MPLS Label - Header

The MPLS labels are advertised between routers so that they can build a label-to-label mapping.
These labels are attached to the IP packets, enabling the routers to forward the traffic by looking at the label and not the destination IP address. The packets are forwarded by label switching instead of by IP switching.

The MPLS label also called a shim header is 32bit (4 octets). Below is MPLS label looks like..

A MPLS label contains the following parts.

20-bit label value
3-bit experimental field
1-bit bottom-of-stack indicator
8-bit time-to-live filed

First 20 bit defines the original length of the actual label. Next 3-bit is experimental field which is used to copy QoS value from IP header like IP precedence or DSCP values. After that we have Bottom-of-stack value which defines weather the label is a last label. If it is set to 0 then its mean there are more labels and set as 1 defines that it’s a last label in a packet. Last field contains the 8-bit Time-to-live field which is same as IP Header time-to-live value and copied from IP header at PE router. We can also disable copying of TTL value from IP header to MPLS label.

KnowledgeNet MPLS Lab in GNS3

Dear Readers,

I am posting GNS3 Topology and lab config for Basic MPLS lab presented in Knowledge Net Student Guide 2.0. I am sure this will provide useful help to the poeples who are in the journery of learning MPLS and save lot of time in configuring basic IP configuration and to setup basic lab. This is full configured and fuctional lab by using IOS "c3640-jk9o3s-mz.124-16.bin"

Click the below "Show Config" link to see sample config of PE11 Router and get complete configuration with GNS3 topology file from " knowledgnet mpls lab.zip

Show Config /Hide Config

!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname PE11
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
memory-size iomem 5
!
!
ip cef
!
!
ip vrf cust-a
rd 1:10
route-target export 1:10
route-target import 1:10
!
ip vrf cust-b
rd 1:15
route-target export 1:15
route-target import 1:15
!
!
!
interface Loopback0
ip address 192.168.1.17 255.255.255.255
!
interface Serial0/0
ip address 192.168.1.49 255.255.255.240
mpls label protocol ldp
mpls ip
serial restart-delay 0
!
interface Serial0/1
ip vrf forwarding cust-a
ip address 150.1.1.18 255.255.255.240
serial restart-delay 0
!
interface Serial0/2
ip vrf forwarding cust-b
ip address 150.1.1.34 255.255.255.240
serial restart-delay 0
!
interface Serial0/3
no ip address
shutdown
serial restart-delay 0
!
router eigrp 10
network 150.1.0.0
network 192.168.1.0
no auto-summary
!
router rip
version 2
!
address-family ipv4 vrf cust-b
redistribute bgp 65001 metric transparent
network 150.1.0.0
no auto-summary
exit-address-family
!
address-family ipv4 vrf cust-a
redistribute bgp 65001 metric transparent
network 150.1.0.0
no auto-summary
exit-address-family
!
router bgp 65001
no synchronization
bgp log-neighbor-changes
neighbor 192.168.1.33 remote-as 65001
neighbor 192.168.1.33 update-source Loopback0
no auto-summary
!
address-family vpnv4
neighbor 192.168.1.33 activate
neighbor 192.168.1.33 send-community both
neighbor 192.168.1.33 next-hop-self
exit-address-family
!
address-family ipv4 vrf cust-b
redistribute static
no synchronization
exit-address-family
!
address-family ipv4 vrf cust-a
redistribute rip
no synchronization
exit-address-family
!
ip http server
no ip http secure-server
!
!
!
!
!
!
control-plane
!
!
!
!
!
!
!
!
!
!
line con 0
exec-timeout 0 0
line aux 0
line vty 0 4
login
!
!
end

Advantages of MPLS

· MPLS enables a single converged network to support both new and legacy services, creating an efficient migration path to an IP-based infrastructure. MPLS operates over both legacy (DS3, SONET) and new infrastructure (10/100/1000/10G Ethernet) and networks (IP, ATM, Frame Relay, Ethernet, and TDM).

· MPLS enables traffic engineering. Explicit traffic routing and engineering help squeeze more data into available bandwidth.

· MPLS supports the delivery of services with Quality of Service (QoS) guarantees. Packets can be marked for high quality, enabling providers to maintain a specified low end-to-end latency for voice and video.

· MPLS reduces router processing requirements, since routers simply forward packets based on fixed labels.

· MPLS provides the appropriate level of security to make IP as secure as Frame Relay in the WAN, while reducing the need for encryption on public IP networks.

· MPLS VPNs scale better than customer-based VPNs since they are provider-network-based, reducing the configuration and management requirements for the customer.

MPLS - Multi Protocol Label Switching

MPLS technology is around us since few years but the technology is awsome. The MPLS labels are advertised between routers so that they can build a label-to-label mapping. These labels are attached to the IP packets, enabling the routers to forward the traffic by looking at the label and not the destination IP address. The packets are forwarded by label switching instead of by IP switching.

The label switching technique is not new. Frame Relay and ATM use it to move frames or cells throughout a network. In Frame Relay, the frame can be any length, whereas in ATM, a fixed length cell consists of a header of 5 bytes and a payload of 48 bytes. The header of the ATM cell and the Frame Relay frame refer to the virtual circuit that the cell or frame resides on. The similarity between Frame Relay and ATM is that at each hop throughout the network, the "label" value in the header is changed. This is different from the forwarding of IP packets. When a router forwards an IP packet, it does not change a value that pertains to the destination of the packet; that is, it does not change the destination IP address of the packet. The fact that the
MPLS labels are used to forward the packets and no longer the destination IP address have led to the popularity of MPLS.