mpls lab with basic configuration

8/12/2019 MPLS Lab With Basic Configuration

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Lab

MPLS Basic ConfigurationLast Update 2011.06.01

1.0.0

Copyright 2011 Kenneth M. Chipps Ph.D.www.chipps.com

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What is MPLS

MPLS is the next development in privately

managed shared networks

Large networks have migrated from

dedicated T carrier circuits directly

connecting sites to each other, to the first

shared service provider network based on

Frame Relay, to now MPLS

MPLS uses tunnels between sites to carry

traffic needing different types of QoSCopyright 2011 Kenneth M. Chipps Ph.D. www.chipps.com 2


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What is MPLS

The source work on MPLS is defined in

RFC 3031

MPLS flows are connection-oriented and

packets are routed along paths pre-

configured by service providers called LSP

- Label Switched Paths

Copyright 2011 Kenneth M. Chipps Ph.D. www.chipps.com 3


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What is MPLS

Basic MPLS has been extended with a set

of Generalized MPLS extensions that

allow it to handle different types of traffic

between the same general end points



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Operation of MPLS

Metaswitch provides an excellent

discussion and graphic to show how

MPLS works

They say

MPLS works by tagging the traffic, in this

example packets, with an identifier, a label, to

distinguish the LSPs



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Operation of MPLS

When a packet is received, the router uses

this label and sometimes also the link over

which it was received to identify the LSP

It then looks up the LSP in its own forwardingtable to determine the best link over which to

forward the packet, and the label to use on

this next hop

A different label is used for each hop, and it is

chosen by the router or switch performing the

forwarding operation



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Operation of MPLS

This allows the use of very fast and simple

forwarding engines, which are often

implemented in hardware

Ingress routers at the edge of the MPLSnetwork classify each packet potentially using

a range of attributes, not just the packet's

destination address, to determine which LSP

to use



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Operation of MPLS

Inside the network, the MPLS routers use only

the LSP labels to forward the packet to the

egress router

Here is their graphic on this



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Operation of MPLS



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Operation of MPLS

The MPLS label is a four-byte, fixed-

length, locally-significant identifier

According to Cisco it looks like this



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Operation of MPLS



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Operation of MPLS

Cisco also says

This label is placed between the data link

layer header and network layer

The top of the label stack appears first in the

packet, and the bottom appears last

The network layer packet immediately follows

the last label in the label stack

Copyright 2011 Kenneth M. Chipps Ph.D. www.chipps.com12


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Operation of MPLS

Copyright 2011 Kenneth M. Chipps Ph.D. www.chipps.com

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Types of MPLS Links

There are many types of MPLS

connections to a service providers MPLS

network

For example, ATT supports MPLS

connections through what they call IP

VPNs

As they say


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Types of MPLS Links

Network-based VPN

Deployed on the AT&T global network, which uses

multiprotocol level switching (MPLS) to provide

high-performance, any-to-any communicationaround the globe


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What is Traffic Engineering

Metaswitch says this about traffic

engineering in MPLS networks

Traffic Engineering is the process where data

is routed through the network according to amanagement view of the availability of

resources and the current and expected traffic

The class of service and quality of servicerequired for the data can also be factored into

this process


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Traffic Engineering may be under the control

of manual operators

They monitor the state of the network and

route the traffic or provision additionalresources to compensate for problems as

they arise

Alternatively, Traffic Engineering may be

driven by automated processes reacting to

information fed back through routing protocols

or other meansCopyright 2011 Kenneth M. Chipps Ph.D. www.chipps.com 17


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Traffic Engineering helps the network provider

make the best use of available resources,

spreading the load over the layer 2 links, and

allowing some links to be reserved for certainclasses of traffic or for particular customers



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There are currently two label distribution

protocols that provide support for Traffic

Engineering

RSVP - Resource ReSerVation Protocol CR-LDP - Constraint-based Routed Label

Distribution Protocol



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MPLS and Traffic Engineering

MPLS and Traffic Engineering work

together to provide tunnels that carry a

certain class of service from one point to

another



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MPLS in a Lab Environment

As it is difficult to create a real MPLS

network in a lab environment and since

simulation programs do not offer a MPLS

cloud as they do for Frame Relay, this labwill use the GNS3 emulation program



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MPLS Lab

This lab is mostly copied from a Cisco

Networking Academy CCNP level lab titled

Lab 4.1 Configuring Frame Mode MPLS



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MPLS Lab

Here is the topology to create in GNS3



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MPLS Lab



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MPLS Lab

In this lab, you will configure a network

using EIGRP as the routing protocol

Then run MPLS over the IP internetwork to

fast-switch Layer 2 frames

Here is the configuration for each router



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R1

enable

config t

interface loopback 0 ip address 172.16.1.1 255.255.255.0

interface fastethernet 0/0

ip address 172.16.12.1 255.255.255.0 no shutdown

exitCopyright 2011 Kenneth M. Chipps Ph.D. www.chipps.com 26


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R1

router eigrp 1

no auto-summary

network 172.16.0.0 interface fastethernet 0/0

mpls ip

exit end



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R2

enable

config t


interface fastethernet 0/0




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R2

interface serial 1/0

ip address 172.16.23.2 255.255.255.0

clockrate 64000 no shutdown

exit



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R2

router eigrp 1

no auto-summary


mpls ip

exit end



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R3

enable

config t


interface serial 1/0


exitCopyright 2011 Kenneth M. Chipps Ph.D. www.chipps.com 31


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R3

router eigrp 1

no auto-summary


mpls ip

exit end



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Check Connectivity

When everything is configured, ping from

R1 to R3

ping 172.16.3.1

Check the routing table

show ip route



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Check Connectivity



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Check Connectivity

On R1, if you perform a traceroute to the

R3s loopback, you see the path the

packet follows

Observe this

This output changes slightly once we

configure MPLS



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Check Connectivity



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MPLS Configuration

As discussed earlier MPLS is a

standardized protocol that allows routers

to switch packets based on labels, rather

than route switch packets based onstandards in the protocols routing formula



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MPLS Configuration

Under normal IP routing, every

intermediate system looks up the

destination prefix of an IP packet in the

Routing Information Base of a router or inthe Forwarding Information Base of a fast

switch at every Layer 3 node



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MPLS Configuration

Instead of switching that is based on

prefix, the first router running MPLS can

encapsulate the IP packet in an MPLS

frame and then further encapsulate thepacket in the Layer 2 frame before

sending it across one of many supported

Layer 2 media



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MPLS Configuration

Configuring the interface-level command

mpls ip on an interface tells the router to

switch MPLS packets inbound and

outbound on that interface as well asattempt to bring up MPLS adjacencies with

the LDP - Label Distribution Protocol out

that egress interface



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MPLS Configuration

LDP facilitates communication between

MPLS peers by allowing them to inform

each other of labels to assign packets to

particular destinations based on Layer 2,Layer 3, or other significant information



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Verify MPLS Configuration

MPLS has many show commands that you

can use to verify proper MPLS operation

Issue the

show mpls interfaces

command to see a quick summary of

interfaces configured with MPLS

Keep in mind that you will see this output

because you applied the mpls ip command

to these interfacesCopyright 2011 Kenneth M. Chipps Ph.D. www.chipps.com 44


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Issue the

show mpls ldp discovery

command to find out local sources for LDP

exchanges and the show mpls ldp

neighbor command to show LDP

adjacencies

Notice that MPLS chooses its IDs basedon loopback interfaces, similar to other

protocols such as OSPF and BGPCopyright 2011 Kenneth M. Chipps Ph.D. www.chipps.com 46


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In the configuration you set up, all routers

are acting as Label Switch Routers and

running LDP

On LSRs, each forwarding equivalence

class - in this case, each routable IP prefix

- is assigned an MPLS label

LDP automatically distributes labels topeers to be used when sending traffic to

specific destinations through the LSRCopyright 2011 Kenneth M. Chipps Ph.D. www.chipps.com 48


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Once labels have been distributed,

switching for MPLS packets is done

through the LIB - Label Information Base

Display the contents of the LIB using

show mpls ldp bindings

There is a binding for every routed prefix;

however, the bindings may vary fromrouter to router since they can get

swapped at each hopCopyright 2011 Kenneth M. Chipps Ph.D. www.chipps.com 49


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In a larger network, the way labels are

swapped is easier to see



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As mentioned earlier, traceroute would

differ slightly once MPLS was set up

The output now includes labels for each

hop

Unfortunately, because of the size of this

network, you only see one label

In a larger network, you would see more

hops, and therefore more labels



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Because you are adding in extra header

information to packets, the MTU of

packets can change

Remember that each MPLS header is 4bytes

The default MTU size of MPLS packets is

taken from the interface it is running on,which in the case of Ethernet is 1500

bytesCopyright 2011 Kenneth M. Chipps Ph.D. www.chipps.com 54


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For this lab, we will change the Ethernet

connection between R1 and R2 to support

2 MPLS headers, so we will change the

MPLS MTU to 1508 on their Fast Ethernetinterfaces

Verify the change using the

show mpls interfaces interface detail

command used



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MPLS Lab

As you can see, GNS3 running Dynagen

and Dynamips is a very useful tool

As you can also see, MPLS is easy to

setup

Copyright 2011 Kenneth M Chipps Ph D www chipps com 57

mpls lab with basic configuration

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