Atom-based Routing by gdf57j

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									        Atom-based Routing

Patrick Verkaik, Andre Broido, Young Hyun, kc claffy

            CAIDA / NLnet Labs / RIPE NCC

          http://www.caida.org/projects/routing/atoms/
Motivation
     Observation: many prefixes share AS path in all
  




     RouteViews / RIPE peers
     BGP policy atom: set of prefixes that share AS path
  




     Routed the same
  
Motivation
Fewer atoms than prefixes + atoms relatively stable:
      8 May 2003 RouteViews data:
   




       – around 33000 atoms
       – covering around 113000 prefixes
       – (15400 ASes)
      Stability over 8 hours:
   




      – 4.9% of atoms undergo prefix membership change
      – 2-3% of prefixes change atom membership
         (Tel Aviv University, 2002)
Apply to routing?
      Summarise prefixes of atom into one routed object
   




      Incorporate into BGP
   




Reduce number of routed objects in Default-Free Zone (DFZ):
      Shrink routing tables and forwarding tables
   




      Perform routing updates per atom, not per prefix
   




      Potentially improved convergence
   
Remainder of talk
     Architecture
  




     Incremental deployment
  




     Status and unresolved issues
  
Architecture
     Origination of atoms
  




     Overview of routing and forwarding
  




     Routing outside DFZ
  




     Routing inside DFZ
  




     Forwarding inside DFZ
  




     Forwarding outside DFZ
  
Architecture — Origination of atoms
     To be declared by origin ASes
  




     These ASes partition prefixes into atoms and announce
  




     Prefixes can be IPv4 or IPv6
  
Architecture — Example of declared atom
                AS                                    AS



                     P1
                                                      P3
                      P2                         P4        P5

                            P3
                       P4        P5


                                 AS


                                  P1
                                   P2

                                  P3
                             P4        P5



                      P1                    P3
                       P2              P4        P5


                            origin AS
Origin links and declared atoms
     Origin AS with neighbours to which an atom is announced
  




     – 40% of atoms have just one origin link (single-homed)
     – 37% of atoms have two origin links
     – the total is 24600 origin link sets
     – approximates the number of declared atoms
     – recall the number of full-AS-path atoms is 33000
Architecture — Overview of routing
Two functions:
      Atom routing
   




      – Atom is represented by an atom ID
      – Atom ID syntactically a prefix
         (unrelated to prefixes in atom)
      – Reason: BGP can route atom IDs
      Atom membership
   




                      




                                         ¢
      – Distributes atom ID     ¡




                                    prefix mapping
Membership technically not a routing protocol:
      No routing computations
   




      Location-independent (compare DNS)
   




      Future optimisation: separate protocol
   
Architecture — Overview of routing

                            AS


                        atom routes

                                       AS
         default−free
         zone         atom routes


                            AS




             AS                   AS

                  prefix routes
                   atom routes


                    origin AS
                                       (modified) BGP
Architecture — Overview of forwarding
                      sender        dest=A.B.C.D
                        AS

                                                         E.F.G.0/24    atom id

                                                         A.B.C.0/24
                                                         M.N.O.0/24 prefixes
                                                         I.J.K.0/24



           dest=E.F.G.H
                           dest=A.B.C.D

       default−free
          zone




                               AS



                                       De−encapsulation
                                                   destination AS



                                    A.B.C.D                   packet
                                                              encapsulated packet
Architecture — Overview of forwarding




       default−free
          zone




       sender
         AS           AS




                                     destination AS



                           A.B.C.D              packet
Architecture — Overview of forwarding
Comparing atom-based forwarding and MPLS:
      Atom ID similar to Forwarding Equivalence Class
   




      Encapsulation rather than label swapping
   




      MPLS not applied interdomain
   
Architecture — Routing outside DFZ



                default−free
                   zone             Announce atom         Announce prefixes
                                Withdraw               Withdraw
                                Announce     atom ID   Announce     prefixes
                                Membership prefixes    Membership "atomised"
atom routes                     attribute              attribute
        +
prefix routes        AS
                                    Withdraw atom         Withdraw prefixes
                                Withdraw     atom ID   Withdraw     prefixes
                                Announce               Announce
                                Membership             Membership
                  origin AS     attribute              attribute



       Atom announcement carries prefix membership in attribute
    




       Prefixes also routed separately
    
Architecture — Routing inside DFZ


           E
                                           E
               T               T
 E                                       AS

      AS
                                    default−free zone

                   T       T   AS                           transit router
                                                        T
                                                            edge router
                       E                                E
                                                            atom routes
                                                            prefix routes +
                                                            atom routes
Architecture — Forwarding inside DFZ



                                   E
                               T


   default−free zone                       transit router
                           T           T
                                           edge router
                                       E
                       E                   packet

                                           encapsulated packet
Architecture — Forwarding outside DFZ


              default−free
                 zone




     sender
       AS




                              packet

               origin AS      encapsulated packet
Incremental deployment
     Atomless prefixes
  




     ASes outside DFZ that are not atomised:
  




     – Nothing special happens between origin AS and DFZ
     – Forwarding is transparent
     – BGP attributes are optional transitive
     DFZ ASes that are not atomised.
  




     Solution: islands of atomised ASes
Incremental deployment — Islands
                      default−free zone




                      E
                                              AS

                                              atomised island

                  E
                                              transit router
                                          T
                                              edge router
                                          E
                                              other router
          E

              T   T

          E           E
Implementation
Status of implementation:
      Implemented previous architecture of atomised routing:
   




       – No notion of default-free zone
       – All routers prefix-aware
       – Implementing new architecture (fall 2003)
      In Zebra: free routing software (GNU license)
   




      Atoms declared manually in router configuration
   




      language (routemap)
TO DO
     Further analysis into the dynamics of atoms
  




     A DFZ membership protocol
  




     Look at non-AS path policies
  




     Declare atoms upstream from origin AS
  




     Failures that force atom re-declaration
  
Questions?
                         Acknowledgements

              Andrew Lange        Jeffrey Haas
              Andrew Partan       Maarten van Steen
               Bill Woodcock      Nevil Brownlee
            Bradley Huffaker      Mike Lloyd
                 CAIDA folks      Omer Ben-Shalom
         Cengiz Alaettinoglu      Pedro Roque Marques
          Daniel Karrenberg       Ronald van der Pol
                 Dave Meyer       Sean Finn
                  Evi Nemeth      Senthilkumar Ayyasamy
             Frances Brazier      Ted Lindgreen
           Frank Kastenholz       Teus Hagen
                Geoff Huston      Vijay Gill
             Henk Uijterwaal      Wytze van der Raay

             http://www.caida.org/projects/routing/atoms/
Architecture — Overview of forwarding
                      sender        dest=A.B.C.D
                        AS

                                                         E.F.G.0/24    atom id

                                                         A.B.C.0/24
                                                         M.N.O.0/24 prefixes
        Encapsulation
                                                         I.J.K.0/24



           dest=E.F.G.H
                           dest=A.B.C.D

       default−free
          zone




       sender
         AS                    AS



                                       De−encapsulation
                                                   destination AS



                                    A.B.C.D                   packet
                                                              encapsulated packet

								
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