Complete MPLS VPLS Configuration Guide Using Cisco CSR Routers
This complete educational tutorial explains how to configure MPLS VPLS using Cisco CSR routers in a service provider environment. We will configure OSPF, MPLS LDP, VPLS Virtual Forwarding Instances (VFI), Bridge Domains, VLAN encapsulation, and EIGRP routing across customer sites.
🎯 What You Will Learn
- Understanding MPLS fundamentals
- How Label Distribution Protocol works
- OSPF in MPLS Core
- VPLS architecture explained
- Bridge Domains in MPLS
- Virtual Forwarding Instances
- Layer 2 VPN technologies
- EIGRP over VPLS
- PE and CE router roles
- Verification and troubleshooting
Table of Contents
1. MPLS Fundamentals
MPLS stands for Multiprotocol Label Switching.
MPLS is a forwarding technology that uses labels instead of traditional Layer 3 routing lookups.
Instead of routers examining destination IP addresses at every hop, MPLS routers use labels to forward packets quickly and efficiently.
MPLS Forwarding Formula
$$ Forwarding = Label\\ Lookup + LFIB\\ Action $$Where:
- LFIB = Label Forwarding Information Base
- Labels reduce routing complexity
- Forwarding becomes faster
2. Understanding VPLS
VPLS stands for Virtual Private LAN Service.
VPLS allows geographically separated customer sites to behave as if they are connected to the same Ethernet switch.
This creates a Layer 2 VPN service across an MPLS provider backbone.
VPLS Switching Logic
$$ Remote\\ Site = Same\\ Broadcast\\ Domain $$Meaning:
$$ MAC\\ Frames \rightarrow MPLS\\ Backbone \rightarrow Remote\\ CE $$3. OSPF in MPLS Core
OSPF is used as the Interior Gateway Protocol inside the provider backbone.
OSPF distributes loopback and core interface reachability between all Provider routers.
Shortest Path Formula
$$ SPF = Min(Cost) $$OSPF uses Dijkstra’s Shortest Path First algorithm.
4. MPLS LDP Explained
LDP stands for Label Distribution Protocol.
LDP distributes MPLS labels between routers.
Every MPLS router advertises labels for reachable prefixes.
Label Mapping Formula
$$ FEC \rightarrow Label $$Where:
- FEC = Forwarding Equivalence Class
- Each prefix receives a label
5. Network Topology
MPLS CORE
CSR1 -------- CSR2
\\ /
\\ /
\\ /
CSR3
| | |
R4 R5 R6
In this topology:
- CSR1, CSR2, CSR3 are Provider Edge/Core routers
- R4, R5, R6 are Customer Edge routers
- OSPF runs in provider core
- EIGRP runs between customer routers
- VPLS extends Layer 2 connectivity
6. Task 1 - Configure MPLS Core Routers
We first configure the Service Provider core routers.
This includes:
- IP addressing
- OSPF routing
- MPLS LDP
- Loopback interfaces
Why Loopbacks Matter
Loopback interfaces provide stable MPLS LDP router IDs.
LDP Stability Formula
$$ Stable\\ RouterID = Loopback\\ Interface $$Because:
$$ Loopback\\ Interfaces \neq Physical\\ Link\\ Failure $$CSR1 Configuration
Code Example
mpls ldp router-id Loopback10
This command ensures stable LDP identification.
CSR1 interface Gig1 ip address 192.1.12.1 255.255.255.0 mpls ip no shut ! interface Gig2 ip address 192.1.13.1 255.255.255.0 mpls ip no shut ! interface Loopback10 ip address 1.1.1.1 255.255.255.255 ! mpls ldp router-id Loopback10 ! router ospf 1 router-id 0.0.0.1 network 192.1.12.0 0.0.0.255 area 0 network 192.1.13.0 0.0.0.255 area 0 network 1.0.0.0 0.255.255.255 area 0
Detailed Explanation
The command:
mpls ip
enables MPLS forwarding on interfaces.
OSPF advertises all provider backbone networks.
Loopback10 becomes the LDP router ID.
CSR2 Configuration
CSR2 interface Gig1 ip address 192.1.12.2 255.255.255.0 mpls ip no shut ! interface Gig2 ip address 192.1.23.2 255.255.255.0 mpls ip no shut ! interface Loopback10 ip address 2.2.2.2 255.255.255.255 ! mpls ldp router-id Loopback10 ! router ospf 1 router-id 0.0.0.2 network 192.1.12.0 0.0.0.255 area 0 network 192.1.23.0 0.0.0.255 area 0 network 2.0.0.0 0.255.255.255 area 0
CSR3 Configuration
CSR3 interface Gig1 ip address 192.1.23.3 255.255.255.0 mpls ip no shut ! interface Gig2 ip address 192.1.13.3 255.255.255.0 mpls ip no shut ! interface Loopback10 ip address 3.3.3.3 255.255.255.255 ! mpls ldp router-id Loopback10 ! router ospf 1 router-id 0.0.0.3 network 192.1.13.0 0.0.0.255 area 0 network 192.1.23.0 0.0.0.255 area 0 network 3.0.0.0 0.255.255.255 area 0
7. Task 2 - Configure VPLS
Now we configure the Layer 2 VPN service using VPLS.
All customer sites become members of the same Ethernet segment.
Bridge Domain Formula
$$ Broadcast\\ Domain = Shared\\ Ethernet\\ Segment $$All devices in Bridge Domain 100 belong to the same Layer 2 network.
Understanding VFI
VFI stands for Virtual Forwarding Instance.
The VFI maintains pseudowire relationships between PE routers.
Pseudowire Logic
$$ PE_1 \leftrightarrow PE_2 \leftrightarrow PE_3 $$All PE routers form a full mesh pseudowire topology.
CSR1 VPLS Configuration
Code Example
bridge-domain 100
This command associates Ethernet frames with Bridge Domain 100.
CSR1 interface GigabitEthernet3 no shut service instance 1 ethernet encapsulation dot1q 10 bridge-domain 100 ! l2 vfi CUSTA manual vpn id 111 bridge-domain 100 neighbor 3.3.3.3 encapsulation mpls neighbor 2.2.2.2 encapsulation mpls
Configuration Explanation
- VLAN 10 carries customer traffic
- Bridge Domain 100 groups customer interfaces
- VFI CUSTA builds MPLS pseudowires
- Neighbors are remote PE routers
CSR2 VPLS Configuration
CSR2 interface GigabitEthernet3 no shut service instance 1 ethernet encapsulation dot1q 10 bridge-domain 100 ! l2 vfi CUSTA manual vpn id 111 bridge-domain 100 neighbor 1.1.1.1 encapsulation mpls neighbor 3.3.3.3 encapsulation mpls
CSR3 VPLS Configuration
CSR3 interface GigabitEthernet3 no shut service instance 1 ethernet encapsulation dot1q 10 bridge-domain 100 ! l2 vfi CUSTA manual vpn id 111 bridge-domain 100 neighbor 1.1.1.1 encapsulation mpls neighbor 2.2.2.2 encapsulation mpls
8. Task 3 - Configure Customer Edge Routers
Now we configure CE routers.
Customer traffic uses VLAN 10 subinterfaces.
EIGRP exchanges customer loopback routes.
EIGRP Metric Formula
$$ Metric = 256 \times \left( \frac{10^7}{Bandwidth} + Delay \right) $$EIGRP selects paths using bandwidth and delay.
R4 Configuration
R4 interface E0/0 no shut ! interface E0/0.1 encapsulation dot1q 10 ip address 10.10.10.4 255.255.255.0 no shut ! interface loopback0 ip address 10.4.4.4 255.255.255.0 ! router eigrp 100 network 10.0.0.0
R5 Configuration
R5 interface E0/0 no shut ! interface E0/0.1 encapsulation dot1q 10 ip address 10.10.10.5 255.255.255.0 no shut ! interface loopback0 ip address 10.5.5.5 255.255.255.0 ! router eigrp 100 network 10.0.0.0
R6 Configuration
R6 interface E0/0 no shut ! interface E0/0.1 encapsulation dot1q 10 ip address 10.10.10.6 255.255.255.0 no shut ! interface loopback0 ip address 10.6.6.6 255.255.255.0 ! router eigrp 100 network 10.0.0.0
Why EIGRP Works Across VPLS
VPLS extends Layer 2 connectivity.
From the CE perspective:
- All routers appear locally connected
- EIGRP multicast packets work normally
- ARP operates normally
- Broadcast traffic crosses MPLS pseudowires
9. Verification Commands
Verify OSPF Neighbors
show ip ospf neighbor
Verify MPLS LDP Neighbors
show mpls ldp neighbor
Verify MPLS Forwarding Table
show mpls forwarding-table
Verify VPLS
show l2vpn vfi
Verify EIGRP Neighbors
show ip eigrp neighbors
Expected CLI Output
CSR1#show mpls ldp neighbor Peer LDP Ident: 2.2.2.2:0 TCP connection: 2.2.2.2.646 Peer LDP Ident: 3.3.3.3:0 TCP connection: 3.3.3.3.646
10. Troubleshooting MPLS VPLS
| Problem | Cause | Solution |
|---|---|---|
| No MPLS labels | LDP not enabled | Enable mpls ip |
| No OSPF adjacency | Incorrect network statement | Verify OSPF config |
| VPLS down | Neighbor mismatch | Check VFI neighbors |
| No EIGRP routes | VLAN mismatch | Verify VLAN encapsulation |
| No MAC learning | Bridge domain issue | Verify BD membership |
11. MPLS and VPLS Mathematics
Packet Encapsulation Formula
$$ Ethernet + MPLS\\ Label + IP + Payload $$Pseudowire Scalability Formula
$$ PW = \frac{n(n-1)}{2} $$Where:
- \(n\) = number of PE routers
For:
$$ n=3 $$Then:
$$ PW = \frac{3(3-1)}{2}=3 $$Three pseudowires are required.
OSPF Cost Formula
$$ Cost = \frac{Reference\\ Bandwidth}{Interface\\ Bandwidth} $$EIGRP Feasibility Condition
$$ Reported\\ Distance < Feasible\\ Distance $$💡 Key Takeaways
- MPLS uses labels for forwarding
- OSPF provides provider core reachability
- LDP distributes MPLS labels
- VPLS creates Layer 2 VPN services
- Bridge Domains extend Ethernet networks
- VFI builds MPLS pseudowires
- EIGRP runs transparently across VPLS
- Loopbacks provide stable router IDs
12. Related Networking Articles
- Cisco Nexus FEX and vPC Configuration
- Cisco Nexus vPC Peer Gateway and VDC
- Cisco Nexus VRRP Configuration Guide
- Complete Cisco Nexus VXLAN EVPN
- Complete Cisco Nexus VXLAN
- Complete Cisco Nexus Multicast
- Complete Cisco Nexus BGP Authentication
- Complete Cisco Nexus OSPF
- Complete Cisco Nexus EIGRP
- Complete Cisco Nexus Static Routing Lab
Final Conclusion
This complete MPLS VPLS tutorial demonstrated how service providers create scalable Layer 2 VPN services using MPLS and pseudowires.
We configured:
- OSPF in the provider backbone
- MPLS LDP label distribution
- Bridge Domains
- Virtual Forwarding Instances
- VLAN encapsulation
- EIGRP across customer sites
- Layer 2 VPN connectivity
Understanding MPLS VPLS is critical for network engineers working in enterprise WANs, data centers, and service provider environments.
No comments:
Post a Comment