Overlay Networking Srinivasan Seetharaman Fall 2006

NTG seminar – Fall 2006 Overlay Networks Overlay networks help overcome functionality limitations of the Internet by forming a virtual network on top of the IP network. Overlay nodes collaborate to offer multiple services: Multicast (Ex: ESM, Overcast) Alternate paths (Ex: RON, Detour, X-Bone, Brocade) Customized forwarding (Ex: I3, Scattercast) QoS (Ex: OverQoS, SON) Name resolution, Intelligent routing…

NTG seminar – Fall 2006 Overlay Networks (contd.) Typical features: Overlay routing is independent of IP layer routing (Possibly with functionality overlap) End-system overlays ( Ex: Skype ), or Service overlays ( Offer services to actual end-systems ) Each Overlay link is actually an IP route between the two overlay nodes Each Overlay path is comprised of one or more Overlay links, inline with a certain objective

NTG seminar – Fall 2006 Example: Latency-Optimized paths A A D D C C B B 50ms 20ms Relaying Potential for selfish behavior. Impact varies based on the percentage of overlay traffic scale of overlay networks

NTG seminar – Fall Overlay routes can violate native layer polices - [Srini ICNP06] 2. Extra load on native links causing bottleneck issues. Serious issue when native layer wants load balance. - [Srini Ongoing] 3. Failure detected by both layers and rerouted twice, with each rerouting disrupting the optimality of the previous. - [Srini Infocom06] What can go wrong? A A D D C C B B 20ms Relaying

NTG seminar – Fall Sub-optimal performance because of lack of cooperation. Potentially a chicken-and-egg problem - [Srini Hotnets05] 5. Topology (Nodes+Links) placement is tricky - [Jinliang Infocom06, Sridhar Ongoing, YongZhu Infocom06] 6. Overlay routing can clash with TCP congestion control - [Ruomei Ongoing] What can go wrong? (contd.) A A D D C C B B 20ms Relaying

NTG seminar – Fall BGP Policy Violations Example violation over Planetlab and its benefit 6.3ms lower latency = 10.48% gain Transit policy is violated in the above example. Harvard Univ pays its provider unnecessarily and unavoidably.

NTG seminar – Fall Dual Rerouting Consider a native link failure in CE Only overlay link AE is affected. The native path AE is rerouted over F (ACE → ACFDE) Native Failure Overlay recovery: 8 Overlay rerouting: 4 Original: 2 Native Rerouting: 2 Time ∞ Native Recovery Native Repair Cost A B C D F E H I G A E I G OVERLAY NATIVE 4

NTG seminar – Fall 2006 Reduce extra copies on some links No extra copies on each link Latency to reach C is less … If there were native layer support 4. ESM-Friendly Native Network D D B B New packet replication capability C C A A Similar in spirit to REUNITE, Packet reflection

NTG seminar – Fall The services listed earlier, viz. QoS, Multicast, resilience, intelligent routing, security  Improve performance of TCP using schemes like Overlay-TCP - [Pradnya Networking05]  Improve services offered at the native layer by deploying them at the overlay layer (Ex: Name resolution) - [Sridhar Ongoing]  Creating improved service-based architectures and end- system driven functionalities - Anyone interested? What can go right?

NTG seminar – Fall 2006 References Jinliang Fan, Mostafa Ammar, "Dynamic Reconfiguration of Service Overlay Networks," IEEE INFOCOM, [PDF]PDF Yong Zhu and M. Ammar, "Algorithms for assigning substrate network. resources to virtual network components," IEEE INFOCOM, [PDF]PDF Pradnya Karbhari, M.Ammar, E. Zegura, "Optimizing End-to-End Throughput for Data Transfers on an Overlay-TCP Path", IFIP Networking, [PS]PS S. Seetharaman and M. Ammar, "Characterizing and Mitigating Inter-domain Policy Violations in Overlay Routes," IEEE ICNP, [PDF]PDF S. Seetharaman and M. Ammar, "On the Interaction between Dynamic Routing in the Overlay and Native Layers," IEEE INFOCOM, [PDF]PDF S. Seetharaman and M. Ammar, "Overlay-Friendly Native Network: A Contradiction in Terms?," ACM HOTNETS IV, [PDF]PDF