APT Incremental Deployment

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					       APT Incremental Deployment

                               Presented by
                             Lixia Zhang



Dan Jen, Michael Meisel, Daniel Massey, Lan Wang, Beichuan Zhang, Lixia Zhang
         http://www.cs.ucla.edu/~meisel/draft-apt-incremental-00.txt

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        APT Incremental Deployment

                    APT Island 1          APT Island 2


                                                 ISP5
                   ISP1

                                   ISP3                   Site7
           Site1


                                   ISP4           Site6


   Expect a combination of APT capable regions and
    BGP only regions
   Must provide incentives for APT first movers
   Must provide backwards compatibility with BGP
                                                                  2
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                           Terminology

• APT AS
   – A transit AS that has deployed APT

• Non-APT AS
   – A transit AS that has not deployed APT

• APT Island
   – A topologically connected set of APT ASes
   – The smallest possible island is a single AS
   – The largest possible island is the entire transit core (if APT is fully deployed)

• Island Mapping Table
   – The full mapping table for a particular APT island
   – Each entry maps an edge network to their APT providers
   – Every APT AS in the island stores the full island mapping table

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       Benefits for a Single Island

                                APT Island 1


                         ISP1              ISP2


                Site1                                  Site4
                        Site2                  Site3


• Prefixes for Sites 1, 2, 3, and 4 removed from the
  island’s BGP tables
  – Potentially large reduction in BGP table size!
• Offer benefits on next slide to such customers
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Additional APT Deployment Benefits

• For edge networks with only APT providers
  – Provider-independent addressing
  – No forced renumbering
  – Explicit traffic engineering preferences
• No changes required in edge networks
  – APT is deployed entirely in transit networks
• But some cost to transit ASes
  – Management of APT and BGP
  – Additional complexity of APT/BGP interactions



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        APT and Non-APT Interaction:
           Non-APT to APT (1/2)

                              APT Island 1


                       ISP1              ISP2                ISP3


              Site1                                  Site4          Site5
                      Site2                  Site3



   How can Site5 reach Site1?
−   Site1’s prefix is in APT Island 1’s island mapping table
−   But Site5 and ISP3 don’t understand APT
−   ISP2 must announce Site1’s prefix to ISP3 via BGP
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    APT and Non-APT Interaction:
       Non-APT to APT (2/2)

                          APT Island 1


                   ISP1              ISP2                ISP3


          Site1                                  Site4          Site5
                  Site2                  Site3



• How Can Site5 reach Site1?
  – ISP2’s Default Mapper (DM) gets Site1’s mapping
  – ISP2’s DM announces all APT edges’ prefixes into BGP
  – ISP3 receives and propagates the routes via BGP
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     APT and Non-APT Interaction:
        APT to Non-APT (1/2)

                           APT Island 1


                    ISP1              ISP2                ISP3


           Site1                                  Site4          Site5
                   Site2                  Site3


• How can Site1 reach Site5?
 – Site1 routes packets through ISP1
 – But Site5 is not in the APT mapping table…


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     APT and Non-APT Interaction:
        APT to Non-APT (2/2)

                           APT Island 1


                    ISP1              ISP2                ISP3


           Site1                                  Site4          Site5
                   Site2                  Site3


• How can Site1 reach Site5?
 – Border routers and DMs in APT Island 1 still have BGP tables
   that store non-APT prefixes
 – ISP1 forwards packets to the BGP next hop

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Communication between APT Islands
              (1/2)
                      APT Island 1              APT Island 2


                                                        ISP5
                     ISP1

                        BGP routes       ISP3        BGP routes   Site7
             Site1
                            BGP routes          BGP routes


                                         ISP4            Site6

   How can Site1 and Site7 communicate?
    – Both Site1 and Site7 are connected to APT islands
    – The APT islands are not connected and don’t share mappings
    – ISP1 does not have an APT mapping table entry for Site7
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Communication between APT Islands
              (2/2)
                       APT Island 1              APT Island 2


                                                         ISP5
                      ISP1

                         BGP routes       ISP3        BGP routes   Site7
              Site1
                             BGP routes          BGP routes


                                          ISP4            Site6

   How can Site1 and Site7 communicate?
    – ISP3 has a BGP route to Site7
    – ISP1 learns a BGP route to Site7 from ISP3
    – ISP1 can route to Site7 using the BGP route
    – Note: ISP1 does not know or care that Site7 is in an APT island      11
                                                                            11
                       APT Islands

• APT ASes in the same island share the same island
  mapping table
  – APT ASes in different islands do not (for now)
• Topologically connected islands can merge
  – Their mapping tables merge
     • Mapping tables are only stored at default mappers
  – All BGP tables shrink
     • BGP tables are stored in most routers

• Future work
  – Can we allow topologically unconnected islands to merge?
     • All APT networks could share a mapping table, no separate islands

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            Inside an APT Island

                   APT Island 1                          Site5



            ISP1                             X           ISP3
                   X          X   ISP2
        X    DM                   DM     X



Site1
                                                 Site4
             ITR

• Nodes labeled “X” are border routers
• Nodes labeled “DM” are default mappers

                                                                 13
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                       ITR Lookups

                           APT Island 1                           Site5



                ISP1                                  X           ISP3
                          X           X   ISP2
          X      DM                          DM   X



Site1
                                                          Site4
                 ITR

• How does the ITR decide what to do with a packet?
   – We are currently finalizing this part
   – The following is our favorite scheme as of now
   – Note that this is different from our draft
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        Sending to Non-APT Networks

               BGP Table:
               Site5 prefix found
                                APT Island 1                          Site5



                  ISP1                                    X           ISP3
                               X           X   ISP2
D: Site5   X       DM                          DM     X



Site1
                                                              Site4
                   ITR

• Site1 to Site5
   – Site5 is not attached to an APT network
   – The ITR has a BGP route to Site5
   – Packets are simply routed via BGP (not tunneled)
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        Sending to Non-APT Networks

                            APT Island 1                          Site5


                 D: Site5
               ISP1                                   X           ISP3
                            X          X   ISP2
          X     DM                         DM     X



Site1
                                                          Site4
                ITR

• Site1 to Site5
   – Site5 is not attached to an APT network
   – The ITR has a BGP route to Site5
   – Packets are simply routed via BGP (not tunneled)
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        Sending to Non-APT Networks

                         APT Island 1                              Site5


                             D: Site5                  X
               ISP1      X              X   ISP2                   ISP3
          X     DM                          DM     X



Site1
                                                           Site4
                ITR

• Site1 to Site5
   – Site5 is not attached to an APT network
   – The ITR has a BGP route to Site5
   – Packets are simply routed via BGP (not tunneled)
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        Sending to Non-APT Networks

                         APT Island 1                              Site5


                                        D: Site5
               ISP1                                    X           ISP3
                         X          X      ISP2
          X     DM                          DM     X



Site1
                                                           Site4
                ITR

• Site1 to Site5
   – Site5 is not attached to an APT network
   – The ITR has a BGP route to Site5
   – Packets are simply routed via BGP (not tunneled)
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        Sending to Non-APT Networks

                         APT Island 1                               Site5

                                                       D: Site5
               ISP1                                X                ISP3
                         X          X   ISP2
          X     DM                      DM     X



Site1
                                                            Site4
                ITR

• Site1 to Site5
   – Site5 is not attached to an APT network
   – The ITR has a BGP route to Site5
   – Packets are simply routed via BGP (not tunneled)
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        Sending to Non-APT Networks

                         APT Island 1                  D: Site5   Site5



               ISP1                                X              ISP3
                         X          X   ISP2
          X     DM                      DM     X



Site1
                                                         Site4
                ITR

• Site1 to Site5
   – Site5 is not attached to an APT network
   – The ITR has a BGP route to Site5
   – Packets are simply routed via BGP (not tunneled)
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        ITR Lookups for APT-Only Sites

                BGP Table:
                No entry for Site4
                                 APT Island 1                          Site5



                   ISP1                                    X           ISP3
                                X           X   ISP2
 D: Site4   X       DM                          DM     X



Site1
                                                               Site4
                    ITR

• ITR receives a packet for Site4
   – First look in the BGP table
   – Site4 is only connected to the APT island, so ITRs in the
     island don’t keep Site4’s prefixes in their BGP tables
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        ITR Lookups for APT-Only Sites

                Mapping Cache:
                Hit? Encap for ETR
                Miss? Encap for DM Island 1
                                 APT                                 Site5



                   ISP1                                  X           ISP3
                                X         X   ISP2
 D: Site4   X       DM                        DM     X



Site1
                                                             Site4
                    ITR                        ETR

• ITR receives a packet for Site4
   – Next check mapping cache
   – On the event of a cache miss, use the DM
   – This is normal APT behavior
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        ITR Lookups for APT-Only Sites

                          APT Island 1                          Site5

               D: ETR D: Site4
               ISP1                                 X           ISP3
                         X           X   ISP2
           X   DM                        DM     X



Site1
                                                        Site4
                ITR                       ETR

• Assume there is a cache hit
   – Tunnel to the ETR


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        ITR Lookups for APT-Only Sites

                         APT Island 1                             Site5

                                D: ETR D: Site4
               ISP1                                   X           ISP3
                         X          X     ISP2
           X   DM                          DM     X



Site1
                                                          Site4
                ITR                         ETR

• Assume there is a cache hit
   – Tunnel to the ETR


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        ITR Lookups for APT-Only Sites

                         APT Island 1                             Site5



               ISP1                                X              ISP3
                         X          X   ISP2
           X   DM                       DM     X
                                                       D: Site4


Site1
                                                          Site4
                ITR                      ETR

• Assume there is a cache hit
   – Tunnel to the ETR


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  ITR Lookups for Sites Multihomed
   with APT and Non-APT Networks

                    APT Island 1                          Site5



            ISP1                              X           ISP3
                    X          X   ISP2
        X    DM                    DM     X



Site1
                                                  Site4
             ITR

• What if Site4 multihomes with ISP3?                     New Link




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  ITR Lookups for Sites Multihomed
   with APT and Non-APT Networks
                BGP RIB-In:
                Site4 via ISP3
                ...              APT Island 1                          Site5



                   ISP1                                    X           ISP3
                                 X          X   ISP2
 D: Site4   X       DM                          DM     X



Site1
                                                               Site4
                    ITR

• ITR receives a packet for Site4
   – Now ITRs in the island have a BGP route to Site4
   – But we don’t want ITRs to only use the route through ISP3…

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  ITR Lookups for Sites Multihomed
   with APT and Non-APT Networks
                 BGP RIB-In:
                 Site4 via ISP3
                 Site4 via APT       APT Island 1                                           Site5



                     ISP1                                                  X                ISP3
                                    X           X          ISP2
 D: Site4    X         DM                                   DM         X



Site1
                                                                                    Site4
                       ITR

• Recall: DM generates BGP announcements for all prefixes
  in the mapping table
   – Special tag for sites multihomed with APT and non-APT nets
   – ITRs store these in their RIB-In
        • But still drop BGP routes for APT-only sites, which use a different tag                   28
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  ITR Lookups for Sites Multihomed
   with APT and Non-APT Networks
                BGP RIB-In:
                Site4 via ISP3
                Site4 via APT    APT Island 1                          Site5



                   ISP1                                    X           ISP3
                                 X          X   ISP2
 D: Site4   X       DM                          DM     X



Site1
                                                               Site4
                    ITR

• If the ISP3 BGP route is preferred
   – Forward using BGP table
• If the APT BGP route is preferred
   – Normal APT behavior                                                       29
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        ITR Lookups for Partial APT
                Networks

                                           APT Island 1



                      DM
               ISP1                                                X
                               X            X         ISP2
          X                X                              DM   X



Site1
                                   Site2                               Site4


• What if ISP1 wants to only partially deploy APT?
   – Now Site1 is a non-APT site
   – Site2 and Site4 are APT-only sites

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        ITR Lookups for Partial APT
                Networks

                                           APT Island 1



                      DM
               ISP1                                                X
                               X            X         ISP2
          X                X                              DM   X



Site1
                                   Site2                               Site4


• What if ISP1 wants to only partially deploy APT?
   – Even inside APT islands, we don’t tunnel packets destined
     for non-APT networks
   – Treat Site1 just like any other non-APT network
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               Thank You!

• Questions?




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