MPLS: The Magic
Behind the Myths
Grenville Armitage (author)
Scott Crosby (presenter)
Problems with IP
 No Quality of Service
 Necessary for converged network
 Realtime voice
 Best-effort data
 High priority transactions (ATM, control, VC, …)
 Performance Scalability
 Expensive prefix match for each packet
 Traffic Engineering
Problems with IP
 Tunneling
 Tunnel IP over non-IP intermediate
 IP over IP over ATM?
IP Network
IP Network
ATM
IP Network
IP Network
Problems with IP
 Tunneling
 Tunnel IP over non-IP intermediate
 Virtual Private Network
Abercr. CS
IP Network
Abercr. EE
IP Network
Duncan EE
IP Network
Duncan CS
IP Network
Problems with IP
 Tunneling
 Tunnel IP over non-IP intermediate
 Virtual Private Network
 Traffic Engineering
IP Network
IP Network
IP Network
IP Network
What is MPLS?
 Virtual circuit layer underneath IP
 Virtual circuit = virtual wire = label switched path
IP Network
(Voice)
IP Network
(ATM)
IP Network
(Data)
MPLS
(Virtual Point-to-Point Circuits)
Physical Infrastructure
(Point-to-Point Circuits)
What is MPLS?
 Offer service above IP
 Converged network
 Realtime voice
 Best-effort data
 High priority transactions (ATM, control …)
 On the same physical infrastructure
 Hop-by-hop QoS differentiation
How Does MPLS Work?
 Packets are tagged and routed based on tags.
 All traffic with the same label treated the same
13
5
IP Routing
Layer
Payload
Payload
IP Routing
Layer
LSR
Payload
Payload
13
Payload
5
Payload
LER
LER
13
Payload
Payload
5
Payload
Payload
Other Features of MPLS
 Tag forwarding distinct from IP forwarding
 May make non-shortest paths
 Tag routing linked to IP routing
IP Forwarding
LER
(Perform Tagging)
LSR Cloud
(Forward by tag)
IP Forwarding
LER
(Remove Tag)
LSR Cloud
(Forward by tag)
MPLS Header
 Lightweight




8 bit TTL
20 bit label tag
3 bit QoS tag
1 bit stack
 Indicates last LSR tag
 Allows heirarchial tagging
13
Payload
13
5 13
Payload
8 13
Payload
Payload
Provisioning vs. Signalling
 Signalling
 Seconds
 Provisioning
 Minutes to days
 Separate control message protocol
 Distribute labels and forwarding info
 RSVP
 Label Distribution Protocol
Comparing MPLS to IP
 IP over MPLS vs IP only





Qos
Performance
Tunneling
VPN
Traffic Engineering
MPLS vs IP: QoS
 MPLS
 Per hop QoS
 Using labels to prioritize
 20 bit identifier space
 IP
 Per hop QoS
 Use IP&TCP header
 104 bit identifier space
MPLS vs IP: Performance
 MPLS
 Forward on short tags
 Not prefix match on address
 IP
 Routers can forward at gigabit/s
MPLS vs IP: Tunneling
 MPLS
 Lightweight tunnels
 32 bit header
 IP
 Heavyweight tunnels
 ~160 (?) bit header
MPLS vs IP: VPN
 MPLS
 Lightweight
 32 bit header
 No security
 IP
 Heavyweight
 ~160 (?) bit header
 No security
 (without IPSEC)
MPLS vs IP: Traffic Engin.
 MPLS




Arbitrary (non-shortest) paths
Virtual circuits
MPLS routing linked to IP routing
Flexible aggregation
 IP
 Route announcement manipulation
 Path cost manipulation
MPLS vs IP: Future QoS
 MPLS
 Propagate QoS between networks
 RSVP
 IP
 Propagate QoS between networks
 RSVP
Compelling Advantages
 Traffic engineering
 Management engine
 Connectivity
 Policy
 Constraint based routing
 Construct virtual topology
 LSP’s
 Labels