MPLS: The Magic Behind the Myths Grenville Armitage (author) Scott Crosby (presenter)

Problems with IP No Quality of Service No Quality of Service Necessary for converged network Necessary for converged network Realtime voice Realtime voice Best-effort data Best-effort data High priority transactions (ATM, control, VC, …) High priority transactions (ATM, control, VC, …) Performance Scalability Performance Scalability Expensive prefix match for each packet Expensive prefix match for each packet Traffic Engineering Traffic Engineering

Problems with IP Tunneling Tunneling Tunnel IP over non-IP intermediate Tunnel IP over non-IP intermediate IP over IP over ATM? IP over IP over ATM? IP Network ATM

Problems with IP Tunneling Tunneling Tunnel IP over non-IP intermediate Tunnel IP over non-IP intermediate Virtual Private Network Virtual Private Network Abercr. CS IP Network Duncan EE IP Network Abercr. EE IP Network Duncan CS IP Network

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

What is MPLS? Virtual circuit layer underneath IP Virtual circuit layer underneath IP Virtual circuit = virtual wire = label switched path 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)

What is MPLS? Offer service above IP Offer service above IP Converged network Converged network Realtime voice Realtime voice Best-effort data Best-effort data High priority transactions (ATM, control …) High priority transactions (ATM, control …) On the same physical infrastructure On the same physical infrastructure Hop-by-hop QoS differentiation Hop-by-hop QoS differentiation

How Does MPLS Work? Packets are tagged and routed based on tags. Packets are tagged and routed based on tags. All traffic with the same label treated the same All traffic with the same label treated the same LER IP Routing Layer IP Routing Layer LSR Payload 13 Payload 5 13Payload13 Payload 5 5

Other Features of MPLS Tag forwarding distinct from IP forwarding Tag forwarding distinct from IP forwarding May make non-shortest paths May make non-shortest paths Tag routing linked to IP routing 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 Lightweight 8 bit TTL 8 bit TTL 20 bit label tag 20 bit label tag 3 bit QoS tag 3 bit QoS tag 1 bit stack 1 bit stack Indicates last LSR tag Indicates last LSR tag Allows heirarchial tagging Allows heirarchial tagging Payload13 Payload138Payload135 Payload13

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

Comparing MPLS to IP IP over MPLS vs IP only IP over MPLS vs IP only Qos Qos Performance Performance Tunneling Tunneling VPN VPN Traffic Engineering Traffic Engineering

MPLS vs IP: QoS MPLS MPLS Per hop QoS Per hop QoS Using labels to prioritize Using labels to prioritize 20 bit identifier space 20 bit identifier space IP IP Per hop QoS Per hop QoS Use IP&TCP header Use IP&TCP header 104 bit identifier space 104 bit identifier space

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

MPLS vs IP: Tunneling MPLS MPLS Lightweight tunnels Lightweight tunnels 32 bit header 32 bit header IP IP Heavyweight tunnels Heavyweight tunnels ~160 (?) bit header ~160 (?) bit header

MPLS vs IP: VPN MPLS MPLS Lightweight Lightweight 32 bit header 32 bit header No security No security IP IP Heavyweight Heavyweight ~160 (?) bit header ~160 (?) bit header No security No security (without IPSEC) (without IPSEC)

MPLS vs IP: Traffic Engin. MPLS MPLS Arbitrary (non-shortest) paths Arbitrary (non-shortest) paths Virtual circuits Virtual circuits MPLS routing linked to IP routing MPLS routing linked to IP routing Flexible aggregation Flexible aggregation IP IP Route announcement manipulation Route announcement manipulation Path cost manipulation Path cost manipulation

MPLS vs IP: Future QoS MPLS MPLS Propagate QoS between networks Propagate QoS between networks RSVP RSVP IP IP Propagate QoS between networks Propagate QoS between networks RSVP RSVP

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