MPLS NETWORK PDF

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What is MPLS? Where Is it Used? • Label Distribution in MPLS Networks. LDP, RSVP, BGP. • Building MPLS Based Services. VPNs. AToM. Traffic Engineering. There are lot of IP people out there who still don't like MPLS. • Many of the concepts are completely foreign to pure IP networks. • Many parts of MPLS smell like. Each router in the network makes an independent decision when forwarding packets. MPLS helps reduce the number of routing lookups, possibly changes the.


Mpls Network Pdf

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establishes label to destination network mappings. 2. Ingress label Edge Router receives packet, performs. Layer 3 value-added services, and “MPLS” packets. Definition of MPLS. • Multi Protocol Label Switching. – Multiprotocol, it supports ANY network layer protocol, i.e.. IPv4, IPv6, IPX, CLNP, etc. packets. All core routers (identified simply as LSRs) in the MPLS network forward solely based on the label. As a packet traverses the core MPLS network, core.

MPLS plays an important role in engineering the This section contains a brief description of the network to provide efficient services to its customers. A more complete description can be found in [8]. The advantages of MPLS for ternet by using a faster routing table lookup mech- traffic engineering include: anism.

This will act as an universal ware. It supplements share from the available bandwidth. IP so that traffic can be marked, classified and policed. With the use of MPLS, end-to-end quality of service This idea is represented in the following sketch: can finally be achieved [10]. On the We are currently working on the implementation other hand there are more layer2 or layer3 protocols of an MPLS switch using a Linux platform.

This coexisting. A goal of MPLS is to be able to support multiple network-layer protocols hence the name Multiprotocol 7. There are many has been on defining functions and operations for IPv4.

The resulting platform may be used to evaluate alternatives 7 Our project to the proposed MPLS standard implementation and to determine how best to exploit the flexibility of MPLS in bandwidth management.

Another IP router.

This reconfiguration can be done without proposal as described in [12] is to encode the label recompiling the kernel or restarting the system. Two IPv4 stack computers were able to commu- This involves work with data-link layer and network nicate transparently using the MPLS cloud as a part of layer headers, The research started with understanding the network core.

Hence, we studied the Linux protocols and Linux device drivers [13]. The modularity of the Linux kernel [15] menting a protocol for next-generation routed networks. The next step is to implement a sig- kernel module. This protocol module is independent naling mechanism for the existing forwarding protocol.

Thus it can be loaded and This will result in a fairly complete implementation of unloaded dynamically from the running kernel. The the base MPLS standard. This can than be extended to standard approach requires changes in the internal experiment with new ideas for bandwidth management.

This is a major modification since socket buffers are the References structures used by the all Linux protocols. Therefore the kernel has to be recompiled and the system has to [1] Solaris.

Bandwidth management for ip net- be restarted. In our approach we are transparently changing the purpose of an existing MAC field, the destination [2] Eric W. MPLS Implementing the technol- address field. The MPLS module will use it to push, ogy. Addison-Wesley, The other components of the [3] E.

MPLS Tutorial

Rosen, Cisco Systems, A. If Ru has coarser granularity than Rd i. This would require it to withdraw the m labels it has distributed, and distribute n labels.

This is the preferred option. For example, suppose that Ru applies a single label to all traffic that needs to pass through a certain egress LSR, whereas Rd binds a number of different labels to such traffic, depending on the individual destination addresses of the packets.

If Ru knows the address of the egress router, and if Rd has bound a label to the FEC which is identified by that address, then Ru can simply apply that label. Where ordered control is used, this requires each node to know the granularity only for FECs which leave the MPLS network at that node.

For independent control, best results may be obtained by ensuring that all LSRs are consistently configured to know the granularity for each FEC. However, in many cases this may be done by using a single level of granularity which applies to all FECs such as "one label per IP prefix in the forwarding table", or "one label per egress node".

The proposed MPLS protocol architecture supports two options for Route Selection: 1 hop by hop routing, and 2 explicit routing. Hop by hop routing allows each node to independently choose the next hop for each FEC. This is the usual mode today in existing IP networks.

The sequence of LSRs followed by an explicitly routed LSP may be chosen by configuration, or may be selected dynamically by a single node for example, the egress node may make use of the topological information learned from a link state database in order to compute the entire path for the tree ending at that egress node.

Explicit routing may be useful for a number of purposes, such as policy routing or traffic engineering. In MPLS, the explicit route needs to be specified at the time that labels are assigned, but the explicit route does not have to be specified with each IP packet. The procedures for making use of explicit routes, either strict or loose, are beyond the scope of this document.

This can happen due to transient conditions, or due to an error at the LSR which should be the packet's next hop. It is tempting in such cases to strip off the label stack and attempt to forward the packet further via conventional forwarding, based on its network layer header.

However, in general this is not a safe procedure: - If the packet has been following an explicitly routed LSP, this could result in a loop. Unless it can be determined through some means outside the scope of this document that neither of these situations obtains, the only safe procedure is to discard the packet. Whenever a packet passes through a router, its TTL gets decremented by 1; if the TTL reaches 0 before the packet has reached its destination, the packet gets discarded.

MPLS Tutorial

This provides some level of protection against forwarding loops that may exist due to misconfigurations, or due to failure or slow convergence of the routing algorithm. TTL is sometimes used for other functions as well, such as multicast scoping, and supporting the "traceroute" command. If the label values are encoded in a data link layer header e. This means that special procedures must be developed to support traceroute functionality, for example, traceroute packets may be forwarded using conventional hop by hop forwarding.

If the ATM hardware cannot Rosen, et al. Even if fair buffer access can be provided, it is still worthwhile to have some means of detecting loops that last "longer than possible".

All LSRs that may attach to non-TTL LSP segments will therefore be required to support a common technique for loop detection; however, use of the loop detection technique is optional.

Label Encodings In order to transmit a label stack along with the packet whose label stack it is, it is necessary to define a concrete encoding of the label stack. The architecture supports several different encoding techniques; the choice of encoding technique depends on the particular kind of device being used to forward labeled packets.

MPLS Virtual Private Networks

This shim would really be just an encapsulation of the network layer packet; it would be "protocol- independent" such that it could be used to encapsulate any network layer. Hence we will refer to it as the "generic MPLS encapsulation". The generic MPLS encapsulation would in turn be encapsulated in a data link layer protocol.

Therefore if one or more labels can be encoded directly into the fields which are accessed by these legacy switches, then the legacy switches can, with suitable software upgrades, be used as LSRs.

This technique can be used in any network. This technique some advantages over the previous one, in that it permits the use of ATM "VP-switching". However, this technique cannot always be used. Cells from different packets will then carry different VCI values.

As we shall see in section 3. This technique depends on the existence of a capability for assigning bit VCI values to each ATM switch such that no single VCI value is assigned to two different switches. If an Rosen, et al. If there are more labels on the stack than can be encoded in the ATM header, the ATM encodings must be combined with the generic encapsulation.

Therefore, when we discuss the procedures for processing a labeled packet, we speak in abstract terms of operating on the packet's label stack. When a labeled packet is received, the LSR must decode it to determine the current value of the label stack, then must operate on the label stack to determine the new value of the stack, and then encode the new value appropriately before transmitting the labeled packet to its next hop.

Unfortunately, ATM switches have no capability for translating from one encoding technique to another. This is one example of an LSR with different label stack encodings on different hops. When forwarding packets in that FEC, one would like to have a single outgoing label which is applied to all such packets. The fact that two different packets in the FEC arrived with different incoming labels is irrelevant; one would like to forward them with the same outgoing label.

The capability to do so is known as "label merging". Let us say that an LSR is not capable of label merging if, for any two packets which arrive from different interfaces, or with different labels, the packets must either be transmitted out different interfaces, or must have different labels.

This is discussed in more detail in the next section. If a particular LSR cannot perform label merging, then if two packets in the same FEC arrive with different incoming labels, they must be forwarded with different outgoing labels. With label merging, the number of outgoing labels per FEC need only be 1; without label merging, the number of outgoing labels per FEC could be as large as the number of nodes in the network.

With label merging, the number of incoming labels per FEC that a particular LSR needs is never be larger than the number of label distribution adjacencies.

In fact, it is difficult for an LSR to even determine how many such incoming labels it must support for a particular FEC. The issue is somewhat different in the case of datagram media versus the case of ATM.

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The different media types will therefore be discussed separately. In fact, it is possible to use such technologies for MPLS forwarding; a label distribution protocol can be used as the "signalling protocol" for setting up the cross-connect tables. In ATM, if one attempts to perform label merging, the result may be the interleaving of cells from various packets. If cells from different packets get interleaved, it is impossible to reassemble the packets.

Some Frame Relay switches use cell switching on their backplanes. These switches may also be incapable of supporting label merging, for the same reason -- cells of different packets may get interleaved, and there is then no way to reassemble the packets. We propose to support two solutions to this problem. An upstream neighbor which does not support label merging needs to be sent multiple labels per FEC. However, there is no way of knowing a priori how many labels it needs.

In the MPLS architecture, if a particular upstream neighbor does not support label merging, it is not sent any labels for a particular FEC unless it explicitly asks for a label for that FEC.

The upstream neighbor may make multiple such requests, and is given a new label each time.

When a downstream neighbor receives such a request from upstream, and the downstream neighbor does not itself support label merging, then it must in turn ask its downstream neighbor for another label for the FEC in question.

It is possible that there may be some nodes which support label merging, but can only merge a limited number of incoming labels into a single outgoing label.

Suppose for example that due to some hardware limitation a node is capable of merging four incoming labels into a single outgoing label. Suppose however, that this particular node has six incoming labels arriving at it for a particular FEC. In this case, this node may merge these into two outgoing labels.

Whether label merging is applicable to explicitly routed LSPs is for further study. Merge over ATM 3. Methods of Eliminating Cell Interleave There are several methods that can be used to eliminate the cell interleaving problem in ATM, thereby allowing ATM switches to support stream merge: 1.

VC merge When VC merge is used, switches are required to buffer cells from one packet until the entire packet is received this may be determined by looking for the AAL5 end of frame indicator. VP merge has the advantage that it is compatible with a higher percentage of existing ATM switch implementations. This makes it more likely that VP merge can be used in existing networks.

Unlike VC merge, VP merge does not incur any delays at the merge points and also does not impose any buffer requirements. There are a number of ways that this can be accomplished. Selection of one or more methods is for further study. This tradeoff between compatibility with existing equipment versus protocol complexity and scalability implies that it is desirable for the MPLS protocol to support both VP merge and VC merge.

In the case where VC merge and non-merge nodes are interconnected the forwarding of cells is based in all cases on a VC i. If the upstream neighbor is not doing merge, then the Rosen, et al. A similar method is possible to support nodes which perform VP merge.

Furthermore, suppose that a non-merge node is downstream from two different VP merge nodes. Tunnels and Hierarchy Sometimes a router Ru takes explicit action to cause a particular packet to be delivered to another router Rd, even though Ru and Rd are not consecutive routers on the Hop-by-hop path for that packet, and Rd is not the packet's ultimate destination.

For example, this may be done by encapsulating the packet inside a network layer packet whose destination address is the address of Rd itself. This creates a "tunnel" from Ru to Rd. MPLS plays an important role in engineering the This section contains a brief description of the network to provide efficient services to its customers. A more complete description can be found in [8]. The advantages of MPLS for ternet by using a faster routing table lookup mech- traffic engineering include: This will act as an universal ware.

It supplements share from the available bandwidth. IP so that traffic can be marked, classified and policed.

With the use of MPLS, end-to-end quality of service This idea is represented in the following sketch: On the We are currently working on the implementation other hand there are more layer2 or layer3 protocols of an MPLS switch using a Linux platform. This coexisting. A goal of MPLS is to be able to support multiple network-layer protocols hence the name Multiprotocol 7. There are many has been on defining functions and operations for IPv4.

The resulting platform may be used to evaluate alternatives 7 Our project to the proposed MPLS standard implementation and to determine how best to exploit the flexibility of MPLS in bandwidth management. Another IP router. This reconfiguration can be done without proposal as described in [12] is to encode the label recompiling the kernel or restarting the system. Two IPv4 stack computers were able to commu- This involves work with data-link layer and network nicate transparently using the MPLS cloud as a part of layer headers, The research started with understanding the network core.

Hence, we studied the Linux protocols and Linux device drivers [13]. The modularity of the Linux kernel [15] menting a protocol for next-generation routed networks. The next step is to implement a sig- kernel module. This protocol module is independent naling mechanism for the existing forwarding protocol. Thus it can be loaded and This will result in a fairly complete implementation of unloaded dynamically from the running kernel.

The the base MPLS standard. This can than be extended to standard approach requires changes in the internal experiment with new ideas for bandwidth management. This is a major modification since socket buffers are the References structures used by the all Linux protocols. Therefore the kernel has to be recompiled and the system has to [1] Solaris. Bandwidth management for ip net- be restarted.

In our approach we are transparently changing the purpose of an existing MAC field, the destination [2] Eric W. MPLS Implementing the technol- address field. The MPLS module will use it to push, ogy. Addison-Wesley, The other components of the [3] E. Rosen, Cisco Systems, A. Viswanathan, Linux networking system will not be affected by the Force10 Networks, R.

SD-WAN Gets (More) Real for Service Providers

Callon, and Juniper Net- change with one exception. The Ethernet interface must works. Multiprotocol label switching architecture.This capability eliminates the need to run a particular routing protocol on all the devices. This is also the router that decides the LSP the packet will take until it reaches its destination address.

Although, as we shall see, MPLS supports a hierarchy, the processing of a labeled packet is completely independent of the level of hierarchy. In the MPLS architecture, if a particular upstream neighbor does not support label merging, it is not sent any labels for a particular FEC unless it explicitly asks for a label for that FEC.

Aggregation may reduce the number of labels which are needed to handle a particular set of packets, and may also reduce the amount of label distribution control traffic needed. The only exception is policy-based routing PBR , which bypasses the destination-based routing lookup. Cells from different packets will then carry different VCI values. With label merging, the number of outgoing labels per FEC need only be 1; without label merging, the number of outgoing labels per FEC could be as large as the number of nodes in the network.

Labels are small identifiers inserted by the ingress The aim of traffic engineering is to find mechanisms to LSR, and removed by the egress LSR.

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