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

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

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

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

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

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

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

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

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

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

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