MPLS, THE BASICS CSE 6067, UIU. Multiprotocol Label Switching

Transcription

1 MPLS, THE BASICS CSE 6067, UIU Multiprotocol Label Switching

2 Basic Concepts of MPLS 2 Contents Drawbacks of Traditional IP Forwarding Basic MPLS Concepts MPLS versus IP over ATM Traffic Engineering with MPLS MPLS Architecture MPLS Labels Label Switch Routers

3 Drawbacks of Traditional IP Forwarding 3 Routing protocols are used to distribute Layer 3 routing information. Forwarding is based on the destination address only. Routing lookups are performed on every hop.

4 Drawbacks of Traditional IP Forwarding (Cont.) Traditional IP Forwarding 4 Every router may need full Internet routing information (more than 100,000 routes).

5 Drawbacks of Traditional IP Forwarding (Cont.) Traditional IP Forwarding 5 Every router may need full Internet routing information (more than 100,000 routes). Destination-based routing lookup is needed on every hop.

6 Drawbacks of Traditional IP Forwarding (Cont.) IP over ATM 6 Layer 2 devices have no knowledge of Layer 3 routing information virtual circuits must be manually established.

7 Drawbacks of Traditional IP Forwarding (Cont.) IP over ATM 7 Layer 2 devices have no knowledge of Layer 3 routing information virtual circuits must be manually established. Layer 2 topology may be different from Layer 3 topology, resulting in suboptimal paths and link use. Even if the two United topologies International University overlap, (UIU) the hub-and-

8 Drawbacks of Traditional IP Forwarding (Cont.) Traffic Engineering 8 Most traffic goes between large sites A and B, and uses only the primary link. Destination-based routing does not provide any mechanism for load balancing across unequal paths. Policy-based routing can be used to forward packets based on other parameters, but this is not a scalable solution.

9 Basic MPLS Concepts 9 MPLS is a new forwarding mechanism in which packets are forwarded based on labels. Labels usually correspond to IP destination networks (equal to traditional IP forwarding). Labels can also correspond to other parameters, such as QoS or source address. MPLS was designed to support forwarding of other protocols as well.

10 Basic MPLS Concepts (Cont.) 10 Example

11 Basic MPLS Concepts (Cont.) 11 Example Only edge routers must perform a routing lookup.

12

13 MPLS versus IP over ATM 13 Layer 2 devices are IP-aware and run a routing protocol.

14 MPLS Versus IP over ATM 14 Layer 2 devices are IP-aware and run a routing protocol. There is no need to manually establish virtual circuits.

15 MPLS Versus IP over ATM 15 Layer 2 devices are IP-aware and run a routing protocol. There is no need to manually establish virtual circuits. MPLS provides a virtual full-mesh topology.

16 Traffic Engineering with MPLS 16 Traffic can be forwarded based on other parameters (QoS, source,...). Load sharing across unequal paths can be achieved.

17 MPLS Architecture 17 MPLS has two major components: Control plane: Exchanges Layer 3 routing information and labels Data plane: Forwards packets based on labels Control plane contains complex mechanisms to exchange routing information, such as OSPF, EIGRP, IS-IS, and BGP, and to exchange labels, such as TDP, LDP, BGP, and RSVP. Data plane has a simple forwarding engine.

18 MPLS Architecture (Cont.) 18 Router functionality is divided into two major parts: control plane and data plane

19 MPLS Architecture (Cont.) 19 Router functionality is divided into two major parts: control plane and data plane

20 MPLS Architecture (Cont.) 20 Router functionality is divided into two major parts: control plane and data plane

21 MPLS Architecture (Cont.) 21 Router functionality is divided into two major parts: control plane and data plane

22 MPLS Architecture (Cont.) 22 Router functionality is divided into two major parts: control plane and data plane

23 MPLS Labels 23 MPLS technology is intended to be used anywhere regardless of Layer 1 media and Layer 2 protocol. MPLS uses a 32-bit label field that is inserted between Layer 2 and Layer 3 headers

24 MPLS Labels (Cont.) 24 Label Format MPLS uses a 32-bit label field that contains the following information: 20-bit label 3-bit experimental field 1-bit bottom-of-stack indicator 8-bit TTL field

25 MPLS Label Stack 25 Protocol identifier in a Layer 2 header specifies that the payload starts with a label (labels) and is followed by an IP header. Bottom-of-stack bit indicates whether the next header is another label or a Layer 3 header. Receiving router uses the top label only.

26 MPLS Label Stack (Cont.) 26 Usually only one label is assigned to a packet. The following scenarios may produce more than one label: MPLS VPNs (two labels: The top label points to the egress router and the second label identifies the VPN.) MPLS TE (two or more labels: The top label points to the endpoint of the traffic engineering tunnel and the second label points to the destination.)

27 MPLS Labels (Cont.) 27

28 MPLS Labels (Cont.) 28

29 Label Switch Routers 29 LSR primarily forwards labeled packets (label swapping). Edge LSR primarily labels IP packets and forwards them into the MPLS domain, or removes labels and forwards IP packets out of

30 Label Switch Routers (Cont.) 30 Architecture of LSRs LSRs, regardless of the type, perform these functions: Exchange routing information Exchange labels Forward packets The first two functions are part of the control plane. The last function is part of the data plane.

31 Label Switch Routers (Cont.) 31 Architecture of LSRs (Cont.)

32 Label Switch Routers (Cont.) 32 Architecture of Edge LSRs

33 Review 33 Drawbacks of Traditional IP Routing Basic MPLS Concepts MPLS Versus IP over ATM Traffic Engineering with MPLS MPLS Architecture MPLS Labels Label Switch Routers

34 Additional Queries 34 For further assistance, please mail at