Thursday, August 14, 2008

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

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