MPLS Operation

The following algorithm is carried out by the MPLS module:

Step 1: - Check which layer the packet is coming from
Alternative 1: From layer 3
    Step 1: Find and check the next hop of this packet
    Alternative 1: Next hop belongs to this MPLS cloud
        Step 1: Encapsulate the packet in an MPLS packet with
        IP_NATIVE_LABEL label
        Step 2: Send to the next hop
        Step 3: Return
    Alternative 2: Next hop does not belong to this MPLS cloud
        Step 1: Send the packet to the next hop
Alternative 2: From layer 2
    Step 1: Record the packet incoming interface
    Step 2: - Check if the packet is for this LSR
    Alternative 1: Yes
        Step 1: Check if the packet has label
        Alternative 1: Yes
            Step 1: Strip off all labels and send the packet to L3
            Step 2: Return
        Alternative 2: No
            Step 1: Send the packet to L3
            Step 2: Return
    Alternative 2: No
        Step 1: Continue to the next step
    Step 3: Check the packet type
    Alternative 1: The packet is native IP
        Step 1: Check the LSR type
        Alternative 1: The LSR is an Ingress Router
            Step 1: Look up LIB for outgoing label
            Alternative 1: Label cannot be found
                Step 1: Check if the label for this FEC is being requested
                Alternative 1: Yes
                    Step 1: Return
                Alternative 2: No
                    Step 1: Store the packet with FEC id
                    Step 2: Do request the signalling component
                    Step 3: Return
            Alternative 2: Label found
                Step 1: Carry out the label operation on the packet
                Step 2: Forward the packet to the outgoing interface found
                Step 3: Return
        Alternative 2: The LSR is not an Ingress Router
            Step 1: Print out the error
            Step 2: Delete the packet and return
    Alternative 2: The packet is MPLS
        Step 1: Check the LSR type
        Alternative 1: The LSR is an Egress Router
            Step 1: POP the top label
            Step 2: Forward the packet to the outgoing interface found
            Step 3: Return
        Alternative 2: The LSR is not an Egress Router
            Step 1: Look up LIB for outgoing label
            Alternative 1: Label cannot be found
                Step 1: Check if the label for this FEC is being requested
                Alternative 1: Yes
                    Step 1: Return
                Alternative 2: No
                    Step 1: Store the packet with FEC id
                    Step 2: Do request the signalling component
                    Step 3: Return
            Alternative 2: Label found
                Step 1: Carry out the label operation on the packet
                Step 2: Forward the packet to the outgoing interface found
                Step 3: Return
Step 2: Return

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