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
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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
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Operation of MPLS
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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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What is Traffic Engineering
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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What is Traffic Engineering
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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What is Traffic Engineering
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 loopback 0 ip address 172.16.2.1 255.255.255.0
interface fastethernet 0/0
ip address 172.16.12.2 255.255.255.0 no shutdown
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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
network 172.16.0.0 interface fastethernet 0/0
mpls ip
exit end
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R3
enable
config t
interface loopback 0 ip address 172.16.3.1 255.255.255.0
interface serial 1/0
ip address 172.16.23.3 255.255.255.0 no shutdown
exitCopyright 2011 Kenneth M. Chipps Ph.D. www.chipps.com 31
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R3
router eigrp 1
no auto-summary
network 172.16.0.0 interface fastethernet 0/0
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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Verify MPLS Configuration
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Verify MPLS Configuration
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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Verify MPLS Configuration
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Verify MPLS Configuration
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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Verify MPLS Configuration
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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Verify MPLS Configuration
In a larger network, the way labels are
swapped is easier to see
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Verify MPLS Configuration
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Verify MPLS Configuration
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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Verify MPLS Configuration
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Verify MPLS Configuration
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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Verify MPLS Configuration
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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Verify MPLS Configuration
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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
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