MPLS

MPLS Label Distribution Parameters

MPLS Label Distribution Parameter Options:

Label Space Options	Per-Interface	Per-Plaform
Label Distribution	Unsolicited downstream	Downstream-on-Demand
Label Allocation	Independent Control Mode	Ordered Control Mode
Label Retention	Liberal Label Retention	Conservative Label Retention

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Label Space Options

Per-Platform Labels

• LFIB: [Label | Action | Next Hop ]
• one label assigned to a destination network and announced to all neighbors
• locally unique, valid on all incoming interfaces
• smaller LFIB, FIB; faster label exchange
• less secure than per-interface labels; label-spoofing
• default in Frame-Mode MPLS

Per-Interface Labels

• LFIB:[IN intf | IN Label | NH intf | NH Label]
• one label for each destination, each device, each interface
• secure; prevents label-spoofing; labeled packets/ATM cells only accepted from interface where label is assigned
• default in Cell-Mode MPLS

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Label Distribution

Unsolicited Downstream

• label advertised to all neighbor LSRs, regardless of whether upstream or downstream
• Frame-Mode

Downstream-On-Demand

• label advertised only upon request of upstream LSR
• cell-mode

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Label Allocation 

Independent Control

• LSR can assign a label for a prefix w/o outgoing/downstream label
• for edge LSRs only (requires L3 capabilities)
• faster label propagation
• for unsolicited downstream / frame-mode

Ordered Control

• local label allocated and propagated only
• if exist(nexthop label) propagae/allocate label, else request label from nexthop
• for downstream-on-demand/cell-mode

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Label Retention

Liberal Label Retention

• all received label stored in LIB, even if not from next-hop LSR
• improves convergence speed; allows easy failover for link failures
• frame-mode

Conservative Label Retention

• only received labels from nexthop LSRs are  stored; others are ignored
• downstream-on-demand/cell-mode

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Standard Parameter Sets for Cisco Platforms

Parameter	Routers, frame interfaces	Routers, ATM interfaces	ATM switches
Label Space	per-platform	per-interface	per-interface
Label Distribution	unsolicited downstream	downstream-on-demand	downstream-on-demand
Label Allocation	independent control	independent control	ordered control
Label Retention	liberal label retention	conservative OR liberal	conservative