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CIS679: Anycast

CIS679: Anycast. Review of Last lecture Network-layer Anycast Single-path routing for anycast messages Application-layer anycast. Review of Last Lecture. Anycast motivation Anycast address Anycast membership management Anycast routing Multi-routing

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CIS679: Anycast

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  1. CIS679: Anycast • Review of Last lecture • Network-layer Anycast • Single-path routing for anycast messages • Application-layer anycast

  2. Review of Last Lecture • Anycast motivation • Anycast address • Anycast membership management • Anycast routing • Multi-routing • loop-free routing methods: SSPF, MIN-D, CBT and SBT • multiple path selection

  3. Single-Path Routing for Anycast Messages • GIA: Global IP-Anycast (GIA) by MIT • Anycast address • Anycast indicator + home domain + group_id • Anycast membership management -- IGMP

  4. Anycast Routing in GIA • Single-path routing • Discriminating different anycast groups • On demand routing: caching

  5. Summary of Network-layer Anycast • Multi-path/single-path routing • Trade-off: performance and scalability • Remaining Issues in Network-layer Anycast • Anycast flow • How to get multiple paths? • etc

  6. Application-layer Anycast • The basic scheme: Server selection • Advantages: • Easier to implement • Server load information can be used • Disadvantages: • Difficult to collect network information: distance, available bandwidth • Difficult to act as a tool to do load balance at network layer, such as supporting multicast

  7. Service Redirection • Most web sites have many servers • For scalability • To reduce traffic/network congestion problems in providing service • May be geographically distributed • For fault tolerance • How to direct users to one of the servers?

  8. DNS Aliasing • Advertise a single name for the service • Could have multiple servers (with different IP addresses) for the same service • When user contacts DNS resolver, name to IP address mapping done in round-robin fashion • Can distribute load among the servers

  9. Proxy of Servers: Magic Router • Works when the servers are all the same subnet • Advertise one front-end server’s address • This server looks at the packets and distributes to servers behind • Achieves good load balance

  10. Proxy: Magic Router • Not scalable, single point of failure, servers have to be localized • Magic router has look at every packet to and from the server • Magic router modifies addresses in both directions-transparent to users/servers • Works well for departmental servers

  11. Conclusion • Network-layer anycast • Application-layer anycast • Server selection • Service redirection • DNS aliasing • Proxy: magic router

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