how to configured three routers cisco 1841 NAT configuration with steps 2026
Configure Three Cisco 1841 Integrated Services Router Routers with NAT (2026)
This example shows:
3 Cisco 1841 routers
Static routing
NAT configuration
LAN to WAN communication
Internet simulation
Network Topology
PC1 ---- R1 ---- R2 ---- R3 ---- Server/Internet
LAN1 WAN1 WAN2 PUBLIC
IP Addressing Table
| Device | Interface | IP Address | Subnet Mask |
|---|---|---|---|
| R1 | Fa0/0 | 192.168.1.1 | 255.255.255.0 |
| R1 | S0/0/0 | 10.0.12.1 | 255.255.255.252 |
| R2 | S0/0/0 | 10.0.12.2 | 255.255.255.252 |
| R2 | S0/0/1 | 10.0.23.1 | 255.255.255.252 |
| R3 | S0/0/1 | 10.0.23.2 | 255.255.255.252 |
| R3 | Fa0/0 | 200.1.1.1 | 255.255.255.0 |
| PC1 | NIC | 192.168.1.10 | 255.255.255.0 |
| Server | NIC | 200.1.1.10 | 255.255.255.0 |
Step 1: Connect Routers
Use:
Console cable for initial setup
Serial DCE/DTE cable between routers
Ethernet cable to PCs
Example:
R1 S0/0/0 <----> R2 S0/0/0
R2 S0/0/1 <----> R3 S0/0/1
Step 2: Configure Router R1
enable
configure terminal
hostname R1
interface fastethernet0/0
ip address 192.168.1.1 255.255.255.0
no shutdown
interface serial0/0/0
ip address 10.0.12.1 255.255.255.252
clock rate 64000
no shutdown
exit
ip route 0.0.0.0 0.0.0.0 10.0.12.2
Step 3: Configure Router R2
enable
configure terminal
hostname R2
interface serial0/0/0
ip address 10.0.12.2 255.255.255.252
no shutdown
interface serial0/0/1
ip address 10.0.23.1 255.255.255.252
clock rate 64000
no shutdown
exit
ip route 192.168.1.0 255.255.255.0 10.0.12.1
ip route 200.1.1.0 255.255.255.0 10.0.23.2
Step 4: Configure Router R3
enable
configure terminal
hostname R3
interface serial0/0/1
ip address 10.0.23.2 255.255.255.252
no shutdown
interface fastethernet0/0
ip address 200.1.1.1 255.255.255.0
no shutdown
exit
ip route 192.168.1.0 255.255.255.0 10.0.23.1
Step 5: Configure NAT on R3
Inside network:
192.168.1.0/24
Outside network:
200.1.1.0/24
Configure NAT:
configure terminal
access-list 1 permit 192.168.1.0 0.0.0.255
Configure NAT Inside and Outside Interfaces
interface serial0/0/1
ip nat inside
interface fastethernet0/0
ip nat outside
Enable PAT (NAT Overload)
ip nat inside source list 1 interface fastethernet0/0 overload
Step 6: Configure PC
PC1
IP Address : 192.168.1.10
Subnet Mask: 255.255.255.0
Gateway : 192.168.1.1
Server
IP Address : 200.1.1.10
Subnet Mask: 255.255.255.0
Gateway : 200.1.1.1
Step 7: Save Configuration
On all routers:
copy running-config startup-config
Step 8: Verify Configuration
Check Interfaces
show ip interface brief
Check Routing Table
show ip route
Check NAT Translations
show ip nat translations
Check NAT Statistics
show ip nat statistics
Step 9: Test Connectivity
From PC1:
ping 200.1.1.10
Successful replies confirm:
Routing works
NAT works
Three-router communication works
NAT Configuration Diagram
Important NAT Commands
| Command | Purpose |
|---|---|
ip nat inside | Marks inside interface |
ip nat outside | Marks outside interface |
ip nat inside source list | Enables NAT |
overload | Enables PAT |
show ip nat translations | Shows NAT table |
Troubleshooting
If ping fails
Check:
show controllers serial 0/0/0
Verify DCE cable and clock rate.
If NAT not working
Check:
show running-config
Verify:
ACL is correct
Inside/outside interfaces are correct
Routes are configured
Practice in Simulator
You can practice using: