Lista-4

by Jerry Sky

The original task (in polish)

»English« > 1. W symulatorze GNS3 skonfiguruj wirtualną sieć o podanej topologii, tak aby: > simulation > 1. Wirtualna sieć była połączona z zewnętrzną („fizyczną”) siecią Cloud. > 2. Ruter R5 uzyskiwał dynamiczny adres IP z sieci Cloud. > 3. Pozostałe urządzenia posiadały statyczne adresy w swoich sieciach. > 4. Możliwe było wysyłanie komunikatów ping pomiędzy dowolna parą urządzeń sieci wirtualnej. > 5. Możliwe było wysyłanie komunikatów ping z dowolnego urządzenia w sieci wirtualnej na zewnętrzny adres, np. google.com. > 2. Ustaw przechwytywanie komunikatów w sieciach: 192.168.0.0, 192.168.2.0, 192.168.3.0. > 3. Przeanalizuj przechwycone komunikaty dla zapytania wysłanego z komputera PC2: ping google.com.

Translated task

  1. In GNS3 simulation program create a virtual network with a given topology such that: simulation
    1. the virtual network is connected with the outside „physical” network represented by device named Cloud.
    2. R5 has a dynamic IP address given by Cloud
    3. other devices have their static IP address inside their local networks
    4. all devices are able to communicate with each other via ping
    5. all devices are able to communicate with the outside world e.g. google.com
  2. Setup packet capture on networks 192.168.0.0., 192.168.2.0, 192.168.3.0.
  3. Analyse captured packets sent and received due to executing ping google.com in the terminal of PC2.

Useful commands

  1. After executing conf t:
    1. After executing int X, where X is a network interface e.g. f0/0:
      1. no ip address deletes current settings for chosen network interface
  2. do execute a command like outside conf t
  3. sh show (show):
    1. ip route currently active internet interfaces
    2. access-list views the list of IPs with their access mode

Setting up

Important: in order for this simulation to run an image of the CISCO c3725 router has to bo installed into GNS3. Download it from here or just run attached bash script with wget in it.

Obviously, on every computer the configuration of the Cloud will be different thus the gateway and the subnet will be different (hence they need to be reconfigured a little in order to work on your machine).
However, the inside of this network of smaller networks should work out of the box. If it’s not below are setup commands that have to be run consecutively in each device’s terminal to be setup properly.

Testing

After the setup you can test the simulated network. Open selected device’s terminal and use ping to test the connection to another device in the network. DNS is set to either 8.8.8.8 (Google) or 1.1.1.1 so pinging outside web should also not be a problem.

Other caveats

Devices marked as PC-X where X ∈{1,2,3}\in \{1,2,3\} are not actual GNS3’s VPCSs. They are the CISCO c3725 routers with ip routing turned off so they act like a VPCS.
This is sufficient for testing purposes of this simulation.
(normal GNS3’s VPCSs are genuinely broken)

Devices’ configs

R5 (last router before Cloud)

conf t
int f0/0
ip address dhcp
ip nat outside
no shut
end

conf t
ip domain-lookup
ip name-server 8.8.8.8
end

conf t
int f0/1
ip add 192.168.3.3 255.255.255.0
ip nat inside
no shut
end

conf t
router rip
version 2
no auto-summary
network 192.168.42.0
network 192.168.3.0
default-information originate
end

conf t
access-list 10 permit 192.168.1.0 0.0.254.255
access-list 10 permit 192.168.2.0 0.0.253.255
access-list 10 permit 192.168.3.0 0.0.252.255
access-list 10 permit 192.168.4.0 0.0.251.255

ip nat inside source list 10 interface f0/0 overload
end

R6

conf t
int f0/0
no shut
ip add 192.168.3.1 255.255.255.0
end

conf t
ip domain-lookup source-interface f0/0
ip name-server 8.8.8.8
end

conf t
int f1/0
no shut
ip add 192.168.1.1 255.255.255.0
end

conf t
int f0/1
no shut
ip add 192.168.4.1 255.255.255.0
end

conf t
router rip
version 2
no auto-summary
network 192.168.1.0
network 192.168.4.0
network 192.168.3.0
end

R2

conf t
int f0/1
ip add 192.168.2.1 255.255.255.0
no shut
int f0/0
ip add 192.168.4.2 255.255.255.0
no shut
end

conf t
router rip
version 2
no auto-summary
network 192.168.2.0
network 192.168.4.0
end

conf t
ip domain-lookup
ip name-server 8.8.8.8
end

R3

conf t
int f0/0
ip add 192.168.2.3 255.255.255.0
no shut
end

conf t
router rip
version 2
no auto-summary
network 192.168.2.0
end

conf t
ip domain-lookup
ip name-server 192.168.42.129
end
write memory

PC-1

conf t
no ip routing
int f0/0
ip add 192.168.1.2 255.255.255.0
no shut
exit
ip default-gateway 192.168.1.1
ip domain-lookup
ip name-server 8.8.8.8
end
write memory

PC-2

conf t
no ip routing
int f0/0
ip add 192.168.2.4 255.255.255.0
no shut
exit
ip default-gateway 192.168.2.1
ip domain-lookup
ip name-server 8.8.8.8
end
write memory

PC-3

conf t
no ip routing
int f0/0
ip add 192.168.2.5 255.255.255.0
no shut
exit
ip default-gateway 192.168.2.1
ip domain-lookup
ip name-server 8.8.8.8
end
write memory