MPLS Exam Cram

This is the start of notes on my cramming for the MPLS exam. It will consist of new or interesting MPLS information that I need to commit to memory.

• Multiple labels can be inserted, and the bottom-of-stack bit is set on the last label
• Labels consist of a 20 bit label, 3 bit experimental field, 1 bit bottom-of-stack indicator, and 8 bit TTL
• Ethertypes: 0x0800 is IP, 0x8847 is unicast with at least one label, 0x8848 is multicast with at least one label
• More than one label is used for VPNs and TE
• An LSR can push, swap, or pop labels
• MPLS is split into the control plane and data plane
• FEC: Packets forwarded based upon a common characteristic
• For Unicast IP Routing, an IP routing protocol and a Label distribution protocol are required
• Label distribution protocols match labels with networks
• FEC is the destination network
• PIM can be used for multicast, and the FEC is the destination multicast address
• TE requires OSPF or IS-IS with extensions
  
• RSVP or CR-LDP establishes tunnels and propagates labels
• With QoS, the FEC is the destination network and CoS
• In VPNs, two labels are used: Top points to egress router, second points to the outgoing interface on the egress router, or a routing table
  
• FEC is the site descriptor or VPN routing table