

conf t
int range f0/1-4,g0/1,f0/16-20
switchport mode access
switchport access vlan 10
end

Interface Verification

show ip interface brief

or

show ip int br

Remove IP Addresses

conf t
int f0/1
no ip addr
end

Console Port

Change Console Baudrate

conf t
line con 0
speed 115200
end

conf t
line con 0
speed 9600
end

DHCP

Snippet: Enable Router DHCP Server

This snippet configures a DHCP Server on R1 and will hand out IPs on the 10.0.0.1/24 network. Great for using an FTP Server with.

conf t
ip domain name cisco.com
ip dhcp excluded-address 10.0.0.1
ip dhcp pool test
network 10.0.0.0 255.255.255.0
default-router 10.0.0.1
end

Snippet: Enable Switch DHCP Server

ip dhcp pool test
network 10.0.0.0 255.255.255.0
domain-name cisco.com
default-router 10.0.0.1
dns-server 10.0.0.1
lease 4
ip dhcp snooping
ip dhcp-server 10.0.0.3
interface vlan 1
ip address 10.0.0.3

Create DHCP Pool

Workaround for CCNA labs at Liberty University since we can't change the LAB IP addresses

conf t
ip domain name cisco.com
ip dhcp excluded-address 10.0.0.1
ip dhcp pool managementpool
network 10.0.0.1 255.255.255.0
default-router 10.0.0.1
end

conf t
ip dhcp excluded-address 192.168.10.1
ip dhcp excluded-address 192.168.10.254
ip dhcp pool office-pool-1
network 192.168.10.0 255.255.255.0
default-router 192.168.10.1
dns-server 192.168.5.5
domain-name linux.org
end

DHCP Verification

show running-config | section dhcp
show ip dhcp binding
show ip dhcp server statistics

Disable DHCP

conf t
no service dhcp
end

Re-enabled DHCP

conf t
service dhcp
end

Create VLAN DHCP

Creates a Seperate DHCP Pool for each VLAN

Create VLANS

conf t
vlan 10
name Management
vlan 20
name Sales
vlan 30
name Operations
end

Configure SVI's and IP Address

VLAN IP Address Gateway
10 192.168.10.254 192.168.10.1
20 192.168.20.254 192.168.20.1
30 192.168.30.254 192.168.30.1 
conf t
int vlan 10
ip address 192.168.10.254 255.255.255.0
ip default-gateway 192.168.10.1
no shut

int vlan 20
ip address 192.168.20.254 255.255.255.0
ip default-gateway 192.168.20.1
no shut

int vlan 30
ip address 192.168.30.254 255.255.255.0
ip default-gateway 192.168.30.1
no shut
end

Add interfaces to VLANS, 8 ports per vlan

conf t
int range f0/1-7
switchport mode access
switchport access vlan 10

int range f0/8-15
switchport mode access
switchport access vlan 20

int range f0/16-24
switchport mode access
switchport access vlan 30
end

Create DHCP Pools for each vlan

conf t
ip domain name cisco.com
ip dhcp excluded-address 192.168.10.1
ip dhcp pool vlan10pool
network 192.168.10.0 255.255.255.0
default-router 192.168.10.1
import all


ip dhcp excluded-address 192.168.20.1
ip dhcp pool vlan20pool
network 192.168.20.0 255.255.255.0
default-router 192.168.20.1
import all

ip dhcp excluded-address 192.168.30.1
ip dhcp pool vlan30pool
network 192.168.30.0 255.255.255.0
default-router 192.168.30.1
import all
end

Now when a device plugs into a port f0/4 for instance and performs a DHCP request, it should get an IP like 192.168.10.3 because it is plugged into the ports assigned to VLAN 10

Verify DHCP Pool

show ip dhcp pool

Delete DHCP Pool

conf t
no ip dhcp pool managementpool
end

Intermediate Networking

VLANs

VLAN Creation

conf t
vlan 10
name Faculty
exit

conf t
vlan 20
name Students
exit

Port Assignment

conf t
interface range Fa0/1-12
switchport mode access
switchport access vlan 10
end

conf t interface range Fa0/13-24
switchport mode access
switchport access vlan 20
end

conf t
interface Gi0/1
switchport mode access
switchport access vlan 99
end

IP Assignemnt

conf t
int vlan 99
ip address 10.0.0.1 255.255.255.0
end

Verification

show vlan brief

Voice and Data VLAN

Assuming Data on VLAN 10, Voice on VLAN 20

conf t
int Fa0/4
switchport mode access
switchport access vlan 10
switchport voice vlan 20
end

Management VLAN

conf t
vlan 99
name Management
exit
interface Fa0/24
switchport mode access
switchport access vlan 99
exit
int vlan 99
ip addr 10.0.0.1 255.255.255.0
end

Delete VLANS on file

delete vlan.dat

Delete VLANS in memory

Warning: Make sure you move ports to another vlan or the will be unsable

conf t
no vlan 10
no vlan 20
end

Inter-VLAN Routing

Creates multiple sub-interfaces on a router port to enable inter-vlan routing.

Note: encapsulation dot1q must be called on a sub interface before an IP can be assigned to it.

conf t
interface G0/0/1.10
description Default Gateway for VLAN 10
encapsulation dot1Q 10
ip add 192.168.10.1 255.255.255.0
exit

interface G0/0/1.20
description Default Gateway for VLAN 20
encapsulation dot1Q 20
ip addr 192.168.20.1 255.255.255.0
exit

interface G0/0/1.99
description Default Gateway for VLAN 99
encapsulation dot1Q 99
ip addr 192.168.99.1 255.255.255.0
exit

interface G0/0/1
description Trunk link to S1
no shut
end

Trunks

Create multi-switch vlan trunk

S1

conf t
interface Gi0/1
description Trunk Line to S2 Gi0/1
switchport mode trunk
switchport trunk native vlan 99
switchport trunk allowed vlan 99
end

Note: Remember to set the native vlan (to 99 for instance) on each switch in the trunk so you don't get a native vlan mismatch warning

Trunk Verification

show interface trunk
show interface g0/1 switchport

EtherChannel

Etherchannel protocols LACP and PAgP configure multiple physical interfaces and links to act as one logical one. You can configure up to 8 ports to act as a single link. This increases bandwidth and improves redundancy.

Note: mode active sets the etherchannel group to use the LACP protocol

Configure EtherChannel

Configure etherchannel between two switches connected with two ethernet cables.

conf t
int range f0/1-2
channel-group 1 mode active
exit
int port-channel 1
switchport mode trunk
switchport trunk allowed vlan 1,2,20

Verify EtherChannel

show interfaces trunk
show etherchannel summary

DTP (Dynamic Trunking Protocol)

Configure DTP

conf t
int gi0/1
switchport mode dynamic auto
end

or

conf t
int gi0/1
switchport mode dynamic desirable
end

Disable DTP

Usefull for connecting to devices that don't support Cisco propietary DTP or creating a static trunk

conf t
int gi0/1
switchport mode trunk
switchport nonegotiate
end

Verify DTP

show dtp interface gi0/1

Advanced Networking

OSPFv2

OSPF Router IDs

All Commands
show ip ospf neighbor
show ip ospf database
Enable router OSPF process

Starting Mode: Global, Non-enabled

enable
conf t
router ospf 10
Configure Loopback
enable
conf t
interface Loopback 1
ip addr 1.1.1.1 255.255.255.255
end
Configure OSPF Router ID

replace 1.1.1.1 with desired id

conf t
router ospf 10
router-id 1.1.1.1
end
Modify OSPF router ID

Prompt confirmation with 'y' needed

conf t
router ospf 10
router-id 1.1.1.2
end
clear ip ospf process

Verify

show ip proto | include Router ID

OSPF - Point-to-Point Networks

Network Command Syntax

Router(config-router)# network network-address wildcard-mask area area-id

Configure OSPF With Network Command

The following configures a trianngle of 3 routers connected to each other as an OSPF point to point network.

conf t
router ospf 10
network 10.10.1.0 0.0.0.255 area 0
network 10.10.1.4 0.0.0.3 area 0
network 10.10.1.12 0.0.0.3 area 0
end
Use Entire Gigabit Interfaces
conf t
router ospf 10
network 10.10.1.1 0.0.0.0 area 0
network 10.10.1.5 0.0.0.0 area 0
network 10.10.1.14 0.0.0.0 area 0
end
Configure OSPF with ip ospf

Configure OSPF directly on the interfaces rather with with the network command.

Syntax: Router(config-if)# ip ospf <process-id> area <area-id>

R1(config)# router ospf 10
R1(config-router)# no network 10.10.1.1 0.0.0.0 area 0
R1(config-router)# no network 10.1.1.5 0.0.0.0 area 0
R1(config-router)# no network 10.1.1.14 0.0.0.0 area 0
R1(config-router)# interface GigabitEthernet 0/0/0
R1(config-if)# ip ospf 10 area 0
R1(config-if)# interface GigabitEthernet 0/0/1 
R1(config-if)# ip ospf 10 area 0
R1(config-if)# interface Loopback 0
R1(config-if)# ip ospf 10 area 0
R1(config-if)#
OSPF Passive Interfaces
conf t
router ospf 10
passive-interface loopback 0
end

conf t
router ospf 10
passive-interface Gi0/0/0
end
Find Designated Router and Backup
show ip ospf interface GigabitEthernet 0/0/0
Change OSPF from Broadcast to Point-to-Point
conf t
interface GigabitEthernet 0/0/0
ip ospf network point-to-point
Loopback and P2P Networks

Loobacks can be used to simulate real LAN networks

conf t
interface Loopback 0
ip ospf network point-to-point

show ip route | include 10.10.1

Multiaccess OSPF Networks

Configure OSPF Priority
conf t
int g0/0/1
ip ospf priority 255
end

Where 255 can be values from 0 to 255 with higher numbers making the router to be elected DR.

Modifying Single Area OSPF

Adjusting Reference Bandwidth
Router# router ospf 10
Router(config-router) auto-cost reference bandwidth 1000

Where 1000 is the speed of the link in Mpbs Common Values: 10, 100, 1000

Manually Set OSPF Link Cost
conf t
int g0/0/1
ip ospf cost 25
interface l0
ip ospf cost 15
end
Show OSPF Hello Packet Intervals
show ip ospf int g0/0/1
Set OSPF Hello Packet Intervals
Router(config-if)# ip ospf hello-interval <seconds>

conf t
int g0/0/1
ip ospf hello-interval 30
end

Note: dead-interval automatically gets set as hello-interval * 4

Set OSPF Dead Interval

OSPF Default Routes

Propogate Default Route
conf t
ip route 0.0.0.0 0.0.0.0 loopback 1
router ospf 10
default-information originate
Verify Propogated Default Route
show ip route | begin Gateway

Verify Single-Area OSPF

Verify OSPF Neighbors
show ip ospf neighbor
Verify OSPF Protocols
show ip protocols
Verify OSPF Process Info
show ip ospf
Verify OSPF Interface Setting
show ip ospf int g0/0/1
show ip ospf int brief

Where g0/0/1 is the interface you was to see OSPF information on.

conf t
int g0/0/1
ip ospf dead-interval 100
end

How To's

FTP Server Usage

  1. Clone the repo:

    git clone https://github.com/grplyler/cisco-utils

  2. Install python requirements (for ftp server):

    pip install -r requirements.txt

  3. Run python ftp_server.py

    python3 ftp_server.py

  4. Pull a script onto a network device (WARNING: Backup to avoid any losses)

    Switch#> copy ftp://192.168.1.10/sw_base.txt running-config

    Replace 192.168.1.10 with the IP of the computer connected to the switch or router.

Install Packet Tracer on Fedora Workstation

(Credit for this howto goes to philpinch from the Fedora Forums)

1. Log into the Fedora GNOME Desktop

Remove old version of PacketTracer (if necessary):

rm -rf /opt/pt
rm -rf /usr/share/applications/cisco-pt7.desktop
rm -rf /usr/share/applications/cisco-ptsa7.desktop
rm -rf /usr/share/icons/hicolor/48x48/apps/pt7.png

2. Download from the netacad web site the PacketTracer_730_amd64.deb package.

Open a terminal :

mkdir -p tmp/pt730

copy the PacketTracer_730_amd64.deb package to tmp/pt730

4. We’re going to extract the deb file in this folder:

cd tmp/pt730
ar -xv PacketTracer_730_amd64.deb
mkdir control
tar -C control -Jxf control.tar.xz
mkdir data
tar -C data -Jxf data.tar.xz

5. Copy PacketTracer files to install it:

cd data
cp -r usr /
cp -r opt /

6. Configure Gnome Environment:

sudo xdg-desktop-menu install /usr/share/applications/cisco-pt7.desktop
sudo xdg-desktop-menu install /usr/share/applications/cisco-ptsa7.desktop
sudo update-mime-database /usr/share/mime
sudo gtk-update-icon-cache --force --ignore-theme-index /usr/share/icons/gnome
sudo xdg-mime default cisco-ptsa7.desktop x-scheme-handler/pttp
ln -sf /opt/pt/packettracer /usr/local/bin/packettracer

Console Access with minicom on Linux

under construction

Configure Serial Port with stty on Linux

Set the default configuration with stty to cisco console default, 9600 bps, 8N1, no flow control:

stty -F /dev/ttyUSB0 9600 litout -crtscts

or:

stty -F /dev/ttyUSB0 cs8 -parenb -cstopb -echo raw speed 9600

 # What the arguments mean:
 #   cs8:     8 data bits
 #   -parenb: No parity (because of the '-')
 #   -cstopb: 1 stop bit (because of the '-')
 #   -echo: Without this option, Linux will sometimes automatically send back
 #          any received characters, even if you are just reading from the serial
 #          port with a command like 'cat'. Some terminals will print codes
 #          like "^B" when receiving back a character like ASCII ETX (hex 03).

Console Access with Screen on Linux

For this you will need a USB console cable. These can be picked up on amazon for about $9-$12.

  1. Connect your the USB console cable from the computers usb port to the cisco RJ-45 console port.

  2. Install the screen program if you dont already have it.

apt install screen
  1. Find the USB device.

If its the first USB serial device you plugged in, it should be /dev/ttyUSB0. The second one should be /dev/ttyUSB1, etc.

You can verify with with ls /dev | grep USB

  1. Run screen

You will need root access.

screen /dev/ttyUSB0

Running with a specific baudrate.

screen /dev/ttyUSB0 9600
screen /dev/ttyUSB0 115200

To exit screen, hit Ctrl-a, Ctrl-d

If you have trouble with the connection, e.g. it lags or is funky, cisco serial connections require the following settings by default:

  • 9600 baud
  • 8 data bits
  • no parity
  • 1 stop bit
  • no flow control

To do that exactly with screen:

screen /dev/ttyS0 9600,cs8,-parenb,-cstopb,-hupcl
screen /dev/ttyS0 19200,cs8,-parenb,-cstopb,-hupcl
screen /dev/ttyS0 115200,cs8,-parenb,-cstopb,-hupcl

With odd parity:

screen /dev/ttyS0 9600,cs8,parenb,parodd,-cstopb,-hupcl

With even parity:

screen /dev/ttyS0 9600,cs8,parenb,-parodd,-cstopb,-hupcl

See more details at http://www.noah.org/wiki/Screen_notes

Linux File Transfer Over Console (minicom / xmodem)

Howto comming soon!

Windows File Transfer Over Console ( HyperTerminal / xmodem)

Howto comming soon!

Tools

Subnetting/Calcuation

ipcalc (*nix)

Debian/Ubuntu

apt install ipcalc

Fedora

dnf install ipcalc

yum install ipcalc

sipcalc (*nix)

Debian/Ubuntu

apt install sipcalc

or replace apt with your package manager

whatmask (*nix)

Example Usage

$ whatmask 10.0.1.12/30

------------------------------------------------
           TCP/IP NETWORK INFORMATION
------------------------------------------------
IP Entered = ..................: 10.0.1.12
CIDR = ........................: /30
Netmask = .....................: 255.255.255.252
Netmask (hex) = ...............: 0xfffffffc
Wildcard Bits = ...............: 0.0.0.3
------------------------------------------------
Network Address = .............: 10.0.1.12
Broadcast Address = ...........: 10.0.1.15
Usable IP Addresses = .........: 2
First Usable IP Address = .....: 10.0.1.13
Last Usable IP Address = ......: 10.0.1.14

Install

Debian/Ubuntu

apt install whatmask

or replace apt with your package manager

About

A Cisco Cheatsheet: Commands and Snippets for bootstrapping, boilerplate, configuration, and hardening of Cisco routers and switches.

Topics

cisco scripts cheatsheet cheat-sheet ccna cisco-packet-tracer cisco-ios vlan-creation ccnav7 cisco-cheatsheet

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