how to configure leased line two routers with serial cable with commands 2025

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Leased Line Configuration Between Two Routers Using Serial Cable (2025)

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1. What Is a Leased Line?

how to configure leased line two routers with serial cable with commands 2025Aleased line

is a dedicated, point-to-point communication link permanently reserved between two locations. Unlike broadband or shared networks, a leased line:

• Is always ON
• Provides fixed bandwidth
• Has low latency
• Is highly secure
• Uses point-to-point protocols

In router labs, leased lines are simulated using serial interfaces (DCE/DTE).

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2. Real-World vs Lab Leased Line

Real World	Lab Simulation
ISP fiber / copper	Serial cable
CSU/DSU	DCE interface
Monthly rental	No cost
SLA guaranteed	Manual clock rate

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3. Network Topology

   Router1 (R1) -------- Serial Cable -------- Router2 (R2)
         S0/0/0                         S0/0/0

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4. Requirements

Hardware

• 2 Routers (Cisco 1841 / 2811 / ISR / Packet Tracer routers)
• 1 Serial DCE/DTE cable

Software

• Cisco IOS
• Packet Tracer / GNS3 / Real devices

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5. IP Addressing Plan

Device	Interface	IP Address	Subnet Mask
R1	Serial0/0/0	10.10.10.1	255.255.255.252
R2	Serial0/0/0	10.10.10.2	255.255.255.252

/30 subnet is best for leased lines (only 2 usable IPs).

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6. DCE vs DTE Explanation

Term	Meaning
DCE	Provides clock rate
DTE	Receives clock
Clock Rate	Mandatory on DCE side

Check DCE side

Router# show controllers serial 0/0/0

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7. Router 1 Configuration (R1)

Step 1: Enter Privileged Mode

Router> enable

Step 2: Enter Global Configuration

Router# configure terminal

Step 3: Set Hostname

Router(config)# hostname R1

Step 4: Configure Serial Interface

R1(config)# interface serial 0/0/0

Step 5: Assign IP Address

R1(config-if)# ip address 10.10.10.1 255.255.255.252

Step 6: Set Clock Rate (Only if DCE)

R1(config-if)# clock rate 64000

Step 7: Set Encapsulation (PPP recommended)

R1(config-if)# encapsulation ppp

Step 8: Enable Interface

R1(config-if)# no shutdown

Step 9: Exit

R1(config-if)# exit

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8. Router 2 Configuration (R2)

Step 1: Enter Privileged Mode

Router> enable

Step 2: Enter Global Configuration

Router# configure terminal

Step 3: Set Hostname

Router(config)# hostname R2

Step 4: Configure Serial Interface

R2(config)# interface serial 0/0/0

Step 5: Assign IP Address

R2(config-if)# ip address 10.10.10.2 255.255.255.252

Step 6: Set Encapsulation

R2(config-if)# encapsulation ppp

Step 7: Enable Interface

R2(config-if)# no shutdown

Step 8: Exit

R2(config-if)# exit

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9. Verify Interface Status

Check Interface

R1# show ip interface brief
R2# show ip interface brief

Expected Output:

Serial0/0/0    10.10.10.1    up   up
Serial0/0/0    10.10.10.2    up   up

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10. Test Connectivity

Ping Test

R1# ping 10.10.10.2
R2# ping 10.10.10.1

✔ Successful replies confirm leased line is working.

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11. Optional: Enable Authentication (PPP CHAP)

Configure Username

R1(config)# username R2 password cisco
R2(config)# username R1 password cisco

Enable CHAP

R1(config)# interface serial 0/0/0
R1(config-if)# ppp authentication chap

R2(config)# interface serial 0/0/0
R2(config-if)# ppp authentication chap

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12. Optional: Static Routing (If LANs Are Connected)

Example LANs

how to configure leased line two routers with serial cable with commands 2025

• R1 LAN: 192.168.1.0/24
• R2 LAN: 192.168.2.0/24

Static Routes

R1(config)# ip route 192.168.2.0 255.255.255.0 10.10.10.2
R2(config)# ip route 192.168.1.0 255.255.255.0 10.10.10.1

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13. Common Troubleshooting Commands

show ip interface brief
show interfaces serial 0/0/0
show controllers serial 0/0/0
show running-config
debug ppp negotiation

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14. Common Issues & Fixes

Problem	Solution
Interface down	no shutdown
Line protocol down	Check encapsulation
No ping	Check IP & subnet
Clock error	Configure clock rate
Auth failure	Match CHAP username

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15. Real-World ISP Leased Line Notes (2025)

• Uses PPP or HDLC
• Clock rate managed by ISP
• SLA includes uptime (99.5%+)
• Static IPs provided
• Used by banks, data centers, enterprises

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16. Interview Questions

1. Why use /30 subnet for leased lines?
2. Difference between DCE and DTE?
3. PPP vs HDLC?
4. What is clock rate?
5. How to troubleshoot serial links?

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17. Conclusion

A leased line using serial cable provides:

• Dedicated connectivity
• Stable performance
• Secure communication
• Enterprise-grade networking

This configuration is still relevant in 2025 for:

• CCNA/CCNP labs
• Networking training
• Interview preparation
• Packet Tracer simulations

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If you want, I can also provide:
✔ Packet Tracer file
✔ Diagram image
✔ Three-router leased line
✔ Leased line with ACL
✔ Leased line with DHCP

Leased line (point to point connection dedicated bandwidth) more expensive ”1.44mb t1 line”

Use for authentication over leased line by using CHAP (challenge hand shake authentication protocol) & PAP (password authentication Protocol)

More secure is CHAP.

1. Configure ip add & routing
2. Ping and check (will be able to ping)
3. Change hostname r0 & r1 on both router
4. On r0

r0(config)#username r1 password cisco

r0(config)#int s1/0

r0(config-if)#encapsulation ppp

r0(config-if)#ppp authentication chap

5. Ping and check (cant ping)
6. On r1

r1(config)#username r0 password cisco

r1(config)#int s1/0

r1(config-if)#encapsulation ppp

r1(config-if)#ppp authentication chap

7. Ping and check (will be able to ping)
8. In the place of chap use pap and check(if you are not getting out put with pap use “pap chap”)