II'III'DUUBIIOI'I Consider a group of companies that are managed by a single administrative body at the higher level {business and policy matters), and each company is separately administered at production or service level. The group policy is that each company will collaborate with the member companies in relevant business endeavours, while each company also will have autonomy to take its own operational and managerial decisions for better productivity and service efciency. Group management is taking steps to enforce IT enabled production and service delivery in all member companies. Some member companies have branches in distant locations while some companies are located in cities. Due to the above business model, Head of IT of each company is tasked with the designing of their IT infrastructure to facilitate internal operations as well as group collaborations. In 3 years, time. group management wants paperless offices within the group. In few months time, no additional telephone connections will be allowed, and all voice communications need to be v'olP based, using the IT infrastmcture of the group. Although intercompany connectivity is achieved using third party telecommunication providers, condentiality of data transfer needs to be ensured. City based companies or branches are to be connected through fibre links of Metropolitan Area Networks, while the others located elsewhere will use any reliable communication facility available in the region through a service provider. In either case, the policy is to use v'PNs. Each company has a main router, several switches depending on the size of the network and the required number of subnets, and few other routers if the company has branches. Depending on the size of a branch {if any), a branch may have a router and some switches to form the internal network. As at now, RIP is used as the routing protocol in all companies. Few static routes are also used. Ivlain two routers of the group head office have been used to connect to the Internet, and these two routers connect to the same cluster of routers at the ISP' end. These two routers are configured with load balancing to manage the traffic to and from the Internet. All internal networks are configured using private IP addresses. Ivlain two routers and the servers in the Group Head Office DeMilitarised Zone (DMZ) have public IP addresses. This DMZ hosts necessary NDS servers, proxies, mail relays, etc