Misc MPLS VPN Basics

MPLS notes for personal use

Switches locates the destination by comparing the mac address with the lookup table.

Routers locates the next hop by comparing the ip address with the routing table.

But MPLS routers locates the next hop by comparing the label id with the .......table.

Switches operate in Layer 2

Routers operate in Layer 3

MPLS operates in Layer 2.5

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Label format is for 32 bits.

20 bits for label id

3 bits for class of service

1 bit for stack point

8 bit for TTL

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When a packet enters into the first router of mpls cloud, that router is called as Ingress LER (LER stands for Label edge router. ingress stands for in-point). The LER inserts (PUSHES) the label into each frame. The Egress LER removes(POPs) the labels and send the packet outside mpls cloud

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Why MPLS needed for a customer?

It does Traffic Engineering

It gives QoS over IP

it creates a virtual private network.(vpn)

 

traffic isolation and differentiation is possible with less overhead

 

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When the traffic has a specific bandwidth requirements, atm or framerely WAS the option. In that PrivateVirtual Circuit (PVC)concept is there.

 

Customer can hide the ip address.

Customer can even use the private ip address. So that two more offices at different locations can be interconnected just like a private network.

Can get a constant speed which is needed for video,etc.

Encryption of packets can be done (it is optional)

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There are different types of vpn. IP based VPN, IPSec VPN or ATM

In ip, for each packet, router has to look into the routing table and take decisions. But in mpls, routing decisions are taken by control plane(ospf and lsr) and once a packet is reaching, simply forwarded by the data plane by looking into fib. so it is fast. there is no need of knowing the actual ip address of the packet. Not only ip, any other protocol also can be forwarded (that is why they called as multiprotcol)

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ospf fills the routing table. and ldp fills up the lip. dataplane just uses the lib. this method is almost harwire speed?

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fec?

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ce is customer edge router, pe is provider edge router, p is provider router or core router.

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anology: a person entering a campus. First check his requirement thoroughly and give him an id card. with his id card, he is able to move around easily inside the campus. difference is , id is swapped between any two check points.

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stack

s0 s0 s0 s1, here the first s0 is the top most label.

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Not only ip based, even If the customer end is atm or frame relay, then also mpls can be used

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mpls inserts a label called as shim label l2 and l3. so it is known as 2.5

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LER are also known as PE or Edge LSR. this is more sophisticated than LSR.

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MPLS routers use Label Forwarding Information Base (LFIB) instead of routing tables

 

What is Qos?

QoS means a certain guaranteed performance level of the network determined by certain metrics such as packet loss, latency and jitter

 

Normally ip is not worried about the specific bandwidth requirements of each user or importance of any traffic. It does routing based on best effort delivery. All users are equal for ip.

While ip is connectionless, we can say, mpls is connection oriented.

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swift disaster recovery via methods such as Fast Reroute (FRR). The traffic
is rerouted through backup lsp

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difference between qos and te?

qos is explained already. te is, suppose the link between a and b is broken, then immediately it is re routted via a to c then c to b. ????????

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vrf?

 

it is unique to each user. vrf is virtual routing and forwarding. so all other users using the mpls cloud are transparent because of vrf concept.

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