Getting Internet in GNS3 using a Cisco Router

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Topology

Your topology consists of:

• R1 (Router)

  • f0/0 (Connected to NAT1) - Acts as a DHCP client (gets IP from NAT)

  • f1/0 (Connected to PC1) - 192.168.0.1/24

• PC1

  • e0 (Connected to R1's f1/0) - 192.168.0.100/24

• NAT1 (Internet Simulation)

Step 1: Configure the NAT Interface (f0/0)

• Enter the router's configuration mode:

R1#configure terminal

• Configure f0/0 to get an IP via DHCP:

R1(config)#interface fastEthernet 0/0
R1(config-if)#ip address dhcp
R1(config-if)#no shutdown
R1(config-if)#

Step 2: Configure LAN Interface (f1/0)

• Assign an IP to f1/0 and enable it:

R1(config)#interface fastEthernet 1/0
R1(config-if)#ip address 192.168.0.1 255.255.255.0
R1(config-if)#no shutdown
R1(config-if)#

Step 3: Configure NAT for Internet Access

• Enable NAT on f0/0 (outside) and f1/0 (inside):

R1(config)#interface fastEthernet 0/0
R1(config-if)#ip nat outside
R1(config-if)#exit
R1(config)#interface fastEthernet 1/0
R1(config-if)#ip nat inside
R1(config-if)#exit

• Create an ACL to allow local network traffic:

R1(config)#access-list 1 permit 192.168.0.0 0.0.0.255

• Configure NAT overload:

R1(config)#ip nat inside source list 1 interface FastEthernet0/0 overload

• Verify NAT:

R1#show ip nat translations

Step 4: Configure and Test PC1

• Assign an IP and default gateway to PC1:

PC1> ip 192.168.0.100/24 192.168.0.1
Checking for duplicate address...
PC1 : 192.168.0.100 255.255.255.0 gateway 192.168.0.1

PC1> show ip

NAME        : PC1[1]
IP/MASK     : 192.168.0.100/24
GATEWAY     : 192.168.0.1
DNS         :
MAC         : 00:50:79:66:68:00
LPORT       : 20008
RHOST:PORT  : 127.0.0.1:20009
MTU         : 1500

PC1> save
Saving startup configuration to startup.vpc
.  done

PC1>

• Test connectivity to R1:

PC1> ping 192.168.0.1

84 bytes from 192.168.0.1 icmp_seq=1 ttl=255 time=70.532 ms
84 bytes from 192.168.0.1 icmp_seq=2 ttl=255 time=16.052 ms
^C
PC1>

• Test internet connectivity:

PC1> ping 8.8.8.8

84 bytes from 8.8.8.8 icmp_seq=1 ttl=126 time=99.708 ms
84 bytes from 8.8.8.8 icmp_seq=2 ttl=126 time=81.077 ms
^C
PC1>

Step 5: Configure and Verify Routing

• Ensure R1 has a default route to the internet:

R1(config)#ip route 0.0.0.0 0.0.0.0 fastEthernet 0/0

Step 6: Test and Troubleshoot

• Check if NAT is translating:

R1#show ip nat statistics
Total active translations: 0 (0 static, 0 dynamic; 0 extended)
Peak translations: 2, occurred 00:02:59 ago
Outside interfaces:
  FastEthernet0/0
Inside interfaces:
  FastEthernet1/0
Hits: 4  Misses: 0
CEF Translated packets: 4, CEF Punted packets: 0
Expired translations: 2
Dynamic mappings:
-- Inside Source
[Id: 1] access-list 1 interface FastEthernet0/0 refcount 0

Total doors: 0
Appl doors: 0
Normal doors: 0
Queued Packets: 0
R1#

Keywords

GNS3, Cisco Router, Internet Access, NAT Configuration, DHCP Client, FastEthernet, IP Address, Default Gateway, Routing, ACL, NAT Overload, Ping Test, Network Topology, Packet Forwarding, Troubleshooting, Static Route, Dynamic IP, PC Connectivity, NAT Translations, Show Commands, سیسکو