Complete MPLS Traffic Engineering Configuration Guide | Cisco MPLS TE with RSVP & Explicit Tunnels

Complete MPLS Traffic Engineering Configuration Guide Part 2

Welcome to Part 2 of the MPLS Service Provider series.

In this tutorial we will configure:

• MPLS Traffic Engineering (MPLS TE)
• RSVP Bandwidth Reservation
• Explicit Path Tunnels
• Traffic Engineered LSPs
• Autoroute Announce
• Bandwidth Constraints
• Tunnel Priorities

🎯 What You Will Learn

• What MPLS Traffic Engineering is
• Why MPLS TE is important
• How RSVP reserves bandwidth
• How explicit paths work
• How TE tunnels override shortest path routing
• How tunnel priorities affect traffic flow
• How bandwidth constraints influence path selection
• How MPLS TE improves traffic optimization

Table of Contents

• 1. MPLS Traffic Engineering Introduction
• 2. Enable MPLS Traffic Engineering
• 3. Enable MPLS TE on Interfaces
• 4. Configure RSVP Bandwidth Reservation
• 5. Configure MPLS TE Tunnel R1 → R4
• 6. Configure MPLS TE Tunnel R2 → R1
• 7. Configure MPLS TE Tunnel R4 → R1
• 8. Configure MPLS TE Tunnel R1 → R3
• 9. Verification and Troubleshooting
• 10. MPLS TE Mathematics
• 11. Related Articles

1. MPLS Traffic Engineering Introduction

Traditional routing protocols choose paths based primarily on shortest path metrics.

This creates several problems:

• Uneven bandwidth utilization
• Congested links
• Underutilized backup paths
• Poor traffic optimization

MPLS Traffic Engineering solves these problems by allowing administrators to manually control packet forwarding paths.

What is MPLS TE?

MPLS TE creates Label Switched Paths (LSPs) with:

• Explicit routing
• Bandwidth reservation
• Priority control
• Path optimization

Traditional Routing Formula

$$ Best\\ Path = Lowest\\ Cost $$

MPLS TE Formula

$$ Best\\ Path = Administrator\\ Defined\\ Path $$

How MPLS TE Works

MPLS TE uses:

• OSPF with TE extensions
• RSVP signaling
• Explicit path configuration
• Constraint-based routing

2. Task 1 - Enable MPLS Traffic Engineering

First we globally enable MPLS Traffic Engineering on all routers.

OSPF must also advertise TE information.

Why OSPF TE Extensions?

Routers must exchange:

• Available bandwidth
• Link attributes
• Tunnel constraints
• Administrative groups

TE Database Formula

$$ TED = OSPF + TE\\ Extensions $$

R1 MPLS TE Configuration

Code Example

mpls traffic-eng tunnels

R1

mpls traffic-eng tunnels
!

router ospf 1
 mpls traffic-eng router-id Loopback0
 mpls traffic-eng area 0

Detailed Explanation

mpls traffic-eng tunnels

Globally enables MPLS TE tunnel support.

mpls traffic-eng router-id Loopback0

Uses Loopback0 as stable TE router identifier.

mpls traffic-eng area 0

Enables OSPF TE extensions in Area 0.

R2 MPLS TE Configuration

R2

mpls traffic-eng tunnels
!

router ospf 1
 mpls traffic-eng router-id Loopback0
 mpls traffic-eng area 0

R3 MPLS TE Configuration

R3

mpls traffic-eng tunnels
!

router ospf 1
 mpls traffic-eng router-id Loopback0
 mpls traffic-eng area 0

R4 MPLS TE Configuration

R4

mpls traffic-eng tunnels
!

router ospf 1
 mpls traffic-eng router-id Loopback0
 mpls traffic-eng area 0

3. Task 2 - Enable MPLS TE on Interfaces

Now enable TE support on provider interfaces.

Why Enable TE on Interfaces?

• Allows RSVP signaling
• Enables bandwidth reservations
• Supports TE tunnel traversal

R1 Interface TE Configuration

R1

interface E0/0
 mpls traffic-eng tunnels
!

interface E0/1
 mpls traffic-eng tunnels
!

interface E0/2
 mpls traffic-eng tunnels

R2 Interface TE Configuration

R2

interface E0/0
 mpls traffic-eng tunnels
!

interface E0/1
 mpls traffic-eng tunnels
!

interface E0/2
 mpls traffic-eng tunnels

R3 Interface TE Configuration

R3

interface E0/0
 mpls traffic-eng tunnels
!

interface E0/1
 mpls traffic-eng tunnels
!

interface E0/2
 mpls traffic-eng tunnels

R4 Interface TE Configuration

R4

interface E0/0
 mpls traffic-eng tunnels
!

interface E0/1
 mpls traffic-eng tunnels
!

interface E0/2
 mpls traffic-eng tunnels

Traffic Engineering Interface Formula

$$ TE\\ Enabled\\ Interface = RSVP + Tunnel\\ Traversal $$

4. Task 3 - Configure RSVP Bandwidth Reservation

RSVP reserves bandwidth for MPLS TE tunnels.

What is RSVP?

RSVP stands for:

Resource Reservation Protocol

It reserves bandwidth along the tunnel path.

Bandwidth Allocation

Interface	Reserved Bandwidth
E0/0	512 kbps
E0/1	512 kbps
E0/2	192 kbps

RSVP Reservation Formula

$$ Available\\ BW = Total\\ BW - Reserved\\ BW $$

R1 RSVP Configuration

R1

interface E0/0
 ip rsvp bandwidth 512
!

interface E0/1
 ip rsvp bandwidth 512
!

interface E0/2
 ip rsvp bandwidth 192

R2 RSVP Configuration

R2

interface E0/0
 ip rsvp bandwidth 512
!

interface E0/1
 ip rsvp bandwidth 512
!

interface E0/2
 ip rsvp bandwidth 192

R3 RSVP Configuration

R3

interface E0/0
 ip rsvp bandwidth 512
!

interface E0/1
 ip rsvp bandwidth 512
!

interface E0/2
 ip rsvp bandwidth 192

R4 RSVP Configuration

R4

interface E0/0
 ip rsvp bandwidth 512
!

interface E0/1
 ip rsvp bandwidth 512
!

interface E0/2
 ip rsvp bandwidth 192

5. Task 4 - Configure Tunnel R1 → R2 → R4

This tunnel forces traffic toward:

$$ 4.4.4.4 $$

through:

$$ R1 \rightarrow R2 \rightarrow R4 $$

Why Explicit Paths?

Explicit paths allow administrators to override shortest path routing.

Explicit Path Formula

$$ Traffic\\ Path = Administrator\\ Defined $$

R1

ip explicit-path name R1-R4 enable
 next-address 2.2.2.2
 next-address 4.4.4.4
!

interface Tunnel14
 ip unnumbered Loopback0
 tunnel destination 4.4.4.4
 tunnel mode mpls traffic-eng

 tunnel mpls traffic-eng autoroute announce
 tunnel mpls traffic-eng priority 4 4
 tunnel mpls traffic-eng bandwidth 128

 tunnel mpls traffic-eng path-option 1 explicit name R1-R4

Tunnel Explanation

autoroute announce

Injects tunnel into routing table.

priority 4 4

Setup and hold priorities.

bandwidth 128

Requests RSVP reservation of 128 kbps.

6. Task 5 - Configure Tunnel R2 → R1

R2

ip explicit-path name R2-R1 enable
 next-address 1.1.1.1
!

interface Tunnel21
 ip unnumbered Loopback0

 tunnel destination 1.1.1.1
 tunnel mode mpls traffic-eng

 tunnel mpls traffic-eng bandwidth 400
 tunnel mpls traffic-eng path-option 1 explicit name R2-R1

 tunnel mpls traffic-eng priority 3 3
 tunnel mpls traffic-eng autoroute announce

Bandwidth Constraint Formula

$$ Requested\\ BW \le Available\\ BW $$

7. Task 6 - Configure Tunnel R4 → R3 → R1

R4

ip explicit-path name R4-R1 enable
 next-address 3.3.3.3
 next-address 1.1.1.1
!

interface Tunnel41
 ip unnumbered Loopback0

 tunnel destination 1.1.1.1
 tunnel mode mpls traffic-eng

 tunnel mpls traffic-eng bandwidth 128
 tunnel mpls traffic-eng path-option 1 explicit name R4-R1

 tunnel mpls traffic-eng priority 3 3
 tunnel mpls traffic-eng autoroute announce

8. Task 7 - Configure High Priority Tunnel R1 → R2 → R3

This tunnel has higher priority:

$$ Priority = 2 $$

Higher priority tunnels can preempt lower priority tunnels.

Tunnel Priority Formula

$$ Lower\\ Number = Higher\\ Priority $$

R1

ip explicit-path name R1-R3 enable
 next-address 2.2.2.2
 next-address 3.3.3.3
!

interface Tunnel13
 ip unnumbered Loopback0

 tunnel destination 3.3.3.3
 tunnel mode mpls traffic-eng

 tunnel mpls traffic-eng bandwidth 400
 tunnel mpls traffic-eng path-option 1 explicit name R1-R3

 tunnel mpls traffic-eng priority 2 2
 tunnel mpls traffic-eng autoroute announce

9. Verification and Troubleshooting

Verify TE Tunnels

show mpls traffic-eng tunnels

Sample Output

Tunnel14:
 Admin: up
 Oper: up
 Path: explicit
 Bandwidth: 128

Verify RSVP Reservations

show ip rsvp reservation

Verify TE Database

show ip ospf mpls traffic-eng

Verify Routing Table

show ip route

Sample Routing Output

R1#show ip route

4.4.4.4/32 via Tunnel14

10. MPLS TE Mathematics

Bandwidth Reservation Formula

$$ Total\\ Reserved = \sum Tunnel\\ Bandwidth $$

RSVP Availability Formula

$$ Free\\ BW = Link\\ BW - Reserved\\ BW $$

Traffic Engineering Formula

$$ Optimal\\ Utilization = Controlled\\ Path\\ Selection $$

Tunnel Preemption Formula

$$ Higher\\ Priority > Lower\\ Priority $$

TE Path Formula

$$ LSP = Explicit\\ Path + RSVP $$

Troubleshooting MPLS TE

Problem	Cause	Solution
Tunnel Down	No RSVP	Enable RSVP bandwidth
No TE Path	TE disabled	Enable TE on interfaces
Bandwidth Failure	Insufficient reservation	Reduce bandwidth request
No Autoroute	Missing autoroute announce	Enable autoroute
No Explicit Path	Incorrect next-address	Verify path addresses

Useful Verification Commands

show mpls traffic-eng tunnels
show ip rsvp reservation
show mpls forwarding-table
show ip route
show ip ospf mpls traffic-eng
show interfaces tunnel

💡 Key Takeaways

• MPLS TE overrides shortest path routing
• RSVP reserves bandwidth for tunnels
• Explicit paths control traffic flow
• Autoroute announce injects TE tunnels into routing
• Lower priority numbers mean higher priority
• TE improves bandwidth utilization
• OSPF advertises TE information
• MPLS TE creates engineered LSPs

11. Related Articles

• Part 1 - Complete MPLS Core Configuration Guide
• Complete MPLS Dynamic Traffic Engineering Configuration Guide | Cisco MPLS TE Lab Part 3

Final Conclusion

This MPLS Traffic Engineering Part 2 tutorial demonstrated how to optimize MPLS forwarding paths using:

• RSVP
• Explicit TE tunnels
• Bandwidth reservation
• Tunnel priorities
• Autoroute announce
• Constraint-based routing

MPLS TE is widely used in enterprise and service provider environments to:

• Prevent congestion
• Optimize WAN utilization
• Guarantee bandwidth
• Improve redundancy
• Provide deterministic forwarding