Complete MPLS Traffic Engineering Configuration Guide
MPLS Traffic Engineering is one of the most important technologies used in modern service provider and enterprise WAN environments.
This guide explains:
- OSPF Configuration
- MPLS LDP
- MPLS Traffic Engineering
- RSVP Bandwidth Reservation
- MPLS TE Tunnels
- Explicit Paths
- Fast Reroute
- Backup Tunnels
- Link Protection
- Bandwidth Engineering
🎯 Learning Objectives
- Understand MPLS TE Architecture
- Learn OSPF Traffic Engineering Extensions
- Understand RSVP Reservation
- Configure MPLS TE Tunnels
- Build Explicit Path Tunnels
- Implement Fast Reroute
- Protect MPLS Core Links
- Understand MPLS Label Switching
Table of Contents
1. MPLS Traffic Engineering Introduction
Traditional IP routing always follows the shortest path based on routing protocol metrics.
This can create:
- Congestion
- Uneven bandwidth usage
- Suboptimal routing
- High latency
MPLS Traffic Engineering solves these problems by allowing administrators to manually control packet forwarding paths.
MPLS TE Cost Function
$$ Path_{optimal}=Minimum(Bandwidth\\ Constraint+Delay+Cost) $$Traffic Engineering selects paths based on:
- Bandwidth availability
- Administrative policy
- Delay
- Link attributes
Network Topology
R1 -------- R3 -------- R4 -------- R5
\ /
\ /
\ /
R2
The objective is:
- Configure MPLS Core
- Enable MPLS TE
- Build TE Tunnel from R1 to R5
- Force traffic through R3 and R4
- Enable Fast Reroute protection
- Create backup path via R2
2. Task 1 - Configure OSPF Between All SP Routers
OSPF provides the IGP foundation required for MPLS Traffic Engineering.
Every router advertises:
- Loopback interfaces
- Transit links
- Core connectivity
Why Loopback Router IDs?
Loopbacks are stable and never go down unless administratively shut down.
Router ID Stability
$$ Reliable\\ RouterID = Loopback\\ Interface $$This ensures stable:
- LDP neighbors
- OSPF neighbors
- TE tunnels
- RSVP signaling
R1 OSPF Configuration
router ospf 1 router-id 1.1.1.1 network 1.1.1.1 0.0.0.0 area 0 network 192.1.13.1 0.0.0.0 area 0
R2 OSPF Configuration
router ospf 1 router-id 2.2.2.2 network 2.2.2.2 0.0.0.0 area 0 network 192.1.23.2 0.0.0.0 area 0 network 192.1.24.2 0.0.0.0 area 0
R3 OSPF Configuration
router ospf 1 router-id 3.3.3.3 network 3.3.3.3 0.0.0.0 area 0 network 192.1.13.3 0.0.0.0 area 0 network 192.1.23.3 0.0.0.0 area 0 network 192.1.34.3 0.0.0.0 area 0
R4 OSPF Configuration
router ospf 1 router-id 4.4.4.4 network 4.4.4.4 0.0.0.0 area 0 network 192.1.24.4 0.0.0.0 area 0 network 192.1.34.4 0.0.0.0 area 0 network 192.1.45.4 0.0.0.0 area 0
R5 OSPF Configuration
router ospf 1 router-id 5.5.5.5 network 5.5.5.5 0.0.0.0 area 0 network 192.1.45.5 0.0.0.0 area 0
OSPF Neighbor Verification
R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 3.3.3.3 1 FULL/BDR 00:00:31 192.1.13.3 Ethernet0/0
3. Task 2 - Configure MPLS LDP
LDP stands for Label Distribution Protocol.
LDP distributes MPLS labels between neighboring routers.
MPLS Label Switching Formula
$$ Incoming\\ Label \rightarrow Outgoing\\ Label $$Routers use:
- LFIB
- LIB
- FEC mappings
Why Use Loopback as LDP Router ID?
Loopbacks provide stable label-switched paths.
R1 MPLS Configuration
mpls ldp router-id Loopback0 interface Ethernet0/0 mpls ip
R2 MPLS Configuration
mpls ldp router-id Loopback0 interface Ethernet0/0 mpls ip interface Ethernet0/1 mpls ip
R3 MPLS Configuration
mpls ldp router-id Loopback0 interface Ethernet0/0 mpls ip interface Ethernet0/1 mpls ip interface Ethernet0/2 mpls ip
R4 MPLS Configuration
mpls ldp router-id Loopback0 interface Ethernet0/0 mpls ip interface Ethernet0/1 mpls ip interface Ethernet0/2 mpls ip
R5 MPLS Configuration
mpls ldp router-id Loopback0 interface Ethernet0/0 mpls ip
LDP Neighbor Verification
R1#show mpls ldp neighbor Peer LDP Identifier: 3.3.3.3:0 TCP connection: 3.3.3.3.646 State: Oper
4. Task 3 - Enable MPLS Traffic Engineering
Traffic Engineering extensions allow OSPF to advertise:
- Available bandwidth
- Administrative groups
- TE metrics
- Link constraints
Available Bandwidth Formula
$$ Available\\ Bandwidth= Total\\ Link\\ Capacity - Reserved\\ Bandwidth $$R1 MPLS TE Configuration
mpls traffic-eng tunnels router ospf 1 mpls traffic-eng router-id Loopback0 mpls traffic-eng area 0
R2 R3 R4 R5 MPLS TE Configuration
Apply identical MPLS TE configuration on all remaining routers.
mpls traffic-eng tunnels router ospf 1 mpls traffic-eng router-id Loopback0 mpls traffic-eng area 0
OSPF TE Database Verification
R1#show ip ospf mpls traffic-eng link Area 0 Link ID : 192.1.13.3 Maximum Bandwidth : 512000 Unreserved Bandwidth : 512000
5. Task 4 - Configure RSVP Bandwidth Reservation
RSVP reserves bandwidth along MPLS TE tunnel paths.
This ensures guaranteed forwarding resources.
RSVP Reservation Formula
$$ Reserved\\ BW \leq Available\\ BW $$If:
$$ Reserved\\ BW > Available\\ BW $$Tunnel setup fails.
R1 RSVP Configuration
interface Ethernet0/0 mpls traffic-eng tunnels ip rsvp bandwidth 512
R2 RSVP Configuration
interface Ethernet0/0 mpls traffic-eng tunnels ip rsvp bandwidth 512 interface Ethernet0/1 mpls traffic-eng tunnels ip rsvp bandwidth 512
R3 RSVP Configuration
interface Ethernet0/0 mpls traffic-eng tunnels ip rsvp bandwidth 512 interface Ethernet0/1 mpls traffic-eng tunnels ip rsvp bandwidth 512 interface Ethernet0/2 mpls traffic-eng tunnels ip rsvp bandwidth 192
R4 RSVP Configuration
interface Ethernet0/0 mpls traffic-eng tunnels ip rsvp bandwidth 512 interface Ethernet0/1 mpls traffic-eng tunnels ip rsvp bandwidth 512 interface Ethernet0/2 mpls traffic-eng tunnels ip rsvp bandwidth 192
R5 RSVP Configuration
interface Ethernet0/0 mpls traffic-eng tunnels ip rsvp bandwidth 512
6. Task 5 - Configure MPLS TE Tunnel from R1 to R5
The tunnel must follow:
R1 → R3 → R4 → R5
This is achieved using an Explicit Path.
Explicit Path Formula
$$ Tunnel\\ Path= \{R1,R3,R4,R5\} $$R1 Tunnel Configuration
interface Tunnel1 ip unnumbered Loopback0 tunnel destination 5.5.5.5 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-R5 tunnel mpls traffic-eng fast-reroute ip explicit-path name R1-R5 enable next-address 3.3.3.3 next-address 4.4.4.4 next-address 5.5.5.5
What Does Autoroute Announce Do?
Autoroute announce injects the tunnel into the routing table.
Traffic automatically prefers the TE tunnel.
Tunnel Verification
R1#show mpls traffic-eng tunnels Name: Tunnel1 Destination: 5.5.5.5 Bandwidth: 128 State: Up Path: Explicit
7. Task 6 - Configure Backup Tunnel on R3
Fast Reroute protects traffic when the R3-R4 link fails.
The backup path is:
R3 → R2 → R4
Fast Reroute Protection Formula
$$ Recovery\\ Time < 50ms $$Fast Reroute minimizes packet loss during failures.
R3 Backup Tunnel Configuration
interface Tunnel1 ip unnumbered Loopback0 tunnel destination 4.4.4.4 tunnel mode mpls traffic-eng tunnel mpls traffic-eng priority 4 4 tunnel mpls traffic-eng bandwidth 128 tunnel mpls traffic-eng path-option 1 explicit name R3-R4 ip explicit-path name R3-R4 enable next-address 2.2.2.2 next-address 4.4.4.4 interface Ethernet0/1 mpls traffic-eng backup tunnel 1
Fast Reroute Database Verification
R3#show mpls traffic-eng fast-reroute database Protected Interface: Ethernet0/1 Backup Tunnel: Tunnel1 State: Ready
8. Important Verification Commands
| Purpose | Command |
|---|---|
| OSPF Neighbors | show ip ospf neighbor |
| LDP Neighbors | show mpls ldp neighbor |
| TE Tunnels | show mpls traffic-eng tunnels |
| RSVP Interfaces | show ip rsvp interface |
| FRR Database | show mpls traffic-eng fast-reroute database |
| TE Topology | show ip ospf mpls traffic-eng link |
9. MPLS Traffic Engineering Mathematics
Bandwidth Utilization
$$ Utilization= \frac{Reserved\\ Bandwidth}{Total\\ Bandwidth} \times 100 $$RSVP Constraint Formula
$$ Path= \sum ConstraintsSatisfied $$Label Switching Equation
$$ Incoming\\ Label \rightarrow Swap \rightarrow Outgoing\\ Label $$Traffic Engineering Metric
$$ TE\\ Cost= Bandwidth+Delay+Administrative\\ Weight $$10. Troubleshooting MPLS TE
| Problem | Cause | Solution |
|---|---|---|
| Tunnel Down | No RSVP bandwidth | Enable RSVP reservation |
| LDP Failure | No MPLS IP | Enable mpls ip |
| OSPF TE Missing | TE Area Disabled | Enable mpls traffic-eng area |
| Backup Tunnel Inactive | Wrong protected interface | Verify backup tunnel command |
| Path Failure | Explicit path incorrect | Verify next-address sequence |
💡 Key Takeaways
- OSPF provides MPLS reachability
- LDP distributes MPLS labels
- RSVP reserves bandwidth
- TE tunnels create engineered paths
- Explicit paths override shortest path routing
- Fast Reroute provides sub-50ms recovery
- Backup tunnels improve core resiliency
- MPLS TE optimizes WAN utilization
11. Related Articles
- Cisco Nexus FEX and vPC Configuration
- Cisco Nexus vPC Peer Gateway and VDC
- Cisco Nexus VRRP Configuration Guide
- Cisco Nexus EIGRP and HSRP
- Cisco Nexus vPC and LACP Configuration
- Complete Cisco Nexus VXLAN EVPN
- Complete Cisco Nexus VXLAN
- Complete Cisco Nexus Multicast
Final Conclusion
This MPLS Traffic Engineering lab demonstrated complete deployment of:
- OSPF Core Routing
- MPLS LDP
- MPLS Traffic Engineering
- RSVP Reservation
- Explicit TE Paths
- Fast Reroute Protection
- Backup Tunnel Engineering
Understanding MPLS TE is extremely important for:
- Service Provider Networks
- Large WAN Deployments
- Mission Critical Applications
- Low Latency Networks
- High Availability Designs
MPLS Traffic Engineering remains one of the most powerful technologies for advanced WAN optimization and resilient packet forwarding.
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