1. Kireeti Kompella Juniper Networks
MPLS-based Layer 2 VPNs
Kireeti Kompella
Juniper Networks

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Agenda
Introduction
Traditional Layer 2 VPNs
MPLS-based Layer 2 VPNs
Layer 3 VPNs
Details
Provisioning
Signaling
Topology
Future work
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3. Traditional (Layer 2) VPNs
Router
Frame Relay/
ATM Switch
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4. Traditional (Layer 2) VPNs
Provider network technology dictated by VPN services
Frame switches? ATM switches?
Provisioning – complex for provider
Topology dictated by cost rather than traffic patterns
Multiple networks – adds to provider’s administrative burden
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Question
Can we
Decouple edge (customer-facing) technology from core technology?
Have a single network infrastructure for all desired services?
Simplify provisioning?
Appropriate signaling mechanisms?
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Answer
MPLS is layer 2 agnostic
POS in the core
MPLS offers several services
One infrastructure does it all
MPLS has signaling
RSVP, LDP, BGP work great, and are extensible
MPLS has label stacking
Provision once, and use same LSP for multiple purposes
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MPLS-Based Layer 2 VPNs
Traditional Layer 2 VPN from customer’s point-of-view
Layer 3 independent
Provider not responsible for routing
MPLS transport in provider network
Decouples edge and core technologies
Auto-provisioning VPN
Single network architecture for both Internet traffic and VPN traffic
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MPLS-Based Layer 2 VPNs
CE G
CE B
CE A
CE E
CE D
CE C
CE F
PE 1
PE 2
PE 3
PE 4
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Layer 3 VPNs
SP participates in customers’ routing
Out-sourced routing
Added SP responsibilities
Value-added service ~ cost structure
BGP MPLS VPNs – mature technology
QoS/CoS, Carrier of Carriers, inter-SP VPNs
Virtual routers
Migration may take some work
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Provisioning
CE G
CE B
CE A
CE E
CE D
CE C
CE F
PE 1
PE 2
PE 3
PE 4
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11. Provisioning the Network
PE-to-PE MPLS LSPs
Key: signaling
LDP LSPs
RSVP-TE LSPs
LDP over RSVP tunneling
Fully-meshed Traffic Engineered core
Edge-to-edge LDP LSPs
Used for many services – IP, L2 VPNs, L3 VPNs, differentiated services
Provisioned independent of Layer 2 VPNs!
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Provisioning a VPN
Key: signaling
Auto-discovery of members, auto-assignment of inter-member circuits
Flexible VPN topology
Signaling using LDP or BGP
O(N) configuration for the whole VPN
Could be more for complex topologies
O(1) configuration to add a site
“Overprovision” DLCIs at customer sites
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13. Provisioning Customer Sites
List of DLCIs, one for each other site, some spare (over-provisioning)
DLCIs independently numbered at each site
LMI, inverse ARP and/or routing protocols for auto-discovery and learning addresses
No changes as VPN membership changes (until over-provisioning runs out)
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VPN Signaling
Signaling through either BGP or LDP
Compact representation of mapping of layer 2 address to inner label
PE says: “CE k is in Blue VPN; label base 1000”
This info sent to all members of Blue VPN
CE # 0 uses label to reach CE k
CE # 1 uses label to reach CE k
Etc.
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Information Signaled
Compact representation means one “routing entry” per CE per VPN in BGP/LDP
Same info sent to each peer
One “route” per CE per VPN in each PE’s forwarding table
200 CEs per PE, 500 PEs in network means total VPN routes in entire network
Can easily be held by a single route reflector
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VPN Topologies
Arbitrary topologies possible; common ones such as full mesh and hub-and-spoke easy to configure
BGP communities used to configure arbitrary topologies in BGP signaling
“Connectivity” parameter serves similar purpose in LDP signaling
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Future Work
Layer 2 technologies
VLANs
MPLS as layer 2 to CE
Decouples access technology
Carrier of carriers model, inter-SP VPNs, QoS/CoS support
Reduce dependency on “over-provisioning”
Security
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Summary
Benefits to customer
MPLS-based Layer 2 VPNs identical to Layer 2 VPNs from customers’ perspective
Familiar paradigm
Easy to migrate
OSPF handled naturally
Rely on SP only for connectivity
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Summary
Benefits to SP
Single network infrastructure for all services: L2 VPNs, L3 VPNs, Traffic Engineering, DiffServ
Auto-provisioning: VPN members discover each other, signal required DLCIs
Layer 3 and routing independent
Good scaling characteristics
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20. Thank you!