MPLS ( multi-protocol Label Switching) is a protocol which works on Label and not on traditional IP network and also works on Layer 2.5 at OSI Model. It is a WAN technologies which is used to connect remote offices with HO via Fiber connectivity. It uses a secure tunnel called VPN tunnel to established connection between two branches.
What is MPLS technology
It is a Routing technique for WAN to connect remote locations based on Labels rather than Network address. It Push SWAP and POP the Label from PE to CE. It operates at the data layer and network layer of the OSI model, that’s why its also called Layer 2.5 level.
Below are some key features :
- Label Switching : As above mentioned It uses Label instead of traditional IP routing and it determine the traffic based on Label. The Label are attached by PE or ingress router and P router will forward the packet based on Labels.
- Virtual Private Network ( VPN) : It provide a feature called VPN, where multiple customer network are separately logically and also provide security as its creates VPN tunnel end to end.
- Quality of Services (QOS) : It provide Quality of services by enabling prioritization and differentiation of traffic based on service level agreements.
- It also provide flexibility, Scalability and Efficiency in the network by reducing the complex routing configuration and follows Labelling mechanism.
Multi-protocol:
As this word is self-explanatory that this technology runs with any protocol.
Label Switching: Like other routing protocol it does look Packet or Frames, its forwards the traffic based on Label. It attaches the Label (PUSH), Replace the Label (SWAP) and Remove the Label (POP).
Key Points:
- It is depends on CEF. First CEF will run then MPLS will work.
- There are Label Lookup instead of IP Lookup.
- Use LDP / TDP (Label Distribution Protocol / TAG Distribution Protocol)
- It works on 2.5 at OSI Layer
Why 2.5 Layer
| 1.1.1.1 | 20 bit MPLS Label | MAC address |
| L3 | 2.5 | L2 |
As MPLS labels inserts in between of Layer-3 and Layer-2. so its called Layer 2.5 protocol.
MPLS Label Format:
It uses a 32-bit label field that contains the following information:
- 20-bit label
- 3-bit experimental field (QOS)
- 1-bit bottom-of-stack indicator ( it indicates that this is last Label)
- 8-bit time-to-live field (TTL)
Traffic flow mechanism
CE— Customer Edge-–First router which is connect to Provider for network, but it will not run on this router.
PE— Provider Edge–– it also called Ingress Label Switch Router and add (PUSH) the labels to traffic received from CE and Egress Label Switch Router where it Remove (POP) the label before sending them to CE.
P- Provider Router which forward traffic based on labels to next P router or Egress PE.
LSR– Label Switch Router— Routers where MPLS is run and they Swap the Labels.
LSP– Label Switch Path– the path which labelled packet will take to travel the traffic.
LDP– Label Distribution Protocol— Its assign the Label and forwarding the Label to other neighbours.
LLR–Labral Label Retention–MPLS Label reaches to all neighbour via IP unicast, is called LLR.
If user 1.1.1.1 wants to reach 2.2.2.2 and we need to run any IGP between end user network to CE1 and will create a header to add IGP information and IGP Best path.
Once CE1 forward MPLS header to PE1, it will add an action called PUSH. Once Header will create then MPLS router will not see the IP details only Label information will be checked.
After Label reaches to PE1, it will send to P router. P router will SWAP the Labels and it reaches to CE2 and CE2 will POP (Remove) the Label and forward the traffic to 2.2.2.2 based IGP best path route.
MPLS Data and Control Plane
| Control Plane | Data Plane |
| IGP, EGP, LDP, CEF | LFIB,Adjancies, ARP Table, Forwarding Table |
IGP— Interior Gateway Protocol (RIP, OSPF, IS-IS etc)
EGP ( Exterior Gateway Protocol (BGP)
LDP— Label Distribution Protocol
CEF— Cisco Express Forwarding– Before run MPLS need to enable CEF. CEF maintain FIB ( Forwarding Information Base) table which contain all Routing information.
There are two Table called LIB and LFIB
LIB– Label Information Base— Contains all Label information with FIB details.
LFIB- Label Forwarding Interface Base— Contains all Adjancies details.
MPLS doesn’t have any best path selection Algorithm, its totally depends on Routing protocols.
To enable LDP we need to run “ MPLS IP” and LDP will run.
LDP will send hello to neighbours devices on UDP port 646 with Multicast IP 224.0.0.2 and share update on port 646 with unicast.
What is use of TTL in MPLS
When first IP header comes on Ingress Router CE-1. it will add label which doesn’t contain any TTL value and if IP TTL is not there then Loop Avoidance will not work. So Label header copy IP TTL value in his label header and use it for Loop Avoidance and egress router will remove that label header and then original IP TTL value will forwarded on client end or distribution router.
What is Benefit of MPLS
The Main use or benefits of MPLS are:
- Improve network Performance: Increase network performance by adding Labelling in the network packet with less latency.
- Quality of Services (QOS): Implementation of QOS over MPLS to prioritize the real time application like Voice & Video.
- Traffic Engineering : Network administrators can optimize network performance and prevent congestion.
- Secure Connectivity: VPN over MPLS will provide end to end secure connectivity.
- Cost-Effectiveness : It is cost effective solution to connect multiple remote location on WAN.
FAQ
Q: What is MPLS?
A: MPLS stands for Multi-protocol Label Switching. It is a Routing technique for WAN to connect remote locations based on Labels rather than Network address. It Push SWAP and POP the Lable from PE to CE.
Q: How does MPLS work?
A: It assigned a Lable to identify the shortest path in the network to reach destination rather than network address. These Lable has been PUSH, SWAP and POP at every next hope.
Q: What are the benefits of using MPLS?
A: Benefits are including improve network Performance, Quality of Services (QOS), Traffic Engneering, Secure Connectivity, Cost-Effectiveness.
Q: What are the different components of an MPLS network?
A: It includes, CE-Customer Edge, PE- Provider Edge, P- Provider Router, Label Edge Routers (LERs), Label Switch Routers (LSRs), LSR- Label Switch Router, and Label Distribution Protocol (LDP).
Q: What is a Label Edge Router (LER)?
A: A Label Edge Router (LER) is the point where lables are start assigning and removing at entry and exit point.
Q: What is a Label Switch Router (LSR)?
A: Label Switch Router (LSR) is a Routers where MPLS Lable has been Push, SWAP & POP.
Q: What is Label Distribution Protocol (LDP)?
A: Label Distribution Protocol (LDP) is a protocol which is used to assign the Label and forwarding the Label to other neighbour.
- What is Labral Label Retention (LLR) ?
- MPLS Label reaches to all neighbour via IP unicast, is called LLR.
Q: What is MPLS VPN?
A: It is a virtual private network (VPN) that uses to securely connect remote location via secure Tunnel .
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