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| 1.0.-
Introduction about MPLS |
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| Having an IP domain like this: |
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| R1 and R6 are called edge routers; they are
located just in the frontier of the IP domain. R2, R3,
R4 and R5 are called
core routers; they do not communicate directly with the external world but
through the edge routers. |
| How to convert this IP domain to a MPLS domain? |
| Let's start naming the edge routers as LER
(Label Edge Router) and the core routers as LSR (Label Switch Router); for
now is just a way of naming. Later on we will find naturally and very
descriptive these funny names. |
| What work each of these routers has to do? LER
converts IP packets into MPLS packets when they are entering the domain, and
when leaving, it converts them back from MPLS packets to IP packets.
LSR
should forward MPLS packets following some instructions contained in one table
installed on it. Based on some information contained in the MPLS
packet, called Label, it selects a register from its installed table, and
following instructions given in this register, it forwards ahead the packet.
Next figures explain this better: |
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| LER receives an IP packet; then applying some
internal process, it converts the packet in one MPLS packet and forward it
into the MPLS domain. |
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| LSR seems to have a more complicated work. It
receives the MPLS packet, inspecting it to extract the information it
requires to enter in the internal table. Having this information, which is
called a label, it enters in the table with this value (imagine a
numbered key that open a box with instruction of what to do next). With the
value it can acceses the instructions required to know what to do with the
packet and how to forward it to the next selected interface. |
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