1. 12/9/2002Packet Rewrite Techniques1 Aparna Srikanta Swamy Reena Hans CS526 Semester Project 12/9/02

2. 12/9/2002Packet Rewrite Techniques2 Load Balancing Centralized. TCP router is used as a centralized switch to balance the load across a cluster. Content switch is another example. Drawback Single machine which has the responsibility of load balancing becomes a bottleneck at high loads.

3. 12/9/2002Packet Rewrite Techniques3 DPR An alternative decentralized approach is Distributed packet rewriting. Individual addresses of all machines in the cluster of web servers are published. Hence distributes the responsibility of re- routing amongst the web servers.

4. 12/9/2002Packet Rewrite Techniques4 Overview DPR is an IP level mechanism that equips a server with the ability to redirect an incoming connection to a different server in the cluster based on the very first SYN packet received from the client. Criteria for rerouting 1. Checking server’s MaxLoad. 2. Choosing another server with the lowest load.

5. 12/9/2002Packet Rewrite Techniques5 Functionality Routing Functionality in Kernel Space - ip_receive() function modified. Case 1: Packet contains a SYN. Case 2: Packet is not a SYN. Case 3: Packet contains an IP-IP.

6. 12/9/2002Packet Rewrite Techniques6 State Sharing Functionality in User Space. User Processes 1. Broadcast the local server’s own load periodically. 2. Waiting for the load of other servers. 3. Cleaning up of the load and the routing tables.

7. 12/9/2002Packet Rewrite Techniques7 Performance Evaluation SURGE - Scalable URL reference generator is used in 6 client machines. Web work load created. Surge was run in each client machine generating requests to three pentium class web servers(266Mhz, 128MB, 100Mbps Ethernet) running apache.

8. 12/9/2002Packet Rewrite Techniques8 Test Scenarios Four SURGE clients generated requests to Buick server, one to Brookline and one to Baystate. 3 scenarios tested No Load Balancing. Random Load Balancing. TCP Load Balancing.

9. 12/9/2002Packet Rewrite Techniques9 Test Results In random load balancing or TCP load Balancing – all the servers in the DPR cluster are serving approximately same number of connections. No Load Balancing, the machine with largest number of clients served maximum number of requests.

10. 12/9/2002Packet Rewrite Techniques10 Conclusions Routing power increases with the number of nodes. System is not completely disabled by the failure of any one node. More cost effective scaling of distributed servers.

11. 12/9/2002Packet Rewrite Techniques11 References Load Balancing a Cluster of Web Servers using Distributed Packet Rewriting by Luis Aversa and Azer Bestavros. http://cs.uccs.edu/~cs526/advancedCache/ipcc c00DistPktRewrite.pdf.ttp://cs.uccs.edu/~cs526/advancedCache/ipcc c00DistPktRewrite.pdf http://www.nmsl.cs.ucsb.edu/~ksarac/icnp/199 8/papers/1998-31.pdf