MPLS: The Magic Behind the Myths

1
MPLS The Magic Behind the Myths

• Grenville Armitage (author)
• Scott Crosby (presenter)

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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

3
Problems with IP

• Tunneling
• Tunnel IP over non-IP intermediate
• IP over IP over ATM?

IP Network
IP Network
ATM
IP Network
IP Network
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Problems with IP

• Tunneling
• Tunnel IP over non-IP intermediate
• Virtual Private Network

Duncan EE IP Network
Abercr. CS IP Network
Abercr. EE IP Network
Duncan CS IP Network
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Problems with IP

• Tunneling
• Tunnel IP over non-IP intermediate
• Virtual Private Network
• Traffic Engineering

IP Network
IP Network
IP Network
IP Network
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What is MPLS?

• Virtual circuit layer underneath IP
• Virtual circuit virtual wire label switched
  path

IP Network (ATM)
IP Network (Voice)
IP Network (Data)
MPLS (Virtual Point-to-Point Circuits)
Physical Infrastructure (Point-to-Point Circuits)
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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

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How Does MPLS Work?

• Packets are tagged and routed based on tags.
• All traffic with the same label treated the same

IP Routing Layer
IP Routing Layer
LSR
Payload
Payload
LER
LER
Payload
Payload
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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)
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MPLS Header

• Lightweight
• 8 bit TTL
• 20 bit label tag
• 3 bit QoS tag
• 1 bit stack
• Indicates last LSR tag
• Allows heirarchial tagging

Payload
13
Payload
13
8
Payload
13
5
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Provisioning vs. Signalling

• Signalling
• Seconds
• Provisioning
• Minutes to days
• Separate control message protocol
• Distribute labels and forwarding info
• RSVP
• Label Distribution Protocol

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Comparing MPLS to IP

• IP over MPLS vs IP only
• Qos
• Performance
• Tunneling
• VPN
• Traffic Engineering

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MPLS vs IP QoS

• MPLS
• Per hop QoS
• Using labels to prioritize
• 20 bit identifier space
• IP
• Per hop QoS
• Use IPTCP header
• 104 bit identifier space

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MPLS vs IP Performance

• MPLS
• Forward on short tags
• Not prefix match on address
• IP
• Routers can forward at gigabit/s

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MPLS vs IP Tunneling

• MPLS
• Lightweight tunnels
• 32 bit header
• IP
• Heavyweight tunnels
• 160 (?) bit header

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MPLS vs IP VPN

• MPLS
• Lightweight
• 32 bit header
• No security
• IP
• Heavyweight
• 160 (?) bit header
• No security
• (without IPSEC)

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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

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MPLS vs IP Future QoS

• MPLS
• Propagate QoS between networks
• RSVP
• IP
• Propagate QoS between networks
• RSVP

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Compelling Advantages

• Traffic engineering
• Management engine
• Connectivity
• Policy
• Constraint based routing
• Construct virtual topology
• LSPs
• Labels