This document provides an introduction to MPLS (Multi-Protocol Label Switching). It discusses some of the limitations of traditional IP routing and forwarding and how MPLS aims to address these. MPLS uses label switching to establish label switched paths (LSPs) across networks in a way that is independent of the underlying link layer and network layer protocols. Key aspects of MPLS covered include label distribution protocols, traffic engineering capabilities, and explicit routing.
This document provides an introduction and overview of MPLS (Multi-Protocol Label Switching). It defines MPLS, discusses why it was developed to address limitations in IP routing, and how it works by assigning labels to packets which are then forwarded based on the label rather than long IP address lookups. Key MPLS concepts covered include label edge routers, label switch routers, label switch paths, and protocols like LDP and RSVP-TE. Applications like traffic engineering and MPLS VPNs are also mentioned.
Overview of the MPLS backbone transmission technology.
MPLS (MultiProtocol Layer Switching) is a layer 2.5 technology that combines the virtues of IP routing and fast layer 2 packet switching.
IP packet forwarding is not suited for high-speed forwarding due to the need to evaluate multiple routes for each IP packet in order to find the optimal route, i.e. the route with the longest prefix match.
However, Internet Protocol routing provides global reachability through the IP address and through IP routing protocols like BGP or OSPF.
Layer 2 packet switching has complementary characteristics in that it does not provide global reachability through globally unique addresses but allows fast packet forwarding in hardware through the use of small and direct layer 2 lookup addresses.
MPLS combines IP routing and layer 2 switching by establishing layer 2 forwarding paths based on routes received through IP routing protocols like BGP or OSPF.
Thus the control plane of an MPLS capable device establishes layer 2 forwarding paths while the data plane then performs packet forwarding, often in hardware.
MPLS is not a layer 2 technology itself, i.e. it does not define a layer 2 protocol but rather makes use of existing layer 2 technologies like Ethernet, ATM or Frame Relay.
Tutorial about MPLS Implementation with Cisco Router, this first of two chapter discuss about What is MPLS, Network Design, P, PE, and CE Router Description, Case Study of IP MPLS Implementation, IP and OSPF Routing Configuration
MPLS is a technology that allows traffic to be forwarded through networks based on short fixed length labels rather than long network addresses, enabling traffic engineering and quality of service. It works by classifying packets into forwarding equivalency classes, assigning labels when packets enter the MPLS domain, and using label switching to forward packets along label switched paths. MPLS provides advantages like simplified packet forwarding, efficient traffic engineering capabilities, and virtual private networks.
This document provides an overview of Multi-Protocol Label Switching (MPLS) technology. It discusses MPLS fundamentals, components, operations, applications for traffic engineering, virtual private networks, and any transport over MPLS. It also outlines topics like MPLS label distribution, virtual private network models, and future developments in MPLS. The document is intended to guide readers on key concepts in MPLS and provide background for further study.
This document provides an overview of MPLS basics:
- MPLS integrates Layer 2 switching and Layer 3 routing to satisfy networking requirements for various applications. It groups packets into forwarding equivalence classes (FECs) and assigns each FEC a label.
- Label switching routers (LSRs) establish label switched paths (LSPs) to forward labeled packets hop-by-hop through the MPLS network. The ingress LER labels incoming packets and the egress LER removes labels before forwarding.
- MPLS supports technologies like VPNs and traffic engineering to provide benefits like address multiplexing, QoS, and traffic control capabilities.
An introduction to MPLS networks and applicationsShawn Zandi
Multiprotocol Label Switching (MPLS) provides label switched path to deliver packets in networks. This is an introduction course to understand different terminologies and concepts associated with MPLS.
This document provides an introduction and overview of MPLS (Multi-Protocol Label Switching). It defines MPLS, discusses why it was developed to address limitations in IP routing, and how it works by assigning labels to packets which are then forwarded based on the label rather than long IP address lookups. Key MPLS concepts covered include label edge routers, label switch routers, label switch paths, and protocols like LDP and RSVP-TE. Applications like traffic engineering and MPLS VPNs are also mentioned.
Overview of the MPLS backbone transmission technology.
MPLS (MultiProtocol Layer Switching) is a layer 2.5 technology that combines the virtues of IP routing and fast layer 2 packet switching.
IP packet forwarding is not suited for high-speed forwarding due to the need to evaluate multiple routes for each IP packet in order to find the optimal route, i.e. the route with the longest prefix match.
However, Internet Protocol routing provides global reachability through the IP address and through IP routing protocols like BGP or OSPF.
Layer 2 packet switching has complementary characteristics in that it does not provide global reachability through globally unique addresses but allows fast packet forwarding in hardware through the use of small and direct layer 2 lookup addresses.
MPLS combines IP routing and layer 2 switching by establishing layer 2 forwarding paths based on routes received through IP routing protocols like BGP or OSPF.
Thus the control plane of an MPLS capable device establishes layer 2 forwarding paths while the data plane then performs packet forwarding, often in hardware.
MPLS is not a layer 2 technology itself, i.e. it does not define a layer 2 protocol but rather makes use of existing layer 2 technologies like Ethernet, ATM or Frame Relay.
Tutorial about MPLS Implementation with Cisco Router, this first of two chapter discuss about What is MPLS, Network Design, P, PE, and CE Router Description, Case Study of IP MPLS Implementation, IP and OSPF Routing Configuration
MPLS is a technology that allows traffic to be forwarded through networks based on short fixed length labels rather than long network addresses, enabling traffic engineering and quality of service. It works by classifying packets into forwarding equivalency classes, assigning labels when packets enter the MPLS domain, and using label switching to forward packets along label switched paths. MPLS provides advantages like simplified packet forwarding, efficient traffic engineering capabilities, and virtual private networks.
This document provides an overview of Multi-Protocol Label Switching (MPLS) technology. It discusses MPLS fundamentals, components, operations, applications for traffic engineering, virtual private networks, and any transport over MPLS. It also outlines topics like MPLS label distribution, virtual private network models, and future developments in MPLS. The document is intended to guide readers on key concepts in MPLS and provide background for further study.
This document provides an overview of MPLS basics:
- MPLS integrates Layer 2 switching and Layer 3 routing to satisfy networking requirements for various applications. It groups packets into forwarding equivalence classes (FECs) and assigns each FEC a label.
- Label switching routers (LSRs) establish label switched paths (LSPs) to forward labeled packets hop-by-hop through the MPLS network. The ingress LER labels incoming packets and the egress LER removes labels before forwarding.
- MPLS supports technologies like VPNs and traffic engineering to provide benefits like address multiplexing, QoS, and traffic control capabilities.
An introduction to MPLS networks and applicationsShawn Zandi
Multiprotocol Label Switching (MPLS) provides label switched path to deliver packets in networks. This is an introduction course to understand different terminologies and concepts associated with MPLS.
This document provides an overview of MPLS (Multi-Protocol Label Switching). It discusses the basic idea behind MPLS, the history and components. MPLS assigns labels to IP flows to create label switched paths between ingress and egress routers. Routers forward packets based on lookups of these labels rather than long IP addresses. MPLS supports traffic engineering and quality of service across networks while integrating technologies like IP, ATM, and Frame Relay.
This document provides an overview and introduction to MPLS (Multi-Protocol Label Switching). It defines key MPLS concepts such as label switching, forwarding equivalence classes, label switched paths, and label distribution protocols. It also describes how MPLS works, the benefits it provides including traffic engineering and virtual private networks, and examples of MPLS encapsulation over different link layer technologies like ATM, Frame Relay, and PPP/LAN networks.
- MPLS stands for Multi-Protocol Label Switching and was originally introduced to improve router forwarding speeds and meet bandwidth management requirements in IP networks.
- MPLS uses labels to forward packets based on their destination rather than long IP addresses. Label Edge Routers assign labels and interface with external networks, while Label Switch Routers in the core switch packets based on their labels.
- MPLS establishes Label Switched Paths between ingress and egress routers to efficiently route packets through the network based on forwarding tables that map incoming to outgoing labels. This allows traffic engineering and quality of service control.
LDP allows MPLS routers to exchange label mapping information by establishing LDP sessions between peers. LDP defines procedures and messages for routers to advertise label bindings and establish label switched paths for forwarding traffic. LDP sessions can be directly connected over a single hop or nondirectly connected over multiple hops using targeted Hellos.
MPLS is a forwarding scheme that uses fixed-length labels to simplify packet forwarding. It allows explicit routing and fast restoration from failures. MPLS headers carry labels that are used by routers to forward packets based on forwarding equivalence classes. This enables traffic management and quality of service routing. Local protection techniques like bypass tunnels and label stacking allow MPLS to provide fast restoration by pre-establishing backup label switched paths.
MPLS is a forwarding technique that uses fixed-length labels to make forwarding decisions instead of long variable-length IP addresses. MPLS inserts a label between the link layer and network layer headers. Routers along the path are known as label switching routers that use label values for forwarding instead of lookups in routing tables. MPLS supports quality of service and fast restoration upon failures by pre-establishing backup label switched paths.
Multi-Protocol Label Switching has become by far one of the most important Internet technologies of the last 15 years. From humble beginnings back in 1996-97, it is literally the defacto standard in a large majority of service provider networks today. This presentation, delivered to executives at MTNL, Mumbai (a large regional carrier in India), explains the key operational principles behind MPLS, and its significant applications.
- Multi-Protocol Label Switching (MPLS) improves forwarding speed and enables new capabilities like traffic engineering and virtual private networks. It uses short fixed-length labels to represent IP packets and make forwarding decisions.
- MPLS was originally conceived as being independent of Layer 2 but has found success deploying IP networks across ATM backbones. Standards are being developed and it is seen as an important network development.
- MPLS encapsulates IP packets with labels which are then used instead of the IP header for forwarding decisions, allowing separation of the forwarding and control planes.
Tutorial about MPLS Implementation with Cisco Router, this second of two chapter discuss about MPLS Configuration, LDP Configuration, VPN Services, L2VPN (VLL & VPLS) and L3VPN (VPRN).
it also contain case study and implementation of VLL, VPLS, and VPRN
MPLS is a forwarding scheme designed to speed up IP packet forwarding by using fixed length labels in packet headers to determine forwarding instead of long IP addresses. MPLS provides fast failure restoration through approaches like local protection which uses label stacking to allow a single bypass tunnel to protect multiple primary label switched paths (LSPs). Frame Relay is a public WAN technology based on packet switching that establishes virtual circuits between user ports to transport variable length data frames. It offers advantages over leased lines like more efficient use of bandwidth and topology flexibility but does not guarantee frame delivery. Asynchronous Transfer Mode (ATM) is a cell switching standard using small fixed size packets to efficiently multiplex different types of digital traffic like voice, data and images.
MPLS stands for Multi-Protocol Label Switching, a framework specified by the IETF to efficiently forward, route, and switch traffic through a network. MPLS works at layer 2.5, using label switching to combine the benefits of circuit switching and packet switching. It allows separation of addressing and traffic through VPNs, improving security, bandwidth utilization, and user experience while reducing network complexity and congestion.
MPLS is a forwarding mechanism that uses labels instead of IP addresses to forward packets. It allows routers to forward based on simple label lookups rather than complex routing lookups. MPLS has benefits like supporting multiple applications and decreasing forwarding overhead on core routers. It has a control plane that exchanges routing information and labels, and a data plane that forwards packets based on labels. Label Switch Routers implement MPLS forwarding by exchanging labels and forwarding packets based on those labels.
The document discusses performance measurements of MPLS traffic engineering and QoS. It provides background on traditional IP routing and its disadvantages, and explains the need for MPLS to address issues like traffic engineering, QoS, and scalability. Key MPLS concepts covered include FEC, LER, LSR, LSP, labels, label switching, label stacking, LIB tables, and the forwarding process. Traditional IP routing is compared to MPLS forwarding.
“MPLS is that it’s a technique, not a service.”
The fundamental concept behind MPLS is that of labeling packets. In a traditional routed IP network,
each router makes an independent forwarding decision for each packet based solely on the packet’s
network-layer header. Thus, every time a packet arrives at a router, the router has to “think through”
where to send the packet next.
It is considered to be the most perfect solution to address the most recently faced problems in present-day networks such as
“Routing, scalability, quality of service engineering management, traffic engineering”
This document provides an overview and student guide for the "Implementing Cisco MPLS (MPLS) Version 2.2" course. It introduces basic MPLS concepts including the MPLS architecture, labels, label stacks, and applications such as MPLS VPNs and traffic engineering. It also covers frame-mode MPLS implementation on Cisco IOS platforms, including configuration, monitoring, and troubleshooting tasks. Finally, it discusses MPLS VPN technology in depth, including the MPLS VPN architecture, routing model, and packet forwarding mechanisms.
The document provides information about a training event on Deploy MPLS Traffic Engineering taking place from 20 February to 2 March 2017 in Ho Chi Minh City, Vietnam. It includes details about two presenters - Nurul Islam Roman, Manager of Training & Technical Assistance at APNIC, and Jessica Wei, Training Officer at APNIC. It also acknowledges Cisco Systems and provides an agenda with topics on why MPLS Traffic Engineering is used and how it works.
This document provides an overview of MPLS (Multi-Protocol Label Switching) including its motivation, basics, components, operation, and advantages/disadvantages. MPLS was created to combine the fast packet forwarding of ATM with the flexibility of IP by using labels to direct network traffic. Key components include label edge routers that apply/remove labels, label switching routers that forward based on labels, label distribution protocols to disseminate label mappings, and label switched paths that represent forwarding equivalency classes. MPLS allows for traffic engineering, quality of service, and network scalability.
The document provides an overview of MPLS (Multi-Protocol Label Switching) concepts and components. It discusses how MPLS separates routing from forwarding by using labels to forward packets based on the label rather than the IP address. It describes MPLS components like edge label switching routers (ELSR or PE), label switching routers (LSR or P), and the label distribution protocol (LDP). It also provides examples of MPLS forwarding and MPLS VPN operation.
The document provides an introduction to MPLS (Multi-Protocol Label Switching) covering its definition, advantages, architecture, labels, label switching path setup, and forwarding operations. Key points include:
- MPLS encapsulates packets with short fixed-length labels to enable faster forwarding based on the label rather than the IP address.
- MPLS decouples routing from forwarding and supports traffic engineering and virtual private networks.
- The MPLS architecture consists of label edge routers, label switch routers, label distribution protocols, and label forwarding tables.
- Labels are assigned and distributed to establish label switched paths for forwarding packets across the MPLS network.
MPLS provides benefits such as supporting multiple applications, decreasing forwarding overhead on core routers, and supporting forwarding of non-IP protocols. MPLS establishes label switched paths using label distribution protocols like LDP to propagate labels between routers so that packets can be forwarded based on a label lookup rather than a routing table lookup at every hop. During convergence after a link failure, routing protocols first reconverge while MPLS convergence involves repopulating forwarding information based on stored label mappings.
This document provides an overview of MPLS (Multi-Protocol Label Switching). It discusses the basic idea behind MPLS, the history and components. MPLS assigns labels to IP flows to create label switched paths between ingress and egress routers. Routers forward packets based on lookups of these labels rather than long IP addresses. MPLS supports traffic engineering and quality of service across networks while integrating technologies like IP, ATM, and Frame Relay.
This document provides an overview and introduction to MPLS (Multi-Protocol Label Switching). It defines key MPLS concepts such as label switching, forwarding equivalence classes, label switched paths, and label distribution protocols. It also describes how MPLS works, the benefits it provides including traffic engineering and virtual private networks, and examples of MPLS encapsulation over different link layer technologies like ATM, Frame Relay, and PPP/LAN networks.
- MPLS stands for Multi-Protocol Label Switching and was originally introduced to improve router forwarding speeds and meet bandwidth management requirements in IP networks.
- MPLS uses labels to forward packets based on their destination rather than long IP addresses. Label Edge Routers assign labels and interface with external networks, while Label Switch Routers in the core switch packets based on their labels.
- MPLS establishes Label Switched Paths between ingress and egress routers to efficiently route packets through the network based on forwarding tables that map incoming to outgoing labels. This allows traffic engineering and quality of service control.
LDP allows MPLS routers to exchange label mapping information by establishing LDP sessions between peers. LDP defines procedures and messages for routers to advertise label bindings and establish label switched paths for forwarding traffic. LDP sessions can be directly connected over a single hop or nondirectly connected over multiple hops using targeted Hellos.
MPLS is a forwarding scheme that uses fixed-length labels to simplify packet forwarding. It allows explicit routing and fast restoration from failures. MPLS headers carry labels that are used by routers to forward packets based on forwarding equivalence classes. This enables traffic management and quality of service routing. Local protection techniques like bypass tunnels and label stacking allow MPLS to provide fast restoration by pre-establishing backup label switched paths.
MPLS is a forwarding technique that uses fixed-length labels to make forwarding decisions instead of long variable-length IP addresses. MPLS inserts a label between the link layer and network layer headers. Routers along the path are known as label switching routers that use label values for forwarding instead of lookups in routing tables. MPLS supports quality of service and fast restoration upon failures by pre-establishing backup label switched paths.
Multi-Protocol Label Switching has become by far one of the most important Internet technologies of the last 15 years. From humble beginnings back in 1996-97, it is literally the defacto standard in a large majority of service provider networks today. This presentation, delivered to executives at MTNL, Mumbai (a large regional carrier in India), explains the key operational principles behind MPLS, and its significant applications.
- Multi-Protocol Label Switching (MPLS) improves forwarding speed and enables new capabilities like traffic engineering and virtual private networks. It uses short fixed-length labels to represent IP packets and make forwarding decisions.
- MPLS was originally conceived as being independent of Layer 2 but has found success deploying IP networks across ATM backbones. Standards are being developed and it is seen as an important network development.
- MPLS encapsulates IP packets with labels which are then used instead of the IP header for forwarding decisions, allowing separation of the forwarding and control planes.
Tutorial about MPLS Implementation with Cisco Router, this second of two chapter discuss about MPLS Configuration, LDP Configuration, VPN Services, L2VPN (VLL & VPLS) and L3VPN (VPRN).
it also contain case study and implementation of VLL, VPLS, and VPRN
MPLS is a forwarding scheme designed to speed up IP packet forwarding by using fixed length labels in packet headers to determine forwarding instead of long IP addresses. MPLS provides fast failure restoration through approaches like local protection which uses label stacking to allow a single bypass tunnel to protect multiple primary label switched paths (LSPs). Frame Relay is a public WAN technology based on packet switching that establishes virtual circuits between user ports to transport variable length data frames. It offers advantages over leased lines like more efficient use of bandwidth and topology flexibility but does not guarantee frame delivery. Asynchronous Transfer Mode (ATM) is a cell switching standard using small fixed size packets to efficiently multiplex different types of digital traffic like voice, data and images.
MPLS stands for Multi-Protocol Label Switching, a framework specified by the IETF to efficiently forward, route, and switch traffic through a network. MPLS works at layer 2.5, using label switching to combine the benefits of circuit switching and packet switching. It allows separation of addressing and traffic through VPNs, improving security, bandwidth utilization, and user experience while reducing network complexity and congestion.
MPLS is a forwarding mechanism that uses labels instead of IP addresses to forward packets. It allows routers to forward based on simple label lookups rather than complex routing lookups. MPLS has benefits like supporting multiple applications and decreasing forwarding overhead on core routers. It has a control plane that exchanges routing information and labels, and a data plane that forwards packets based on labels. Label Switch Routers implement MPLS forwarding by exchanging labels and forwarding packets based on those labels.
The document discusses performance measurements of MPLS traffic engineering and QoS. It provides background on traditional IP routing and its disadvantages, and explains the need for MPLS to address issues like traffic engineering, QoS, and scalability. Key MPLS concepts covered include FEC, LER, LSR, LSP, labels, label switching, label stacking, LIB tables, and the forwarding process. Traditional IP routing is compared to MPLS forwarding.
“MPLS is that it’s a technique, not a service.”
The fundamental concept behind MPLS is that of labeling packets. In a traditional routed IP network,
each router makes an independent forwarding decision for each packet based solely on the packet’s
network-layer header. Thus, every time a packet arrives at a router, the router has to “think through”
where to send the packet next.
It is considered to be the most perfect solution to address the most recently faced problems in present-day networks such as
“Routing, scalability, quality of service engineering management, traffic engineering”
This document provides an overview and student guide for the "Implementing Cisco MPLS (MPLS) Version 2.2" course. It introduces basic MPLS concepts including the MPLS architecture, labels, label stacks, and applications such as MPLS VPNs and traffic engineering. It also covers frame-mode MPLS implementation on Cisco IOS platforms, including configuration, monitoring, and troubleshooting tasks. Finally, it discusses MPLS VPN technology in depth, including the MPLS VPN architecture, routing model, and packet forwarding mechanisms.
The document provides information about a training event on Deploy MPLS Traffic Engineering taking place from 20 February to 2 March 2017 in Ho Chi Minh City, Vietnam. It includes details about two presenters - Nurul Islam Roman, Manager of Training & Technical Assistance at APNIC, and Jessica Wei, Training Officer at APNIC. It also acknowledges Cisco Systems and provides an agenda with topics on why MPLS Traffic Engineering is used and how it works.
This document provides an overview of MPLS (Multi-Protocol Label Switching) including its motivation, basics, components, operation, and advantages/disadvantages. MPLS was created to combine the fast packet forwarding of ATM with the flexibility of IP by using labels to direct network traffic. Key components include label edge routers that apply/remove labels, label switching routers that forward based on labels, label distribution protocols to disseminate label mappings, and label switched paths that represent forwarding equivalency classes. MPLS allows for traffic engineering, quality of service, and network scalability.
The document provides an overview of MPLS (Multi-Protocol Label Switching) concepts and components. It discusses how MPLS separates routing from forwarding by using labels to forward packets based on the label rather than the IP address. It describes MPLS components like edge label switching routers (ELSR or PE), label switching routers (LSR or P), and the label distribution protocol (LDP). It also provides examples of MPLS forwarding and MPLS VPN operation.
The document provides an introduction to MPLS (Multi-Protocol Label Switching) covering its definition, advantages, architecture, labels, label switching path setup, and forwarding operations. Key points include:
- MPLS encapsulates packets with short fixed-length labels to enable faster forwarding based on the label rather than the IP address.
- MPLS decouples routing from forwarding and supports traffic engineering and virtual private networks.
- The MPLS architecture consists of label edge routers, label switch routers, label distribution protocols, and label forwarding tables.
- Labels are assigned and distributed to establish label switched paths for forwarding packets across the MPLS network.
MPLS provides benefits such as supporting multiple applications, decreasing forwarding overhead on core routers, and supporting forwarding of non-IP protocols. MPLS establishes label switched paths using label distribution protocols like LDP to propagate labels between routers so that packets can be forwarded based on a label lookup rather than a routing table lookup at every hop. During convergence after a link failure, routing protocols first reconverge while MPLS convergence involves repopulating forwarding information based on stored label mappings.
Multi-Protocol Label Switching (MPLS) allows packets to be forwarded along predetermined paths through a network based on short fixed-length labels rather than long variable-length IP addresses. MPLS is used by carriers and large enterprises to implement traffic engineering, virtual private networks, and quality of service through mechanisms like traffic classification and label switching along label switch paths.
Segment routing is a technology that is gaining popularity as a way to simplify MPLS networks. It has the benefits of interfacing with software-defined networks and allows for source-based routing. It does this without keeping state in the core of the network and needless to use LDP and RSVP-TE.
MPLS provides motivation to converge voice and data on a single network with increasing traffic demands. It works by assigning labels to packets based on forwarding equivalence classes. Labels are distributed through protocols like LDP and are used to forward packets along label switched paths through label swapping without deep packet inspection. MPLS enables features like traffic engineering, QoS, and virtual private networks.
Multi Protocol Label Switching. (by Rahil Reyaz)RAHIL REYAZ
MPLS was developed to address some of the disadvantages of IP and ATM routing. It works by assigning labels to packets at the edge of the network which are then used to forward packets across the core. This label switching allows for faster forwarding than IP routing. MPLS can be used to engineer traffic flows, provide virtual private networks, and transport various layer 2 protocols over an IP or MPLS backbone. While it adds complexity, MPLS improves performance and supports quality of service and network scalability.
MPLS (Multi-Protocol Label Switching) is introduced as a "Layer 2.5" protocol that sits between traditional Layer 2 and Layer 3 networking. It works by assigning labels to packets at ingress routers and using those labels for fast forwarding decisions without additional routing lookups at subsequent routers. This improves performance over traditional IP routing. MPLS also enables traffic engineering through protocols like RSVP-TE that allow reserving bandwidth on specific paths. Other key MPLS concepts covered are label switching, MPLS signaling protocols, label stacking, pseudowires, VPN services, and fast reroute for improved convergence during failures.
The document discusses MPLS (Multi-Protocol Label Switching) including traditional IP forwarding, IP over ATM, MPLS concepts, MPLS architecture, MPLS forwarding, MPLS applications, MPLS protocols, and forwarding equivalence classes. MPLS combines the advantages of connection-oriented forwarding with IP routing by assigning labels to packets and forwarding based on those labels rather than long IP addresses.
1. MPLS simplifies forwarding by introducing label switching which uses a forwarding table and label carried in each packet rather than conventional IP routing based on IP addresses.
2. MPLS establishes label switched paths between routers where each router along the path transmits the packet to the next router by means of a label. Edge routers analyze packets and assign an initial label.
3. The main benefits of MPLS include improved performance, scalability, and traffic engineering capabilities compared to conventional IP routing.
1. MPLS simplifies forwarding by introducing label switching which uses a forwarding table and label carried in each packet rather than conventional IP routing based on IP addresses.
2. MPLS establishes label switched paths between routers where each router along the path transmits the packet to the next router by means of a label. Edge routers analyze packets and assign an initial label.
3. The main benefits of MPLS include improved performance, scalability, and traffic engineering capabilities compared to conventional IP routing.
This document provides an overview of MPLS (Multi-Protocol Label Switching) including:
- MPLS uses labels assigned at the edge of the network to forward packets through the core instead of IP addresses.
- Label Distribution Protocol (LDP) establishes label mappings between adjacent routers to distribute labels.
- Labels are assigned to Forwarding Equivalence Classes (FECs) which define how packets are mapped to Label Switched Paths (LSPs).
This document provides an overview and tutorial on MPLS (Multi-Protocol Label Switching). It begins with an outline of topics to be covered, including label encapsulations, label distribution protocols, MPLS and ATM integration, and constraint-based routing with CR-LDP. It then delves into explanations of label substitution, MPLS terminology, forwarding equivalence classes, vanilla and explicit label switched paths, and MPLS encapsulation over different link layers like ATM, Frame Relay, and PPP/LAN. It also briefly discusses label distribution protocols and the IETF status. The document aims to explain the key concepts and mechanisms of MPLS.
MPLS is a packet forwarding technique that can carry any layer 3 protocol. It works by assigning labels to packets at the edge router. Subsequent routers use these labels to forward packets without looking at the layer 3 headers, making forwarding more efficient. MPLS provides benefits like traffic engineering, quality of service, and scalability compared to traditional IP routing. It works by assigning packets to forwarding equivalence classes, assigning labels to these classes, and using label switching to forward packets based on these labels rather than IP routing lookups.
This document provides an overview of MPLS (Multi-Protocol Label Switching) concepts including label switching, label allocation, and label forwarding. It discusses MPLS label structure, label encapsulation, label spaces, label forwarding entries, and label distribution protocols. The key topics covered are:
1) MPLS was developed to integrate connectionless IP networks with connection-oriented ATM networks for traffic engineering and QoS purposes. It works by encapsulating packets with labels and performing label switching instead of IP forwarding.
2) MPLS uses labels added to packet headers to forward packets. Label allocation can be downstream-on-demand or unsolicited. Label distribution protocols like LDP are used to establish label
The document discusses several key functions and design goals of the network layer in internet architecture. It covers routing algorithms like distance vector and link state routing, as well as routing protocols like RIP. It also provides an overview of the TCP/IP protocol stack and some of its core components like IP, ICMP, TCP and UDP.
This document provides an overview of MPLS (Multiprotocol Label Switching) including:
- MPLS uses labels instead of IP addresses to forward packets for benefits like decreased routing overhead and support for non-IP protocols.
- Key MPLS terminology includes label-switched routers that forward packets based on labels, edge routers that impose/remove labels, and label switched paths that define the path through the network.
- The MPLS control plane establishes label switched paths and the data plane uses forwarding based on pre-established labels for faster switching compared to IP routing.
This document provides an overview of MPLS (Multi-Protocol Label Switching) including:
1) It describes the need for MPLS arising from limitations in traditional IP forwarding and issues running one statmux technology over another.
2) It explains basic MPLS concepts like label switching, label distribution protocols, label edge and switch routers, label switching paths, and forwarding equivalence classes.
3) It outlines the basic working process of MPLS including label encapsulation, lookup, and processing functions like push, pop and swap.
MPLS enables packets to be forwarded based on labels rather than IP addresses. PE routers add labels to incoming packets and remove labels from outgoing packets. P routers swap or pop labels to forward packets. MPLS with L3 VPN allows private networks in different locations to communicate securely over a shared infrastructure by associating routes with virtual routing instances (VRFs) and advertising them using BGP. An example configuration shows VRF and BGP configuration, along with commands to view MPLS label bindings and packet forwarding information.
1. 1
An Introduction to
MPLS
Timothy G. Griffin
griffin@research.att.com
http://www.research.att.com/~griffin
November 21, 2002
Researc
h
2. 2
What’s all this talk about
MPLS?
• “MPLS is going to solve all of our problems”
• “MPLS is a solution in search of a problem”
• “MPLS is all about traffic engineering”
• “MPLS is what I wish on all of my competitors”
• “MPLS is all about virtual private networks”
• “MPLS solves network operations problems”
• “MPLS creates network operations problems”
• “MPLS is all about lowering operational costs”
• “MPLS is going to cost more than its worth”
• “MPLS is the natural next step in Internet evolution”
• “MPLS is too complicated to survive in the Internet”
But what is MPLS anyway?
3. 3
Goals of this Tutorial
• To understand MPLS from a purely
technical point of view
– avoid the hype
– avoid the cynicism
• To understand the broad technical
issues without getting lost in the
vast number of details
– the gains
– the costs
– the tradeoffs
4. 4
Keep in Mind
• MPLS is an emerging technology
• Many technical issues have not yet been resolved
• Interest and enthusiasm is not universal, but primarily
found in large providers (and their vendors)
• Standards are rapidly evolving
• Implementations are rapidly evolving
• Operational experience and expertise still very scarce
Expect interoperability problems and
feature availability problems for the
next few years
5. 5
Outline
• Why MPLS?
– Problems with current IP routing and
forwarding
– Complexity of overlay model
• What is MPLS?
– Label swapping
– Label distribution
– Constraint based routing
• What applications could exploit MPLS?
– Traffic Engineering
– Virtual Private Networks
• Both Layer 2 and Layer 3 VPNs
6. 6
IP forwarding paths are implemented with destination-based
next hop tables
R
R
R
A
B
C
D
R1
R2
R3
R4 R5
E
Dest. Nxt Hop
R4
R3
R3
R4
Direct
R4
Dest. Nxt Hop
A
B
C
D
E
default
R2
R2
Direct
R5
R5
R2
Dest. Nxt Hop
A
B
C
D
E
default
R1
Direct
R3
R1
R3
R1
Default to
upstream
router
A
B
C
D
E
default
7. 7
IP Forwarding Process
Forwarding Process
IP Forwarding Table
Router
1. Remove a packet
from an input
queue
3. Match packet’s
destination to
a table entry
2. Check for sanity,
decrement TTL
field
4. Place packet on
correct output
queue
If queues
get full, just
drop packets!
If queues
get full, just
drop packets!
8. 8
IP routing protocols assume all
forwarding is destination-based
A
B
C
The next-hop forwarding paradigm
does not allow router R to choose
a route to A based on who originated
the traffic, B or C.
R
The Fish
9. 9
IP forwarding tables are maintained by dynamic routing protocols
IP Forwarding TableOSPF
Domain
RIP
Domain
BGP
OS kernel
OSPF Process
OSPF Routing tables
RIP Process
RIP Routing tables
BGP Process
BGP Routing tables
10. 10
Shortest Path Routing: Link weights
tend to attract or repel all traffic
A
B
C
1 1
12
A
B
C
1
1
1
2
D
D
12. 12
Advantages of Overlay
Networks
• ATM and Frame Relay switches offer high
reliability and low cost
• Virtual circuits can be reengineered
without changing the layer 3 network
• Large degree of control over traffic
• Detailed per-circuit statistics
• Isolates layer 2 network management from
the details of higher layer services
13. 13
Problems with Overlay
Networks
• Often use proprietary protocols and
management tools
• Often requires “full meshing” of statically
provisioned virtual circuits
• ATM cell tax ---- about 20% of bandwidth
• If layer 3 is all IP, then the overlay model
seems overly complicated and costly
• Advances in optical networking cast some
doubt on the entire approach
Overlay model is just fine when layer 2 network provides
diverse non IP services.
14. 14
Blur Layer 2 and 3?
router
switch
(ATM, Frame)
what is it?
this is not a router
this is not a switch
15. 15
Sanity Check?
• The problems with IP forwarding and
routing do not require technologies like
MPLS
– Many can be addressed with simple solutions.
Like the design of simple networks!
– The problems are not “show stoppers”
– The MPLS cure will have side effects
– For many applications, TCP/IP handles
congestion very well
• Technologies like MPLS may be very
valuable if they can enable new services
and generate new revenue
16. 16
Sign of the Times:
New Sub-IP area in the
IETF
• Multiprotocol Label Switching (mpls)
• Common Control and Management Protocols (ccamp)
• Internet Traffic Engineering (tewg)
• Provider Provisioned Virtual Private Networks (ppvpn)
• IP over Optics (ipo)
• IP over Resilient Packet Rings (iporpr)
• General Switch Management Protocol (gsmp)
See http://www.ietf.org/html.charters/foo-charter.html,
where foo is the working group acronym.
17. 17
MPLS = MultiProtocol Label Switching
Physical
Data Link
MPLS
Network
• A “Layer 2.5” tunneling protocol
• Based on ATM-like notion of
“label swapping”
• A simple way of labeling each
network layer packet
• Independent of Link Layer
• Independent of Network Layer
• Used to set up “Label-switched
paths” (LSP), similar to ATM
PVCs
RFC 3031 : Multiprotocol Label Switching Architecture
22. 22
A Label Switched Path (LSP)
417 data 666 data 233 data datadata
POP! PUSH!SWAP! SWAP!
A label switched path
“tail end” “head end”
Often called an MPLS tunnel: payload headers are not
Inspected inside of an LSP. Payload could be MPLS …
23. 23
Label Switched Routers
The data plane
IPIP Forwarding Table
IP inIP out
IP
Label Swapping Table
MPLS inMPLS out
77 data 23 data
represents IP Lookup + label push
represents label pop + IP lookup
24. 24
Forwarding Equivalence Class
(FEC)
417 IP1 666 IP1 IP1IP1
IP2 IP2
233 IP1
417 IP2 233 IP2666 IP2
Packets IP1 and IP2 are forwarded in the
same way --- they are in the same FEC.
Network layer headers are not inspected inside
an MPLS LSP. This means that inside of the tunnel
the LSRs do not need full IP forwarding table.
26. 26
Penultimate Hop Popping
417 IP 666 IP 233 IP IPIP
POP
+
IP Lookup
PUSHSWAP SWAP
666 IP 233 IP IPIP
IP Lookup PUSHPOP SWAP
IP
27. 27
LSP Hierarchy via Label Stacking
23 IP1
PUSH
IP1
23 IP1
POP
IP1
IP2 IP2
PUSHPOP
23 IP11723 IP18823 IP144
66 IP217
66 IP2
66 IP2
66 IP28866 IP244
Did I get carried away on this slide?
28. 28
MPLS Tunnels come at a
cost
• ICMP messages may be generated in the
middle of a tunnel, but the source
address of the “bad packet” may not be
in the IP forwarding table of the LSR!
– TTL expired: traceroute depends on this!
– MTU exceeded: Path MTU Discovery
(RFC1191) depends on this!
None of the proposed solutions are
without their own problems…
30. 30
But Native Labels May
Cause Big Headaches
• No TTL!
– Loop detection?
– Loop prevention?
• LSP merge may not be supported
– Label bindings cannot flow from
destination to source, but must be
requested at source
MPLS was initially designed to exploit the existence
of ATM hardware and reduce the complexity of overlay networks.
But IP/MPLS with native ATM labels results in a large number
of problems and complications.
31. 31
Basic MPLS Control Plane
MPLS control plane
=
IP control plane
+
label distribution
Label distribution protocols are needed to
(1) create label FEC bindings
(2) distribute bindings to neighbors,
(3) maintain consistent label swapping
tables
32. 32
Label Distribution:
Option I
“Piggyback” label information on top
of existing IP routing protocol
• Guarantees consistency of IP forwarding tables
and MPLS label swapping tables
• No “new” protocol required
• Allows only traditional destination-based, hop-by-
hop forwarding paths
• Some IP routing protocols are not suitable
• Need explicit binding of label to FEC
• Link state protocols (OSPF, ISIS) are implicit,
and so are not good piggyback candidates
• Distance vector (RIP) and path vector (BGP) are
good candidates. Example: BGP+
Good
Points
Bad
Points
33. 33
Label Distribution:
Option II
Create new label distribution protocol(s)
• Compatible with “Link State” routing protocols
• Not limited to destination-based, hop-by-hop
forwarding paths
• Additional complexity of new protocol and
interactions with existing protocols
• Transient inconsistencies between IP forwarding
tables and MPLS label swapping tables
Good
Points
Bad
Points
Examples: LDP (IETF) and TDP (Cisco proprietary)
34. 34
The Control Plane
IPIP Forwarding Table
IP inIP out
IP
Label Swapping Table
MPLS inMPLS out
77 data 23 data
IP Routing Protocols
+
IP Routing Tables
Label distribution protocols
+
Label Binding Tables
Routing messages
Label distribution
messages
35. 35
Label Distribution with BGP
Carrying Label Information in BGP-4
draft-ietf-mpls-bgp4-05.txt (1/2001)
Associates a label (or label stack)
with the BGP next hop.
Uses multiprotocol features of BGP:
RFC 2283. Multiprotocol Extensions for BGP-4
So routes with labels are in a different
address space than a vanilla routes (no labels)
36. 36
BGP piggyback not required for
simple iBGP optimization
417 IP 666 IP IPIP 233 IP
AS 888AS 444
BGP route Internal BGP
Map traffic to the LSP that
terminates at the egress router
chosen by BGP
A B
Routers A and B do not need full routing tables.
They only need IGP routes (and label bindings).
37. 37
BGP piggyback allows Interdomain
LSPs
IP
AS 888AS 444
BGP route
With label 99 Internal BGP with label 99
Use top of stack to get to
egress router, bottom of stack
for LSP in AS 444.
IP99 233 IP99666 IP99417 IP99
38. 38
MPLS tunnels can decrease
size of core routing state
• Core routers need only IGP routes and LSPs for IGP
routes
• Implies less route oscillation
• Implies less memory
• Implies less CPU usage
BUT: still need route reflectors to avoid full mesh
and/or to reduce BGP table size at border routers
BUT: since your core routers do not have full tables
you now have all of the MPLS problems associated with
ICMP source unknown (TTL, MTU, traceroute …)
Are these
really
problems?
39. 39
Label Distribution Protocol (LDP)
RFC 3036. LDP Specification. (1/2001)
• Dynamic distribution of label binding information
• Supports only vanilla IP hop-by-hop paths
• LSR discovery
• Reliable transport with TCP
• Incremental maintenance of label swapping
tables (only deltas are exchanged)
• Designed to be extensible with Type-Length-
Value (TLV) coding of messages
• Modes of behavior that are negotiated during
session initialization
• Label retention (liberal or conservative)
• LSP control (ordered or independent)
• Label assignment (unsolicited or on-demand)
40. 40
LDP Message Categories
• Discovery messages: used to announce and
maintain the presence of an LSR in a
network.
• Session messages: used to establish,
maintain, and terminate sessions between
LDP peers.
• Advertisement messages: used to create,
change, and delete label mappings for FECs.
• Notification messages: used to provide
advisory information and to signal error
information.
41. 41
LDP and Hop-by-Hop routing
417 IP 666 IP IPIP 233 IP
LSP
10.11.12.0/24
A B C D
417
10.11.12.0/24
LDP LDP LDP666 233
10.11.12.0/2410.11.12.0/24
10.11.12.0/24
next-hopnetwork
direct 10.11.12.0/24
next-hopnetwork
A 10.11.12.0/24
next-hopnetwork
B 10.11.12.0/24
next-hopnetwork
C
Generate new label
And bind to destination
pop swap swap push
DCBA
42. 42
MPLS Traffic Engineering
“A major goal of Internet Traffic
Engineering is to facilitate efficient and reliable
network operations while simultaneously optimizing
network resource utilization and performance.”
RFC 2702
Requirements for Traffic Engineering over MPLS
Intra-Domain
A Framework for Internet Traffic Engineering
Draft-ietf-tewg-framework-02.txt
Intra-Domain
“The optimization goals of traffic engineering are
To enhance the performance of IP traffic while utilizing
Network resources economically and reliably.”
43. 43
TE May Require Going
Beyond Hop-by-Hop
Routing
• Explicit routes
– Allow traffic sources to set up paths
• Constraint based routing
– Chose only best paths that do no violate
some constraints
– Needs explicit routing
– May need resource reservation
• Traffic classification
– Map traffic to appropriate LSPs
44. 44
Hop-by-Hop vs. Explicit
Routes
• Distributed
control
• Trees rooted at
destination
• Destination
based forwarding
• Originates at
source
• Paths from sources
to destinations
• Traffic to path
mapping based on
what configuration
commands your
vendor(s) provide
45. 45
Explicit path Setup
417 IP 666 IP IPIP 233 IP
LSP
A B C D
417
LSPID 17
reply 666 233
pop swap swap push
REQUEST
LSPID 17
Request
path
D->C->B->A
with LSPID 17
LSPID 17LSPID 17
replyreply
REQUEST
LSPID 17
REQUEST
LSPID 17
46. 46
Constraint Based Routing
1. Specify path constraints
2. Extend topology database to include
resource and constraint information
3. Find paths that do not violate
constraints and optimize some metric
4. Signal to reserve resources along path
5. Set up LSP along path (with explicit
route)
6. Map ingress traffic to the appropriate
LSPs
Basic components
Extend Link State
Protocols (IS-IS, OSPF)
Extend RSVP or LDP
or both!
Problem here: OSPF
areas hide information
for scalability. So these
extensions work best only
within an area…
Problem here: what is
the “correct” resource
model for IP services?Note: (3) could be offline,
or online (perhaps an extension to OSPF)
47. 47
Resource Reservation + Label
Distribution
Two emerging/competing/dueling approaches:
RSVP
+ +
LDP
CR-LDPRSVP-TE
Add label
distribution
and explicit
routes
to a resource
reservation
protocol
Add explicit
routes and resource
reservation to a
label distribution
protocol
Constraint-Based LSP Setup using LDP
draft-ietf-mpls-cr-lpd-05.txt
RSVP-TE: Extensions to RSVP for LSP Tunnels
draft-ietf-mpls-rsvp-lsp-tunnel-08.txt
48. 48
RSVP-TE vs. CR-LPD
• Soft state periodically
refreshed
• IntServe QoS model
• State maintained
incrementally
• New QoS model
derived from ATM
and Frame Relay
RSVP-TE
CR-LDP
And the QoS model determines the additional information
attached to links and nodes and distributed with extended
link state protocols…
And what about that other Internet QoS model, diffserve?
49. 49
A closer look at CR-LDP
• Defines new TLV encodings and procedures for
– Explicit routing (strict and loose)
– Route pinning (nail down some segments of a loosely
routed path)
– Traffic parameter specification
• Peak rate
• Committed rate
• Weight
• Resource class or color
– LSP preemption (reroute existing paths to
accommodate a new path)
– LSP Identifiers (LSPIDs)
51. 51
Use Shortest Paths to get beyond
Shortest Paths!
A
B
DCLPS
Vanilla IP
forwarding
The IP routing protocol at LSR
A is configured to (privately) see A -> C LSP
as one link with weight 1.
2
1
2
1
1
52. 52
MPLS TE: Is it worth the
cost?
• Much of the traffic across a (transit) ISPs
network is interdomain traffic
– Congestion is most common on peering links
– The current work on MPLS TE does not apply to
interdomain links! (Actually, it does not even work
well across OSPF areas…)
• MPLS TE is probably most valuable when IP
services require more than best effort
– VPNs with SLAs?
– Supporting differentiated services?
55. 55
Why Not Use MPLS
Tunnels?
C
Customer’s
Layer 3 VPN
A
C
B
A
B
C
Provider’s MPLS enabled network
MPLS LSP
MPLS LSP
MPLS LSP
56. 56
Potential Advantages of
MPLS Layer 2 VPNs
• Provider needs only a single network infrastructure
to support public IP, and VPN services, traffic
engineered services, and differentiated services
• Additional routing burden on provider is bounded
• Clean separation of administrative responsibilities.
Service provider does MPLS connectivity, customer
does layer 3 connectivity
• Easy transition for customers currently using
traditional Layer 2 VPNs
57. 57
BGP/MPLS VPNs
• RFC 2547
• Is Peer Model of VPN (not Overlay)
• Also draft-rosen-rfc2547bis-02.txt
• Cisco configuration info :
– http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/
120newft/120t/120t5/vpn.htm
AT&T’s IPFR service is based on this RFC.
Note that the Model of this RFC could be
implemented without MPLS. See
BGP/IPsec VPN
<draft-declercq-bgp-ipsec-vpn-00.txt>
60. 60
VPN Address Overlap Means Vanilla
Forwarding Tables Can’t Work
Site 1
Site 3
Site 2 p1
p2
VPRN 2
p1
Dest. Nxt Hop
p1
p2
??
??
Provider
Site 4
p2
VPRN 1
61. 61
Vanilla forwarding tables are out
Site 1
Site 3
Site 2 VPRN 1 p1
p3
VPRN 2
p2
Dest. Nxt Hop
p1
p2
p3
s1
s2
s3
Provider
Violates isolation
Guarantee of
A VPN: site 1 can
Exchange traffic with
Site 2!
VPN Overlap Means Vanilla Forwarding
Tables Can’t Work
62. 62
RFC 2547 : Per site forwarding tables
Site 1
Site 3
Site 2 VPRN 1 p1
p3
VPRN 2
p2
Provider
Dest. Nxt Hop
p1
p3
s1
s3
Dest. Nxt Hop
p2 s2
Dest. Nxt Hop
p2 s2
Site 1 FT Site 3 FT
Site 2 FT
Called VRFs, for "VPN Routing and Forwarding" tables.
64. 64
RFC 2547 Summary
• Piggyback VPN information on BGP
• New address family
• New attributes for membership
• New Per-site forwarding tables (VRFs)
• Use MPLS Tunnels between PEs
• No need for VPN routes on backbone
LSRs, only on PEs
65. 65
Layer 2 VPNs vs. BGP/MPLS
VPNs
• Customer routing stays with
customer
• May allow an easier
transition for customers
currently using Frame/ATM
circuits
• Familiar paradigm
• Easier to extend to multiple
providers
• Customer routing is
“outsourced” to provider
• Transition may be
complicated if customer has
many extranets or multiple
providers
• New “peering” paradigm
• Not clear how multiple
provider will work (IMHO)
66. 66
Summary
• provides an efficient and scalable
tunneling mechanism
• provides an efficient and scalable
mechanism for extending IP routing with
explicit routes
MPLS is an interesting and potentially valuable
technology because it
67. 67
More info on MPLS
• MPLS working group
– http://www.ietf.org/html.charters/mpls-charter.html
• MPLS email list archive
– http://cell.onecall.net/cell-relay/archives/mpls/mpls.index.html
• MPLS Resource Center
– http://www.mplsrc.com
• Peter Ashwood-Smith’s NANOG Tutorial
– http://www.nanog.org/mtg-9910/mpls.html
• MPLS: Technology and Applications. By Bruce Davie and Yakov
Rekhter. Morgan Kaufmann. 2000.
• MPLS: Is it all it's cracked up to be? Talk by Pravin K. Johri
– http://buckaroo.mt.att.com/~pravin/docs/mpls.pdf
68. 68
More info on MPLS TE
• tewg working group
– http://www.ietf.org/html.charters/tewg-charter.html
• NANOG Tutorial by Jeff Doyle and Chris
Summers
– http://www.nanog.org/mtg-0006/mpls.html
• NANOG Tutorial by Robert Raszuk
– http://www.nanog.org/mtg-0002/robert.html
69. 69
More info on MPLS VPNs
• PPVPN working group
– http://www.ietf.org/html.charters/ppvpn-charter.html
• PPVPN Archive
– http://nbvpn.francetelecom.com
• NANOG Panel:Provider-Provisioned VPNs
– http://www.nanog.org/mtg-0102/jessica.html
• MPLS and VPN Architectures. By Ivan
Pepelnjak and Jim Guichard. Cisco Press. 2001
Editor's Notes
&lt;number&gt;
Please email me with comments on this course.
The web site contains these slides, course information, and interesting routing related links.
This is intended to be a one day course.
&lt;number&gt;
Assume tables populated by magic.
If we assume all forwarding tables are populated in a consistent way, then there is no real danger in confusing “end to end route” with a “next hop route.” Of course, the study of routing techniques explores ways to ensure that this is a safe assumption.
&lt;number&gt;
See RFC 1264 “Internet Engineering Task Force Internet Routing Protocol Standardization Criteria.” 1991
&lt;number&gt;
In an ATM overlay network, routers surround the edge of the ATM cloud. Each router communicates with every other router by a set of PVCs that are configured across the ATM physical topology. The PVCs function as logical circuits, providing connectivity between edge routers. The routers do not have direct access to information describing the physical topology of the underlying ATM infrastructure. The routers have knowledge only of the individual PVCs that appear to them as simple point-to-point circuits between two routers. The illustration above shows how the physical topology of an ATM core differs from the logical IP overlay topology.
The distinct ATM and IP networks “meet” when the ATM PVCs are mapped to router logical interfaces. Logical interfaces on a router are associated with ATM PVCs, and then the routing protocol works to associate IP prefixes (routes) with the subinterfaces.
Finally, ATM PVCs are integrated into the IP network by running the IGP across each of the PVCs to establish peer relationships and exchange routing information. Between any two routers, the IGP metric for the primary PVC is set such that it is more preferred than the backup PVC. This guarantees that the backup PVC is used only when the primary PVC is not available. Also, if the primary PVC becomes available after an outage, traffic automatically returns to the primary PVC from the backup.
&lt;number&gt;
In an ATM overlay network, routers surround the edge of the ATM cloud. Each router communicates with every other router by a set of PVCs that are configured across the ATM physical topology. The PVCs function as logical circuits, providing connectivity between edge routers. The routers do not have direct access to information describing the physical topology of the underlying ATM infrastructure. The routers have knowledge only of the individual PVCs that appear to them as simple point-to-point circuits between two routers. The illustration above shows how the physical topology of an ATM core differs from the logical IP overlay topology.
The distinct ATM and IP networks “meet” when the ATM PVCs are mapped to router logical interfaces. Logical interfaces on a router are associated with ATM PVCs, and then the routing protocol works to associate IP prefixes (routes) with the subinterfaces.
Finally, ATM PVCs are integrated into the IP network by running the IGP across each of the PVCs to establish peer relationships and exchange routing information. Between any two routers, the IGP metric for the primary PVC is set such that it is more preferred than the backup PVC. This guarantees that the backup PVC is used only when the primary PVC is not available. Also, if the primary PVC becomes available after an outage, traffic automatically returns to the primary PVC from the backup.
In an ATM overlay network, routers surround the edge of the ATM cloud. Each router communicates with every other router by a set of PVCs that are configured across the ATM physical topology. The PVCs function as logical circuits, providing connectivity between edge routers. The routers do not have direct access to information describing the physical topology of the underlying ATM infrastructure. The routers have knowledge only of the individual PVCs that appear to them as simple point-to-point circuits between two routers. The illustration above shows how the physical topology of an ATM core differs from the logical IP overlay topology.
The distinct ATM and IP networks “meet” when the ATM PVCs are mapped to router logical interfaces. Logical interfaces on a router are associated with ATM PVCs, and then the routing protocol works to associate IP prefixes (routes) with the subinterfaces.
Finally, ATM PVCs are integrated into the IP network by running the IGP across each of the PVCs to establish peer relationships and exchange routing information. Between any two routers, the IGP metric for the primary PVC is set such that it is more preferred than the backup PVC. This guarantees that the backup PVC is used only when the primary PVC is not available. Also, if the primary PVC becomes available after an outage, traffic automatically returns to the primary PVC from the backup.