(a) Consider the layer-2 switch topology shown below. Switch A Port number 1 Host X 2 3 ? Host Y Switch B 4 Port number Time Sent Step by Device on Link 0 X X-A1 1 C 5 Assuming all switches start with empty switch-forwarding tables; Host X (with physical address X) sends a packet destined for Host Z. Enumerate in the style below, all packets sent across the network until the message arrives at Host Z. You may assume packet-processing, latency and transmission time are negligible. Additionally, indicate packets transmitted simultaneously. C7-Z Switch C 6 B X Port number Frame Source Destination X Z Destination Port Host Z Z (b) Enumerate in the style below, the forwarding table of Switch B at the end of Part (a). (c) Consider a layer-2 network consisting of S+1 switches, S directly attached to H hosts. Each host runs V virtual machines, each with a single address. S switches are connected using a star topology with a single switch C at the centre. Each host exchanges data with a selected and stable subset of other hosts. Estimate the worst case number of entries in the forwarding table for any typical switch S and the number of entries in the forwarding table for switch C. (d) Users of this cluster of machines complain of occasional misbehaviour attributed to network timeouts and network slowdown. Outline two plausible chains of events causing the problem. Describe two appropriate, cost-effective, strategies for overcoming the issues faced by the users. You may assume the switches are state-of-the-art and buying more hosts is not the answer. 1