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Interdomain Routing

Verizon. AT&T. Comcast. Qwest. Interdomain Routing. Establish routes between autonomous systems (ASes). Currently done with the Border Gateway Protocol (BGP). Why is Interdomain Routing Hard?. Route choices are based on local policies . Autonomy: Policies are uncoordinated.

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Interdomain Routing

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  1. Verizon AT&T Comcast Qwest Interdomain Routing Establish routes between autonomous systems (ASes). Currently done with the Border Gateway Protocol (BGP).

  2. Why is Interdomain Routing Hard? • Route choices are based on local policies. • Autonomy: Policies are uncoordinated. • Expressiveness: Policies are complex. Always chooseshortest paths. Load-balance myoutgoing traffic. Verizon AT&T Comcast Qwest Avoid routes through AT&T ifat all possible. My link to UUNET is forbackup purposes only.

  3. BGP Route Processing (1) • The computation of a single node repeats the following: Choose“Best”Route UpdateRouting Table Send updatesto neighbors Receive routes from neighbors • Paths go through neighbors’ choices, which enforces consistency. • Decisions are made locally, which preserves autonomy. • Uncoordinated policies can induce protocol oscillations. (Much recent work addresses BGP convergence.) • Recently, private information, optimization, and incentive-compatibility have also been studied.

  4. BGP Route Processing (2) IP Forwarding Table Install forwarding entries for best routes Apply Import Policies Routing Table Best Route Selection Apply Export Policies Apply Policy = filter routes & tweak attributes Apply Policy = filter routes & tweak attributes Based on attribute values Transmit BGP updates Receive BGP updates Storageof routes Open-ended programming: constrained only by vendor configuration language

  5. Example: Convergence Prefer direct route to d 2 1 Prefer routes through 2 d

  6. Example: Oscillation Prefer routes through 1 BGP might oscillateforever between 1d, 2d and 12d, 21d 2 1 Prefer routes through 2 d

  7. Example: Convergence Prefer routes through 1 2 1 Prefer routes through 2 d

  8. Dispute Wheels Nodes ui, hub routes Ri, and spoke routes Qi. Each ui prefers RiQi+1 to Qi. “No dispute wheel” —> robust convergence

  9. Gao-Rexford Framework (1) Neighboring pairs of ASes have one of: • a customer-provider relationship(One node is purchasing connectivity fromthe other node.) • a peering relationship(Nodes have offered to carry each other’stransit traffic, often to shortcut a longer route.) peer providers customers peer

  10. Gao-Rexford Framework (2) • Global constraint: no customer-provider cycles • Local preference and scoping constraints, which are consistent with Internet economics: • Gao-Rexford conditions => BGP always converges [GR01] Preference Constraints Scoping Constraints . . . . R1 j provider k1 . . . . . . . . . . d . . . . i peer d i R2 . . . . . . m k2 k customer • If k1 and k2 are both customers, peers, or providers of i, then either ik1R1 orik2R2 can be more valued at i. • If one is a customer, prefer the route through it. If not, prefer the peer route. • Export customer routes to all neighbors and export all routes to customers. • Export peer and provider routes to all customers only.

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