MPLS (1) - Multi-Protocol Label Switching IK2211 Data Links...

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MPLS Multi-Protocol Label Switching IK2211 Data Links and Local Area Networks Markus Hidell KTH School of ICT
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Multi-Protocol Label Switching
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Background • In the late 1990s (1995-1997) several new techniques to simplify IP forwarding appeared • Basic idea was to combine IP routing protocols with a forwarding algorithm based on a header with fixed length label instead of the longest prefix match on the destination IP address in the IP header • This resulted in an IETF standardization work, called MPLS (Multi-Protocol Label Switching) – Lots of RFCs regarding MPLS (overview in RFC 3031) • At the time these techniques were introduced there was a lot of debate regarding IP versus ATM, the label switching techniques were attempts to marry ATM cell forwarding with IP routing protocols
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MPLS Advantages Originally, it was claimed that label switching routers (LSRs) would be much faster thanks to simplified forwarding (fixed size label versus ”longest prefix match”) Performance argument may not be valid anymore, but • Label switching makes it possible to make forwarding decisions based on more complex criterias than IP dst address, but still keeping a simple lookup – New routing services, same forwarding paradigm •L a b e l s w i t c h i n g c a n b e u s ed for traffic engineering – Route control • Label switching can be used to support VPNs
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Forwarding Equivalence Class (FEC) Think of procedures used by the forwarding component as a way of partitioning the set of all possible packets a router can forward into a finite number of disjoint subsets. • Such a subset is referred to as an FEC • MPLS makes forwarding decision based on FEC belonging (labeling) • Mapping between information in the packet headers and the entries in the forwarding table is many-to-one (grouping of packets) •E x a m p l e : – A set of unicast packets whose IP address matches a certain prefix and whose ToS bits are the same •F E C c a n b e o f – Coarse granularity (essential for scalability) – Fine granularity (needed for flexibility)
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Control and Data Planes Control Plane (Binding Layer) Data Plane (Forwarding Layer) LFIB LSR MPLS packet MPLS packet Label distribution Label distribution Control Plane (Routing Layer) Data Plane (Forwarding Layer) FIB Router IP packet IP packet OSPF IS-IS BGP OSPF IS-IS BGP
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MPLS Forwarding • Label applied at ingress LSR—label is bound to an FEC • Forwarding based on label in MPLS cloud (transit LSRs) • Label removed at egress LSR Regular IP Network Regular IP Network MPLS cloud Label hdr Eth hdr IP hdr IP payload Add label Remove label
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This note was uploaded on 02/16/2011 for the course ICT 3 taught by Professor 3 during the Spring '11 term at Kungliga Tekniska högskolan.

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MPLS (1) - Multi-Protocol Label Switching IK2211 Data Links...

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