MPLS (Multi Protocol Label Switching)

Multiprotocol Label Switching (MPLS) is a mechanism in high-performance telecommunications networks that directs data from one network node to the next based on short path labels rather than long network addresses, avoiding complex lookups in a routing table. The labels identify virtual links (paths) between distant nodes rather than endpoints. MPLS can encapsulate packets of various network protocols. MPLS supports a range of access technologies, including T1/E1, ATM, Frame Relay, and DSL.

MPLS Label
00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Label EXP: Experimental (QoS and ECN) S: Bottom-of-Stack TTL: Time-to-Live

MPLS uses a 32-bit label field that contains this information

– 20 bit label

– 3 bit experimental field (Cisco QOS)

– 1 bit bottom of stack indicator

– 8 bit TTL field

Labels can also correspond to other Parameters

  • Layer 3 VPN
  • Layer 2 circuit
  • Outgoing interface on egress router
  • QoS
  • Source Address

MPLS was designed to support forwarding of non-IP protocols as well


  • LSR(Label Switch Router ro Provide(P) Router
  • Edge LSR (E-LSR) or Provider Edge(PE) Router
  • Ingress E-LSR (Enpose)
  • Egress E-LSR (Dispose)
  • Customer Edge (CE) Router
  • Customer (C) Router


MPLS Database: FIB   and LFIB



Cisco Routers can be configured to disable MPLS TTL Propagation

MPLS Control Plane

* Control plane protocol used for MPLS Label information


IOS Troubleshooting tools

show A snapshot of what is occurring to monitor status. The show commands enable you to detect neighbors, spot performance issues, and isolate problems.
ping Determine end-to-end connectivity and reachability.
traceroute Hop-by-hop approach to finding the problem.
log Monitor and view messages that record real-time events, such as errors, warnings, and state transitions.
debug Use for troubleshooting traffic flow or misconfigurations; not for normal daily operations.

CCIE v5 Routing and Switching

Topics Added to the CCIE Routing and Switching v5.0 Written Exam:
• Describe basic software architecture differences between IOS and IOS XE
• Identify Cisco Express Forwarding Concepts
• Explain General Network Challenges
• Explain IP, TCP and UDP Operations
• Describe Chassis Virtualization and Aggregation Technologies
• Explain PIM Snooping
• Describe WAN Rate-based Ethernet Circuits
• Describe BGP Fast Convergence Features
• ISIS (for IPv4 and IPv6)
• Describe Basic Layer 2 VPN – Wireline
• Describe Basic L2VPN – LAN Services
• Describe GET VPN
• Describe IPv6 Network Address Translation
Topics Added to the CCIE Routing and Switching v5.0 Written and Lab Exams:
• Use IOS Troubleshooting Tools
• Apply Troubleshooting Methodologies
• Interpret Packet Capture
• Implement and Troubleshoot Bidirectional Forwarding Detection
• Implement EIGRP (multi-address) Named Mode
• Implement, Troubleshoot and Optimize EIGRP and OSPF Convergence and Scalability
• Implement and Troubleshoot DMVPN (single hub)
• Implement and Troubleshoot IPsec with pre-shared key
• Implement and Troubleshoot IPv6 First Hop Security