© 2006 Cisco Systems, Inc. All rights reserved.ISCW v1.03-1 Implementation of Frame Mode MPLS Introducing MPLS Networks. - презентация

1 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v Implementation of Frame Mode MPLS Introducing MPLS Networks

2 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v The MPLS Conceptual Model

3 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v VPN Topologies

4 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v Basic MPLS Features MPLS is a switching 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: –Layer 3 VPN destination –Layer 2 circuit –Outgoing interface on the egress router –QoS –Source address MPLS was designed to support forwarding of non-IP protocols as well.

5 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v Basic MPLS Concepts Example Only edge routers must perform a routing lookup. Core routers switch packets based on simple label lookups and swap labels.

6 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v Router Switching Mechanisms

7 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v Cisco IOS Platform Switching Mechanisms The Cisco IOS platform supports three IP switching mechanisms: Routing table-driven switchingprocess switching: –Full lookup is performed at every packet Cache-driven switchingfast switching: –Most recent destinations are entered in the cache –First packet is always process-switched Topology-driven switching: –CEF (prebuilt FIB table)

8 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v Standard IP Switching Review

9 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v CEF Switching Review

10 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v MPLS Architecture

11 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v Major Components of MPLS Architecture Control plane: –Exchanges routing information and labels –Contains complex mechanisms to exchange routing information, such as OSPF, EIGRP, IS-IS, and BGP –Exchanges labels, such as LDP, BGP, and RSVP Data plane: –Forwards packets based on labels –Has a simple forwarding engine

12 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v Control Plane Components Example Information from control plane is sent to data plane.

13 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v MPLS Labels

14 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v MPLS Labels 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 (frame mode MPLS). MPLS over ATM uses the ATM header as the label (cell mode MPLS).

15 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v Label Format MPLS uses a 32-bit label field that contains this information: 20-bit label 3-bit experimental field 1-bit bottom-of-stack indicator 8-bit TTL field

16 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v Label Stack Protocol ID (PID) in a Layer 2 header specifies that the payload starts with a label (or 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.

17 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v Frame Mode MPLS

18 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v Label Switch Routers

19 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v Label Switch Routers LSR primarily forwards labeled packets (swap label). Edge LSR: –Labels IP packets (impose label) and forwards them into the MPLS domain –Removes labels (pop label) and forwards IP packets out of the MPLS domain

20 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v LSR Component Architecture

21 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v Functions of LSRs ComponentFunctions Control planeExchanges routing information Exchanges labels Data planeForwards packets (LSRs and edge LSRs)

22 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v Component Architecture of LSR

23 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v Component Architecture of Edge LSR

24 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v Summary MPLS is a switching mechanism that uses labels to forward packets. The result of using labels is that only edge routers perform a routing lookup; all the core routers simply forward packets based on labels assigned at the edge. MPLS consists of two major components: control plane and data plane. MPLS uses a 32-bit label field that contains label, experimental field, bottom-of-stack indicator, and TTL field. LSR is a device that forwards packets primarily based on labels. Edge LSR is a device that labels packets or removes labels from packets. Exchange routing information and exchange labels are part of the control plane, while forward packets is part of the data plane.

25 © 2006 Cisco Systems, Inc. All rights reserved.ISCW v