- Multiprotocol Label Switching
- RFC3031
- Multiprotocol
- Can transport different payloads
- Layer 2 Payloads
- Ethernet, Frame Relay, ATM, PPP, HDLC, etc.
- Layer 3
- IPv4, IPv6, etc.
- Extensible for new future payloads
- Label Switching
- Switches traffic between interfaces based on locally significant label values.
- Similar to legacy virtual circuit switching
- Frame Relay input/output DLCI
- ATM input/output VPI/VCI
- Why?
- Transparent tunneling over SP network
- BGP Free core
- Saves routing table space on Provider routers
- Offer L2/L3 VPN service to customers.
- No need for overlay VPN model
- Traffic Engineering
- Distribute load over underutilized links
- Give Bandwidth guarantees
- Route based on service type
- Detect and repair failures quickly
- Fast Reroute (FRR)
- Label format
- 4 byte header used to “switch” packets
- 20 bit label – locally significant
- 3 bit EXP – Class of Service
- S bit – Defines last label in label stack
- 8 bit TTL – TTL
- 4 byte header used to “switch” packets
- Labels
- MPLS labels are bound to FECs
- Forwarding equivalency class
- IPv4 or IPv6 for CCIE purposes.
- Binding between label and IP prefix.
- Router uses MPLS LFIB instead of IP routing table to switch traffic.
- Switching Logic
- If traffic comes in if1 with label X, send it out if2 with label Y
- MPLS labels are bound to FECs
- MPLS Device Roles
- Consists of three types of devices
- Customer Edge (CE)
- Provider Edge (PE)
- Provider (P)
- Consists of three types of devices
- CE
- Last hop device in customer’s network.
- Connects to provider’s network.
- Can be layer 2 or 3.
- Typically not aware any MPLS is running.
- Last hop device in customer’s network.
- PE
- Also called Label Edge Router (LER)
- Last hop device in provider’s network.
- Connects to CE and provider core devices.
- Performs both IP routing and MPLS lookups.
- Traffic from customer to core
- Receives unlabeled packets (e.g. IPv4/6)
- Adds one or more MPLS labels
- Forwards labeled packet to core
- Traffic from core to customer
- Receives MPLS labeled packets.
- Removes one or more MPLS labels.
- Forwards packet to customer.
- P
- Also called Label Switch Router (LSR)
- Core devices in provider’s network
- Connects to PEs and other P routers
- Switches traffic based ONLY on MPLS labels
- Operations
- PE and P routers perform three major functions:
- Label push
- Add a label to incoming
- label imposition
- Add a label to incoming
- Label Swap
- Replace the label on an incoming packet
- Label pop
- Remove the labelfrom an outgoing packet
- Label push
- PE and P routers perform three major functions:
- Label Distribution
- Advertised via LD protocol
- Label Distribution Protocol (LDP)
- Advertises labels for IGP learned routes.
- RFC 5036
- MP-BGP
- Advertises labels for BGP learned routes.
- RFC 3107
- RSVP
- Used for MPLS Traffic Engineering (MPLS TE)
- RFC 3209
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