ICNP 2006 Inter­domain Policy Violations in Overlay Routes Srinivasan Seetharaman, Mostafa Ammar Networking and Telecommunications Group College of Computing Georgia Institute of Technology

ICNP 2006 Typically in Service Overlays… Objective of overlay layer: Offer better latency routes to end-systems But, what is assumed here? The overlay traffic is just a small fraction Node at Harvard is capable of relaying overlay packets Colorado State Univ Harvard Univ Univ of NC 30 ms 24 ms 61 ms

ICNP 2006 Typically in Service Overlays… Objective of native layer: Enforce inter-domain policies and offer best-effort service Unhappy 1. Money 2. Load Client 1 Client 1 A Client 2 B Client 3 C Provider 1 Provider 2 Peer Legitimate native route Overlay route Valley-free violation

ICNP 2006 Outline We answer the following questions: What type of violations? How extensive are these violations? What benefit did overlays derive? What if ASes enforce policies? Framework for regaining routing advantage?

ICNP 2006 Focus What Inter-domain policies? Valley-free property (Thou shalt not transit for anyone but customers) Since unrelated AS is incurring expense Which overlay paths? Desirable multi-hop paths are our main concern Single hop paths are non-violating

ICNP 2006 Topology: 58 geographically distributed Planetlab nodes (Univ + Commercial). This yields 3306 overlay paths Measurement steps: 1. Determine AS path of each overlay link (Rockettrace / traceroute for hop list + IP  AS mapping) 2. Determine overlay path based on shortest path algo (For Cost = latency, 56.6% overlay paths prefer relaying) 3. AS relationships inferred using Gao’s algorithm See: Planetlab Overlay Measurements

ICNP 2006 I. Extent of Valley-free Violations A: Provider-AS-Provider (63.1%) B: Provider-AS-Peer (2.43%) Client 1 Provider 1 Client 2 Provider 2 Client 3 Peer Client 1 Provider 1 Client 2 Provider 2 Client 3 Peer

ICNP 2006 I. Extent of Valley-free Violations No violation if intermediate node is at a provider. In our dataset, 30.19% of paths had no violation C: Peer-AS-Provider (2.00%) D: Peer-AS-Peer (2.39%) Client 1 Provider 1 Client 2 Provider 2 Client 3 Peer Client 1 Provider 1 Client 2 Provider 2 Client 3 Peer

ICNP 2006 II. Benefit Derived Gain = Overlay link latency – Overlay path latency Overlay link latency

ICNP 2006 III. Enforcing Native Policies ASes may become aware of the negative impact of overlays and commence filtering Two modes for filtering objectionable traffic: 1. Blind filtering: Filter all overlay traffic at host AS 2. Policy-Aware Filtering: Filter only violating traffic (Ex: 30.19% of the relayed traffic is NOT blocked)

ICNP 2006 Penalty = Post-filtering Overlay path latency Best possible path latency III. Overlay Performance Diminishes Blind filtering Policy-aware filtering

ICNP 2006 Overlay service provider (OSP) shares some of the cost incurred by the native layer  We adopt two strategies: 1. Obtain transit permit: Lifetime fee of P i 2. Add new node: Lifetime fee of N i Cost-sharing approach IV. A Framework for Legitimizing Paths

ICNP 2006 With no filtering, 4 violating multi-hop overlap paths IV. Cost Sharing Approach Betweenness = 2 Cust-Prov relation Peering relation Overlay hosting AS

ICNP 2006 With filtering, we have no multi-hop paths Overlay routing is obviated and performance suffers IV. Cost Sharing Approach (contd.) Cust-Prov relation Peering relation Overlay hosting AS

ICNP 2006 After obtaining permit from AS 32 2 multi-hop overlap paths are permitted IV. Cost Sharing Approach (contd.) Transit Permit Cust-Prov relation Peering relation Overlay hosting AS

ICNP 2006 After adding new node to AS 23 2 reasonably good non-violating multi-hop overlap paths are permitted IV. Cost Sharing Approach (contd.) Add new node Cust-Prov relation Peering relation Overlay hosting AS

ICNP 2006 IV. Cost Sharing Problem For a certain budget, determine optimal set { N, P } that maximizes overall path gain where: N = Set of ASes where new nodes are placed P = Set of ASes being paid for permits Deriving optimal solution set is a hard problem. Hence…

ICNP 2006 IV. Greedy Heuristics Pay ASes along unrestricted best-gain path Obtain permits first from stub ASes that have high betweenness (# of overlay paths through the node) Next, add overlay nodes to upstream providers, starting with the overlay paths which achieve the highest gain

ICNP 2006 IV. Cost Sharing Results Let: Permit fee for each AS = P New node fee for each AS = N Add new nodePermit

ICNP 2006 Conclusions Overlay routing gains advantage by violating native layer policy. As overlay applications and overlay traffic surge, the native layer policy violations have a bigger impact User experience suffers drastically as more ASes deploy filtering mechanisms Our cost-sharing approach is a mutually agreeable solution to improve gain without causing violations.