MEN Part 2- Day2 -Ver1_NoRestriction

8/14/2019 MEN Part 2- Day2 -Ver1_NoRestriction

1/35

Network Learning CentreProprietary & Confidential

11

MEN Part 2

50467565


2/35


22

Agenda

Day2

Module 2

o MPLS


3/35


33

Module 2

MPLS


4/35


44

Page 4

MPLS

MPLSMulti-Protocol Label Switching Multi-Protocol

Support multiple Layer-3 protocols, such asIP, IPv6, IPX, SNA

Label Switching

Label packets, and replace IP forwardingwith label switching

MPLS is the abbreviation of Multi-Protocol Label Switching. MP means

it support more than one protocol, such as IP, IPv6, IPX, SNA, etc. as we

know, in IP network, the routers forwarding packets by using packets

destination IP address and looking for the IP routing table to get the next hop,

while in MPLS network, we using label to forward the packets, named labelswitching. MPLS uses a short label of fixed length to encapsulate packets.

MPLS use FEC (Forwarding Equivalent Class) to classify the forwarding

packets. The packets of the same FEC are treated the same in the MPLS

network. later we will introduce the FEC.

By adding a label to the packet at the entrance of MPLS network, the

packet is forwarded by label switching, some thing like ATM Switching. And

when leaving the MPLS network, the label added is removed and the label

packet is restored to original protocol packet.

For more details about MPLS, refer to RFC 3031 (Multi-protocol Label

Switching Architecture).


5/35


55

Page 5

Origin: To Integrate IP with ATM

Connectionlesscontrol plane

Connectionlessforwarding plane

IP

Connection-orientedcontrol plane

Connection-orientedforwarding plane

ATM

Connectionlesscontrol plane

Connection-orientedforwarding plane

MPLS

MPLS originates from the Internet Protocol version 4 (IPv4). Before MPLS

generation, IP network forwarding packets with IP routing table, by looking for the

IP routing table with packets destination IP address and get the next hop, as each

forwarded packet need to look for the IP routing table, the efficiency is low.

Another packet forwarding technology is ATM, forward packet by VPI/VCI

switching, a type of label switching, the efficiency is higher than IP forwarding. IP

network, its control plane is connectionless, and forwarding plane also is

connectionless, just hop by hop, each hop decide to choose the next hop. while

ATM, its control plane is connection-oriented, if many device need to set up the

connection with each other, the configuration is very heavy, and with label

switching, the forwarding plane is connection-oriented, the packet forwarding path

is defined before.

MPLS integrates both of the two forwarding technologies. Its control plane isconnectionless, easy to widen its network, and forwarding plane is connection-

oriented, before data forwarding, LSP need to be set up, and is available to manager

and control the setting up.


6/35


66

Page 6

Connection-oriented Features

Connectionless: packet route

Path 1 = S1, S2, S6, S8

Path 2 = S1, S4, S7, S8

The data reach their destinationout of order along differentpaths

connection-oriented: cell switching

VC = S1, S4, S7, S8

The data reach their destination inorder along the same connection

Fixed time delay, easy to control Connection types: PVC SVC

S2 S6

S4 S7

S3 S5

S1 S8

1

1

1

2 2

2

S2 S6

S4 S7

VC

S1 S8S3 S5

As for connectionless packet forwarding, the data reach their destination out of

order, because each packet choose its forwarding path independently, and usually

the path will be different and the time delay of each packet also will be different, so

the sending sequence and the arriving sequence will be different. While the

connection-oriented packet switching, the forwarding path is fixed and then time

delay is fixed and the sending sequence and arriving sequence are the same. And it

is easy to control. There have two connection type: PVC (Permanent Virtual

Circuit) and SVC (Switched Virtual Circuit)


7/35


77

Page 7

Basic MPLS Concepts

LSR: Label Switch Router

LER: Label Edge Router

LSP: Label Switch Path

LER

LER

LER

LER

LSR LSR

LSR

MPLS domain

IP

MPLS

LSP

Some basic concepts in MPLS:

LSR is the basic component of the MPLS network. The network consisting of

LSRs, is called an MPLS domain. The LSR located at the edge of the domain and

having a neighbor not running MPLS is an edge LSR, also called Labeled Edge

Router (LER).

The LSR located inside the domain is called a core LSR. The core LSR can be

either a router that supports MPLS or an ATM-LSR upgraded from an ATM switch.

MPLS runs between LSRs in the domain, and IP runs between an LER and an router

outside the domain.

The LSRs along which labeled packets are transmitted form an LSP.


8/35


9/35


99

MPLS Packet Flow


10/35


1010

Page 10

MPLS Advantages

Replace IP header with short and fixed-length labels as forwarding basis toimprove forwarding speed

Better integrate IP with ATM

Provide value-added service withoutprejudice to efficiency:

VPN

Traffic engineering

QOS

MPLS technologys original intention is used to replace IP forwarding with

label switching to improve the forwarding efficiency, while with the development of

router technology, software based forwarding mechanism is replaced by hardware

based forwarding mechanism, the speed is higher than software based MPLS label

forwarding, so it is not exact to say that MPLS improve forwarding speed now.

Now the most charm of MPLS is that it can provide many value-added service

such as follows:

1.MPLS VPN

2.MPLS Traffic Engineering

3.MPLS Qos


11/35


1111

Page 11

MPLS Encapsulation Format and Label

MPLS headerLayer 2

headerIP header Data

Label SEXP TTL

200 23 24 31

32 bits

A label is a short, fixed length, locally significant identifier which is used to

identify a FEC. The label which is put on a particular packet represents the

Forwarding Equivalence Class to which that packet is assigned.

Most commonly, a packet is assigned to a FEC based (completely or partially)

on its network layer destination address. However, the label is never an encoding of

that address.

A label contains four fields:

Label: 20 bits, represents label value, and used as the pointer for

forwarding.

Exp: 3 bits, reserved, used for experiments, and generally used as Class of

Service (CoS).

S: 1 bit, represents label stack. The value 1 refers to the bottom layer label.

Just 0 means next head is MPLS header and 1 means next header is IP

header.

TTL: 8 bits, represents time to live, and has the same meaning as the TTL

in the IP packet.


12/35

A value of 0 represents the "IPv4 Explicit NULL Label". This label value is

only legal at the bottom of the label stack. It indicates that the label stack must be

popped, and the forwarding of the packet must then be based on the IPv4 header.

A value of 1 represents the "Router Alert Label". This label value is legal

anywhere in the label stack except at the bottom. When a received packet contains

this label value at the top of the label stack, it is delivered to a local software

module for processing. The actual forwarding of the packet is determined by the

label beneath it in the stack. However, if the packet is forwarded further, the Router

Alert Label should be pushed back onto the label stack before forwarding. The use

of this label is analogous to the use of the "Router Alert Option" in IP packets .

Since this label cannot occur at the bottom of the stack, it is not associated with a

particular network layer protocol.

A value of 2 represents the "IPv6 Explicit NULL Label". This label value is

only legal at the bottom of the label stack. It indicates that the label stack must be

popped, and the forwarding of the packet must then be based on the IPv6 header.

A value of 3 represents the "Implicit NULL Label". This is a label that an LSR

may assign and distribute, but which never actually appears in the encapsulation.

When an LSR would otherwise replace the label at the top of the stack with a new

label, but the new label is "Implicit NULL", the LSR will pop the stack instead of

doing the replacement. Although this value may never appear in the encapsulation,

it needs to be specified in the Label Distribution Protocol, so a value is reserved.


13/35

A label space refers to the value range of labels that can be allocated to LDP

peers. You can specify a label space for each interface of an LSR (per interface

label space) or for the entire LSR (per platform label space).

Platform-wide means the label should be unique with all the interfaces on the

device; interface-specific means the label should be unique with one interface,

while different interface of the device, the label value could be the same.

LDP is the protocol used to distribute the label, how can we identify the type

of generated label. LDP choose the < LSR ID> :< Label Space ID >, LSR ID

Globally unique value of an LSR (4 octets); Label space IDZero for platform-

wide label space (2 octets). For example, identifier 192.168.1.1:0 means platform-

wide, identifier 192.168.1.1:5 means interface-specific.

With different encapsulation mode, MPLS based device choose different

label space:

MPLS based frame mode use Platform-wide label space, such as IP,

Ethernet.

MPLS based cell mode use Per-interface label space, such as ATM


14/35


1414

Page 14

MPLS TTL Processing

Consider the entire MPLS domain as one hop

IP TTL --MPLS TTL255 MPLS TTL -- IP TTL --

Ingress LER LSR Egress LER

Include IP TTL in MPLS TTL

IP TTL --

MPLS TTLIP TTL MPLS TTL --

MPLS TTL --

IP TTLMPLS TTL

Ingress LER LSR Egress LER

The MPLS label comprises an 8-bit TTL field, which is similar to that in an IP

header. TTL is also used in the trace route function. As described in RFC 3031, an

LSR node needs to copy the TTL value of the IP packet or that of the upper layer

label to the TTL field of the added label. When LSR forwards a labeled packet, the

TTL value of the label at the top of the label stack decrements by 1. When the label

is out of the label stack, the LSR copies the TTL value at the top of the stack to the

IP packet or lower layer label.

Before the LSP transverses the non-TTL LSP segment formed by ATM-LSRs

or FR-LSRs, the TTL should be processed uniformly because the LSRs within that

domain cannot process the TTL field. That is, the value of the length in this non-

TTL LSP segment should be decremented by 1 on entering the segment.

In MPLS VPN applications, you can hide the MPLS backbone network

structure for security. The VRP supports different TTL propagation settings for

VPN packets and public packets.


15/35


1515

Page 15

Label Stack

Theoretically, label stack enableslimitless nesting to provide infiniteservice support. This is simply thegreatest advantage of MPLS

technology.

MPLSheader

Layer2header IP header Data

MPLSheader

Theoretically, label stack enables limitless nesting to provide infinite service

support. This is simply the greatest advantage of MPLS technology. In real use, up

to now there usually no more than four labels in packet. Each label use S bit to mark

the bottom label. The value 1 means the bottom layer label.

In layer2 header how to identify the higher layers protocol? In PPP there add a

new type of NCP called MPLSCP, identified with 0x8281. while in Ethernet 0x8847

means unicast MPLS, 0x8848 means multicast and 0x0800 means IP packet.

The label stack follow FIFO, label process from the top stack. When executing

MPLS forwarding, only use the outer side label.


16/35


1616

MPLS Architecture

Router functionality is divided into two major parts: controlplane and data plane

Data PlaneData Plane

Control PlaneControl Plane

OSPF: 10.0.0.0/8OSPF: 10.0.0.0/8

LDP: 10.0.0.0/8Label 17

LDP: 10.0.0.0/8Label 17

OSPF

LDP

LFIB

LDP: 10.0.0.0/8Label 4

LDP: 10.0.0.0/8Label 4

OSPF: 10.0.0.0/8OSPF: 10.0.0.0/8

417Labeled packet

Label 4

Labeled packetLabel 4




17/35


1717

Edge-LSR Architecture

LIB

LFIB


18/35


1818

Page 18

Basic Concepts of Label Forwarding

FEC (Forwarding Equivalence Class): Import the packets withidentical characteristics into the same LSP

Huawei Terms

NHLFE (Next Hop Label Forwarding Entry): Describe labeloperations

next hop

label operation types: push/pop/swap/null

Link layer encapsulation types

FTN (FEC to NHLFE): Map FEC to NHLFE (ingress operation)

ILM (Incoming Label Map): Map MPLS label to NHLFE (egressoperation)

Cisco Terms LFIB Lable Forwarding Information Base

MPLS is a high-performance forwarding technology that takes the packets with

the same forwarding mode as a class. This kind of class is called Forwarding

Equivalent Class (FEC). The packets of the same FEC are treated the same in the

MPLS network. The source address, destination address, source port, destination

port, protocol type, Virtual Private Network (VPN) or any of these combinations

can determine an FEC. For example, packets transmitted to the same destination

through the longest matching algorithm belong to an FEC.

Next Hop Label Forwarding Entry (NHLFE): indicates the action to be

performed on a label, such as push, pop and swap.

FEC to NHLFE map (FTN): indicates the mapping for an FEC to NHLFE on

the ingress.

Incoming Label Map (ILM): indicates the mapping process of the received labelto NHLFE on the transits and egress.


19/35


1919

Page 19

Label Forwarding

The traditional routing protocol and Label Distribution Protocol (LDP) serve to create routingtable and label mapping table (FEC-Label mapping) in each LSR for FECs with servicerequirement, i.e. create LSP successfully.

Ingress LER receives a packet, determines the FEC that the packet belongs to, and label thepacket

In MPLS domain, packets are forwarded in accordance with labels and label forwarding table viathe forwarding unit

Egress LER removes the label and continues forwarding the packet

Parse IP headerFEC bound with LSPFTN->NHLFE

ILM->NHLFE

ILM->NHLFE

Parse IP headerdistribute FEC

mapped to next hopILM->NHLFE

Ingress LER LSR LSR Egress LER

Label operation: pushLabel operation: swap Label operation: swap

label operation: pop

A B C D

On the ingress, the packets entering the network are classified into various

FECs by their characteristics. Usually, FEC classification is done based on the

destination IP address prefix or host address. The packets belonging to the same

FEC will have the same label and pass through the same path in the MPLS domain.

LSR assigns a label for an incoming packet, and then forwards it through a specified

interface.

On the transits along the LSP, the mapping table of the incoming and outgoing

labels is established. The element of this table is referred to as NHLFE. When a

labeled packet arrives, LSR only needs to find the corresponding NHLFE from the

table according to the incoming label and replace the original label with the new

outgoing label, and then forward the labeled packet. This process is called ILM.

Therefore, this method is much simpler, and the forwarding is faster.

On the LER, it removes the label and continues forwarding the packet .


20/35


2020

Page 20

NHLFE/LFIB

A:

Add label L1E1B10.0.1.0/24

OthersLabel operationTransmitting interfacenext hop

NHLFE

FEC

Remove the previous label and add L2E1CL1

Otherslabel operationTransmitting interfaceNext hop

NHLFEIngress

label

B:

Remove the previous label and add L3DL2

OthersLabel operationNext hop

NHLFEIngress

label

C:

E1Transmitting interface

The "Next Hop Label Forwarding Entry" (NHLFE) is used when forwarding a

labeled packet. It contains the following information:

1. the packet's next hop

2. the operation to perform on the packet's label stack; this is one of the followingoperations:

a) replace the label at the top of the label stack with a specified new label

b) pop the label stack

c) replace the label at the top of the label stack with a specified new label, and then

push one or more specified new labels onto the label stack.


21/35


2121

Page 21

Penultimate Hop Popping (PHP)

The label at the outmost layer does not make any sense to the last hop. Thus, it

is advisable to pop the label at the last hop but one to ease the burden of the

last hop.

If there is only one layer of label, the last hop will perform IP forwarding directly;otherwise, it will perform the internal label forwarding.

Parse IP headerDistribute FEC

Mapped to next hop

Label operation: popParse IP headerFEC bound with LSP

FTN->NHLFEILM->NHLFE ILM->NHLFE

Ingress LER LSR LSR Egress LER

Label operation: pushLabel operation: swap

In the MPLS network, LSR forwards packets according to its label. On the

egress, the label is removed and the packet is forwarded as an IP packet.

In some MPLS applications, the egress requires only IP forwarding. The MPLS

label has no meaning for forwarding. In such conditions, you can use Penultimate

Hop Popping (PHP) to pop the label at the penultimate node, saving label operation

on the egress. The PHP feature should be configured on the egress, depending on

whether the penultimate node supports PHP.

According to the description in RFC 3032 (MPLS Label Stack Encoding):

Label value 0 stands for IPv4 explicit-null. This value is valid only when it

appears at the bottom of label stack. It indicates that the local node must pop the

label, and IP forwarding will be performed on the next node. Label value 3 stands

for implicit-null. This value will not appear in the label stack. When an LSR isallocated an implicit-null label, it will not use this value to replace the original

value, but perform the pop operation directly.


22/35


2222

Various MPLS Application and theirInteraction

Every MPLS application has the same set of components as the IP routingapplication:

A database defining the Forward Equivalence Classes (FECs) table for theapplication (the IP routing table in an IP routing application)

Control protocols that exchange the contents of the FEC table between theLSRs (IP routing protocols or static routing in an IP routing application)

Control process that performs label binding to FECs and a protocol toexchange label bindings between LSRs (TDP or LDP in an IP routingapplication)

Optionally, an internal database of FEC-to-label mapping (LabelInformation Base in an IP routing application)

Each application uses its own set of protocols to exchange FEC table or FEC-to-label mapping between nodes.


23/35


24/35


2424

Control Protocols Used in Various MPLSApplications

Application FEC Table

Control Protocol Used toBuild FEC Table

Control Protocol Used toExchange FEC-to-LabelMapping

IP routing IP routing table Any IP routing protocol

Tag Distribution Protocol(TDP) or Label DistributionProtocol (LDP)

Multicast IP routing Multicast routing table PIM PIM version 2 extensions

VPN routing Per-VPN routing table

Most IP routing protocolsbetween service providerand customer, MultiprotocolBGP inside the serviceprovider network

Multiprotocol BGP

Traffic engineering MPLS tunnels definition

Manual interfacedefinitions, extensions toIS-IS or OSPF

RSVP

MPLS Quality of Service IP routing table IP routing protocols Extensions to TDP/ LDP


25/35


2525

Page 25

Several Issues Concerning LabelDistribution

Label allocation mode

DoD : downstream-on-demand

DU: downstream unsolicited

Label control mode

Ordered

Independent

Label retention mode

Conservative retention mode : upon receiving a label, if there is no

route destined for corresponding FEC, discard the label.

Liberal mode: upon receiving a label, if there is no route destined forthe corresponding FEC, hold the label for later use.

In the MPLS architecture, the downstream LSR binds a label to a particular

FEC, and then notifies the upstream LSR. That is to say, the label is specified by the

downstream LSR, and the assigned label is distributed from downstream to

upstream. There have several work mode about the labels allocation, control and

retention.

Label allocation mode

DoD : downstream-on-demand

DU: downstream unsolicited

Label control mode

Ordered

Independent

Label hold mode

Conservative retention mode

Liberal mode


26/35


2626

Page 26

Label Allocation Mode: DoD

Upstream Downstream

The upstream LSR sends a label request (containing FEC description

information) to the downstream LSR.

The downstream LSR allocates a label to this FEC and feeds back the boundlabel to the upstream LSR via the label mapping message.

171.68.10.0/24171.68.40.0/24

LSR1 LSR2 LSR3

Requestinglabeldestinedfor171.68.10.0/24

Requestinglabeldestinedfor171.68.10.0/24

20Label20isallocatedto171.68.10.0/24

Label18isallocatedto171.68.10.0/24Routetriggering

In DoD mode, the label is distributed in this way: the upstream sends a label

request message containing FEC descriptive information to the downstream, and the

downstream distributes a label for this FEC, and then sends the label mapping

message with the label to the upstream.

When the downstream feeds back the label mapping message depends on its

label control mode.

If the ordered mode is used, the message is sent back to its upstream LSR only

when the downstream has received a label mapping message for the FEC from its

downstream LSR.

If the independent mode is used, the downstream will send a label mapping

message to its upstream LSR immediately, no matter whether it has received the

label mapping message for the FEC from its downstream LSR or not.

Usually, the upstream LSR selects the downstream LSR according to the

information in its routing table.


27/35


2727

Once the LDP session is set up successfully, the downstream LSR will

initiatively advertise the label mapping message to its upstream LSR.

The upstream router will save the label in the label mapping table.

171.68.40.0/24Upstream

Downstream

RoutetriggeringLabel20canbeusedtoreach

171.68.10.0/24

Label18canbeusedtoreach171.68.10.0/24

Page 27

Label Allocation Mode: DU

171.68.10.0/24

In DU mode, the label is distributed in the following way: when an LDP

session is established successfully, the downstream LSR will actively distribute

label mapping messages to its upstream LSR. The upstream LSR saves the label

mapping information and processes the received label mapping information

according to the routing table.


28/35


2828

Upstream

Upstream Downstream

Downstream

DU+ Ordered

Page 28

Label Control Mode: Ordered

Not until it receives a label mapping message from its downstream LSP will it

send the message upstream

DOD+ Ordered

When using LSP ordered control, an LSR may initiate the transmission of a

label mapping only for a FEC for which it has a label mapping for the FEC next

hop, or for which the LSR is the egress. For each FEC for which the LSR is not the

egress and no mapping exists, the LSR MUST wait until a label from a downstream

LSR is received before mapping the FEC and passing corresponding labels to

upstream LSRs. An LSR may be an egress for some FECs and a non-egress for

others. An LSR may act as an egress LSR, with respect to a particular FEC, under

any of the following conditions:

1.The FEC refers to the LSR itself (including one of its directly attached interfaces).

2. The next hop router for the FEC is outside of the Label Switching Network.

3. FEC elements are reachable by crossing a routing domain boundary, such as

another area for OSPF summary networks, or another autonomous system for OSPFAS externals and BGP routes

Note that whether an LSR is an egress for a given FEC may change over time,

depending on the state of the network and LSR configuration settings.


29/35


2929

DownstreamUpstream

DownstreamUpstream

DU+ independent

DOD+ independent

It will send upstream a label mapping message immediately, without waiting for alabel mapping message from its downstream LSR

Page 29

Label Control Mode: Independent

When using independent LSP control, each LSR may advertise label mappings

to its neighbors at any time it desires. For example, when operating in independent

Downstream on Demand mode, an LSR may answer requests for label mappings

immediately, without waiting for a label mapping from the next hop. When

operating in independent Downstream Unsolicited mode, an LSR may advertise a

label mapping for a FEC to its neighbors whenever it is prepared to label-switch that

FEC. A consequence of using independent mode is that an upstream label can be

advertised before a downstream label is received.


30/35


3030

Page 30

Label Retention: ConservativeRetention Mode

An LSR stores only the labels receivedfrom next-hop LSRs; all other labels areignored.

LSR1 LSR2 LSR3 LSR4

LSR5

172.16.2/24

mapping

label 20mappinglabel 30

mappinglabel 17

mappinglabel 16

Drop

In Downstream Unsolicited advertisement mode, label mapping

advertisements for all routes may be received from all peer LSRs. When using

conservative label retention, advertised label mappings are retained only if they

will be used to forward packets (i.e., if they are received from a valid next hop

according to routing). If operating in Downstream on Demand mode, an LSR willrequest label mappings only from the next hop LSR according to routing. Since

Downstream on Demand mode is primarily used when label conservation is desired

(e.g., an ATM switch with limited cross connect space), it is typically used with the

conservative label retention mode.

The main advantage of the conservative mode is that only the labels that are

required for the forwarding of data are allocated and maintained. This is

particularly important in LSRs where the label space is inherently limited, such as

in an ATM switch. A disadvantage of the conservative mode is that if routing

changes the next hop for a given destination, a new label must be obtained from the

new next hop before labeled packets can be forwarded.


31/35


3131

Page 31

Label Retention: Liberal RetentionMode

LSR1 LSR2 LSR3 LSR4

LSR5

172.16.2/24

mapping

label 20mapping

label 30

mapping

label 17

mapping

label 16

store

Every LSR stores the received label in its LIB, even when the label

is not received from a next-hop LSR.

In Downstream Unsolicited advertisement mode, label mapping

advertisements for all routes may be received from all LDP peers. When using

liberal label retention, every label mappings received from a peer LSR is retained

regardless of whether the LSR is the next hop for the advertised mapping. When

operating in Downstream on Demand mode with liberal label retention, an LSRmight choose to request label mappings for all known prefixes from all peer LSRs.

Note, however, that Downstream on Demand mode is typically used by devices

such as ATM switch-based LSRs for which the conservative approach is

recommended.

The main advantage of the liberal label retention mode is that reaction to

routing changes can be quick because labels already exist. The main disadvantage

of the liberal mode is that unneeded label mappings are distributed and maintained.


32/35


3232

Label Distribution Protocol (LDP)Label Distribution Protocol (LDP)

LSPs can be defined explicitly for every FEC by networkadministrator or dynamically using LDP.

1

1

LER LERLSR

2

1

0 2 4

Request for label128.89.25.4 Data

12

Request for label

8

LERs assign a label, corresponding to a LSP, to each IP datagram as it is transmitted

towards the destination.Thereafter, at each corresponding hop, the label is used to forward the packet to its nexthop. Two protocols for label request LDP and RSVP-TEBoth LDP and RSVP-TE create LSPs by first sending label requests through thenetwork hop-by-hop to the egress point.

Ingress LER makes a request to upstream router for Label to be used.


33/35

Look carefully about the label forwarding table, there have IN interface and IN

label, OUT interface and OUT label. As for IN label, this label means that I (stand

for this router) distribute to the others, the OUT label means that the other routers

distribute to me, I will put it to the packet. As for some special label value such as 3,

the operation is pop, the label will be removed.

From this table we can view that IN label is different (if it is platform-wide),

and OUT label there may have some same values, why?

Perhaps one is that the label is distributed by different next hop device, they

generate the labels independently, the other is the same route item such as

10.1.1.0/24 in this table, there have several different IN interface such as Serial0 and

Serial1.


3333

Page 33

Label Forwarding Table

IN interface IN label Prefix/MASK OUT interface

(next hop)

OUT label

Serial0 50 10.1.1.0/24 Eth03.3.3.3 80

Serial1 51 10.1.1.0/24 Eth03.3.3.3 80

Serial1 62 70.1.2.0/24 Eth03.3.3.3 52

Serial1 52 20.1.2.0/24 Eth14.4.4.4 52

Serial2 77 30.1.2.0/24 Serial35.5.5.5) 3pop

The in and out is correspond to the label swapnot the labeldistribution.

The in label is that I distribute to the others, I will not put it to

the packet

The out label is the others distribute to me, I will put it to thepacket


34/35


3434

1a. Existing routing protocols (e.g. OSPF, IS-IS)establish reachability to destination networks

1b. Label Distribution Protocol (LDP)establishes label to destinationnetwork mappings.

2. Ingress Edge LSR receives

packet, performs Layer 3 value-added services, and labelspackets

4. Edge LSR ategress removes

label and deliverspacket

3. LSR switchespackets using labelswapping

MPLS Operation Re-Cap


35/35


3535

ThankYou

Documents

MEN Part 2- Day2 -Ver1_NoRestriction