1 Multi Protocol Label Switching Presented by: Petros Ioannou Dept. of Electrical and Computer Engineering, UCY

2 What is MPLS? Multi Protocol: Because it works with the Internet Protocol(IP), Asynchronous Transport Mode(ATM) and Frame Relay network protocols Label Switching: Because it use fixed length label switching similar to ATM or FR MPLS forwards packets based on labels MPLS simplifies and improve the forwarding function by introducing a connection oriented mechanism inside the connectionless IP networks Packets are switched, not routed

3 Why MPLS? IP Routing Disadvantages: Connectionless No QoS Each router has to make independent forwarding decisions based on the IP address Routing in Network Layer Slower than switching Usually designed to obtain shortest path Don’t take into account additional metrics

4 Why MPLS? Traffic Engineering

5 ATM Advantages: Connection oriented Supports QoS Fast packet switching with fixed length packets (cells) Integration of different traffic types (voice, data, video) ATM Disadvantages: Complex Expensive Not widely adopted

6 Why MPLS?

7 The Idea

8 MPLS Label Format MPLS uses a 32-bit label field: 20-bit label (a number) 3-bit experimental field (usually used to carry IP precedence value) 1-bit bottom-of-stack indicator (indicates whether this is the last label before the IP header) 8-bit TTL (equal to the TTL in the IP header)

9 MPLS Label Format

10 MPLS Terminology LSP: Label Switched Path An MPLS virtual circuit A path established before the data transmission starts FEC: Forwarding Equivalence Class A group of IP packets which are forwarded in the same manner (over the same path with the same forwarding treatment) LSR: Label Switching Router Any router in network who supports MPLS LER: Label Edge Router Resides at the edge of an MPLS network and assigns and removes the labels from the packets

11 MPLS Operation PUSHSWAPPOP Ingress Router Egress Router

12 Establishing a Label Switched Path Each LSR negotiates a label for each Forwarding Equivalence Class (FEC) with its neighbors using a distribution method The result of negotiation is a Label Information Base (LIB) Each LSR maintains a Label Information Base (LIB) and learns labels from there When next hop changes for a FEC, LSR will retrieve the label for the new next hop from the LIB

13 Label Distribution Protocols Label Distribution Protocol (LDP) Hop-by-Hop label distribution Follows IGP-OSPF best path No traffic engineering capabilities Highly scalable Best suited for apps using thousands of LSPs (VPNs) Resource Reservation Protocol with Traffic Engineering Extensions (RSVP- TE) End-to-End LSP signaling Enables different specifications on each path Less scalable Best suited for traffic engineering in the core Constraint-Based Routed LDP (CR-LDP) TE-capable LDP Never widely deployed

14 Label Distribution Protocol (LDP) A protocol which it is used to map FECs to labels In order to do that LDP sessions are established between LDP peers in the MPLS network LDP message types: discovery messages: announce and maintain the presence of an LSR in a network session messages: establish, maintain, and terminate sessions between LDP peers advertisement messages: create, change, and delete label mappings for FECs notification messages: provide advisory information and signal error information

15 Label Distribution Protocol (LDP)

16 Traffic Engineering A way to achieve required delay, grade-of- service and to meet policy requirements imposed by the network operator Traffic Engineering ensure available spare link capacity for re-routing traffic on failure In case of single failure the network traffic is spread across network backup links The LSPs are created independently, specifying different paths that are based on user-defined policies

17 Traffic Engineering

18 Resource Reservation Protocol with Traffic Engineering Extensions (RSVP-TE) Request bandwidth and traffic conditions on a defined path Uses two types of massages: RSVP PATH msg and RSVP RESERVATION msg Calculates best path based on the specified constraints TE interface parameters: Maximum Bandwidth Maximum Reservable Bandwidth Unreserved Bandwidth TE Metric (given by IGP protocol) Administrative Group (Link Affinity or “Link Coloring”) Drawback: Requires regular refreshes Scalability

19 Resource Reservation Protocol with Traffic Engineering Extensions (RSVP-TE)

20 Benefits from MPLS MPLS combines the performance characteristics of layer 2 networks and the connectivity and network services of layer 3 networks Combines IP and ATM in the network Improves packet-forwarding performance in the network Supports network scalability Improves the possibilities for traffic engineering Supports the delivery of services with QoS guarantees

21 Thank You! w