Using a Top Down Network Design Methodology

The world we've made as a result of the level of thinking we have done thus far creates problems that we cannot solve at the same level at which we created them. To paraphrase Einstein, networking professionals have the ability to create networks that are so complex that when problems arise they can't be solved using the same sort of thinking that was used to create the networks. Add to this the fact that each upgrade, patch, and modification to a network can also be created using complex and...

Mesh Versus Hierarchical Mesh Topologies

Partial And Full Mesh Topology

Network designers often recommend a mesh topology to meet availability requirements. In a full-mesh topology, every router or switch is connected to every other router or switch. A full-mesh network provides complete redundancy, and offers good performance because there is just a single-link delay between any two sites. A partial-mesh network has fewer connections. To reach another router or switch in a partial-mesh network might require traversing intermediate links, as shown in Figure 5-3....

Identifying the Scope of a Network Design Project

One of the first steps in starting a network design project is to determine its scope. Some of the most common network design projects these days are small in scope for example, projects to allow a few people in a sales office to access the enterprise network via a VPN. On the other hand, some design projects are large in scope. Ask your customer to help you understand if the design is for a single network segment, a set of LANs, a set of WAN or remote-access networks, or the entire enterprise...

Optimum Network Utilization

Network utilization is a measurement of how much bandwidth is used during a specific time period. Utilization is commonly specified as a percentage of capacity. For example, a network-monitoring tool might state that network utilization on an Ethernet segment is 30 percent, meaning that 30 percent of the capacity is in use. Network analysis tools use varying methods for measuring bandwidth usage and averaging the usage over elapsed time. Usage can be averaged every millisecond, every second,...

Making Network Design Tradeoffs

Despite what politicians tell us about state and federal budgets during an election year, in the real world meeting goals requires making tradeoffs. This section describes some typical network design tradeoffs. To meet high expectations for availability, redundant components are often necessary, which raises the cost of a network implementation. To meet rigorous performance requirements, high-cost circuits and equipment are required. To enforce strict security policies, expensive monitoring...

Tools for Developing Network Maps

Simple Network Diagram From Dmarcation

Many customers can't provide detailed and up-to-date maps of the existing network. In many cases, you need to develop the maps yourself. Companies that are constantly working in fire-fighting mode don't have time to proactively document the existing network. To develop a network drawing, you should invest in a good network-diagramming tool. You can use Cisco Works to map a network and collect other types of network audit information, including hardware and software versions, configurations, and...

Characterizing Types of Traffic Flow for New Network Applications

As mentioned, a network flow can be characterized by its direction and symmetry. Direction specifies whether data travels in both directions or in just one direction. Direction also specifies the path that a flow takes as it travels from source to destination through an internetwork. Symmetry describes whether the flow tends to have higher performance or QoS requirements in one direction than the other direction. Many network applications have different requirements in each direction. Some data...

Meeting Security Goals with Firewall Topologies

Dmz Topology

A firewall is a system or combination of systems that enforces a boundary between two or more networks. A firewall can be a router with access control lists (ACLs), a dedicated hardware box, or software running on a PC or UNIX system. A firewall should be placed in the network topology so that all traffic from outside the protected network must pass through the firewall. A security policy specifies which traffic is authorized to pass through the firewall. Firewalls are especially important at...

Multihoming the Internet Connection

The generic meaning of multihoming is to provide more than one connection for a system to access and offer network services. The term multihoming is used in many specific ways also. A server, for example, is said to be multihomed if it has more than one network layer address. Content delivery networks can multihome application layer data and services. The term multihoming is increasingly being used to refer to the practice of providing an enterprise network more than one entry into the...