MPLS TE Overview Understanding MPLS TE Components 2006

MPLS TE Overview Understanding MPLS TE Components © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -1

Outline • Overview • Traffic Tunnels: Concepts • Traffic Tunnels: Characteristics • Traffic Tunnels: Attributes • Network Links and Link Attributes • Constraint-Based Path Computation • TE Processes • Role of RSVP in Path Setup and Trunk Admission Control • Forwarding Traffic to a Tunnel • Summary © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -2

Traffic Tunnels: Concepts The concept of MPLS TE traffic tunnels was introduced to overcome the limitations of hop-byhop IP routing: • A tunnel is an aggregation of traffic flows that are placed inside a common MPLS label-switched path. • Flows are then forwarded along a common path within a network. © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -3

Traffic Tunnels: Concepts (Cont. ) • Unidirectional single class of service model encapsulates all of the traffic between an ingress and an egress router. • Different classes of service model assigns traffic into separate tunnels with different characteristics. © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -4

Traffic Tunnels – Characteristics • A traffic tunnel is distinct from the MPLS LSP through which it traverses: – More than one TE tunnel can be defined between two points: • Each tunnel may pick the same or different paths through the network • Each tunnel will use different MPLS labels – A traffic tunnel can be moved from one path onto another based on resources in the network. • A traffic tunnel is configured by defining its required attributes and characteristics. © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -5

Traffic Tunnels – Attributes • Attributes are explicitly assigned through administrative action. • A traffic tunnel is characterized by: – Its ingress (headend) and egress (tailend) label switch routers – The forwarding equivalence class that is mapped onto it – A set of attributes that determine its characteristics © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -6

Traffic Tunnels–Attributes (Cont. ) The administrator enters the relevant information (attributes) at the headend of the traffic tunnel: • Traffic parameter—Resources required for tunnel (for example, required bandwidth) • Generic path selection and management—Path can be administratively specified or computed by the IGP • Resource class affinity—Include or exclude certain links for certain traffic tunnels • Adaptability—Should the traffic tunnel be reoptimized? • Priority and preemption—Importance of a traffic tunnel and possibility for a preemption of another tunnel • Resilience—Desired behavior under fault conditions © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -7

Network Links and Link Attributes Resource attributes (link availability) are configured locally on the router interfaces: • Maximum bandwidth – The amount of bandwidth available • Link affinity string – To allow the operator to administratively include or exclude links in path calculations • Constraint-based specific metric – TE default metric © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -8

Constraint-Based Path Computation • Constraint-based routing is demand-driven. • Resource-reservation-aware routing paradigm: – Based on criteria including, but not limited to, network topology – Calculated at the edge of a network: • Modified Dijkstra’s algorithm at tunnel headend (CSPF [Constraint-based SPF] or PCALC [path calculation]). • Output is a sequence of IP interface addresses (nexthop routers) between tunnel endpoints. © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -9

Constraint-Based Path Computation (Cont. ) • Constraint-based routing takes into account: – Policy constraints associated with the tunnel and physical links – Physical resource availability – Network topology state • Two types of tunnels can be established across those links with matching attributes: – Dynamic—Using the least-cost path computed by OSPF or IS-IS – Explicit—Definition of a path by using Cisco IOS configuration commands © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -10

Constraint-Based Path Computation (Cont. ) © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -11

Constraint-Based Path Computation (Cont. ) © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -12

Traffic Engineering Processes • Information distribution • Path selection and calculation • Path setup • Trunk admission control • Forwarding traffic on to tunnel • Path maintenance © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -13

Role of RSVP in Path Setup Procedures • When the path has been determined, a signaling protocol is needed: – To establish and maintain label-switched paths (LSPs) for traffic tunnels – For creating and maintaining resource reservation states across a network (bandwidth allocation) • The Resource Reservation Protocol (RSVP) was adopted by the MPLS workgroup of the IETF. © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -14

Path Setup with RSVP • When the path has been calculated, it must be signaled across the network. – Reserve any bandwidth to avoid “double booking” from other TE reservations. – Priority can be used to preempt low priority existing tunnels. • RSVP is used to set up TE LSP. – PATH message (from head to tail) carries LABEL_REQUEST. – RESV message (from tail to head) carries LABEL. • When RESV messages reaches headend, tunnel interface is up. • RSVP messages exist for LSP teardown and error signaling. © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -15

RSVP and Trunk Admission Control • On receipt of PATH message: – Router checks whethere is bandwidth available to honor the reservation. – If bandwidth is available, then RSVP is accepted. • On receipt of a RESV message: – Router actually reserves the bandwidth for the TE LSP. – If preemption is required, lower priority LSPs are torn down. • OSPF or IS-IS updates are triggered. © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -16

Forwarding Traffic to a Tunnel • IP routing is separate from LSP routing and does not see internal details of the LSP. • The traffic has to be mapped to the tunnel: – Static routing—The static route in the IP routing table points to an LSP tunnel interface. – Policy routing—The next-hop interface is an LSP tunnel. – Autoroute—SPF enhancement: • The headend sees the tunnel as a directly connected interface (for modified SPF only). • The default cost of a tunnel is equal to the shortest IGP metric regardless of the used path. © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -17

IP Forwarding Database Modification with Autoroute • Autoroute feature enables the headend to see the LSP as a directly connected interface: – This feature is used only for the SPF route determination, not for the constraint-based path computation. – All traffic directed to prefixes topologically behind the tunnel endpoint (tailend) is forwarded onto the tunnel. • Autoroute affects the headend only; other routers on the LSP path do not see the tunnel. • Tunnel is treated as a directly connected link to the tailend: – When tunnel tail is seen in PATH list during IGP SPF, replace outgoing physical interface with tunnel interface. – Inherit tunnel to all downstream neighbors of tailend. © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -18

Autoroute Topology (OSPF and ISIS) Tunnel 1: R 1 R 2 R 3 R 4 R 5 Tunnel 2: R 1 R 6 R 7 R 4 © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -19

Autoroute Topology (OSPF and ISIS) From R 1 Router Perspective: Next hop to R 5 is Tunnel 1. Next hop to R 4 and R 8 is Tunnel 2. All nodes behind tunnel are routed via tunnel. © 2006 Cisco Systems, Inc. All rights reserved. 20 MPLS v 2. 2— 8 -20

Summary • Traffic tunnels are configured with a set of resource requirements, such as bandwidth and priority. • CSPF augments the link cost by considering other factors such as bandwidth availability or link latency when choosing a path. • RSVP with TE extensions is used for establishing and maintaining LSPs. • TE tunnels do not appear in the IP routing table. © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -21

© 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 8 -22