Document Managed by Network Architecture

Introduction

Rutgers University has recognized the strategic necessity of the network infrastructure in accomplishing its mission of teaching, research and outreach. Historically, the network was a research and collaboration aid, but over time virtually all facets of the University have come to rely on network access. Historically, there has been incomplete penetration of network infrastructure in numerous areas, but there is now a critical focus to accommodate the diverse networking needs of the University. The goal of the RUNet 2000 project will be to construct a flexible, fault tolerant network connecting all of Rutgers University.

Discussion

By definition, the design model is a loose set of requirements and goals intended to reduce the state space of solutions from which an implementation model can be developed. As such, there are no references to explicit bandwidth values, building boundaries, fiber limitations, or redundancy. These issues will be addressed as part of the implementation model. The design model does not constitute an implementation model.

The basic design consists of isolated trees connected at their root nodes and utilizing four elements: core, distribution, access and leaf nodes (see figure 1). The network design model is not based directly on the network fiber model, however, the connection of network elements using a tree topology is consistent with both the underlying fiber plant and the proposed routing protocol. Rutgers University will rely on the Open Shortest Path First (OSPF) routing protocol, which functions significantly better in tree like topologies.

Figure 1: Topological map of the design network representing core (C), distribution (D), access (A), and leaf (L) nodes.

The above indicates topological relationship between nodes consistent with the following rules:

• Core nodes are L3 devices representing the central network infrastructure. Policy enforcement does not take place at core nodes.
• The distribution nodes are L3 devices where policy enforcement may occur. Filtering is permitted to take place at either the L2/L3 transition, the L3/L2 transition, or both.
• The core and distribution nodes are the only L3 devices in the network.
• Core nodes are L3 neighbors to at least two other core nodes.
• Distribution nodes are L3 neighbors to at least one core node.
• Access nodes are L2 neighbors to at least one distribution node. Access nodes may not connect directly to core nodes.
• Leaf nodes are L2 neighbors to at least one access node. Leaf nodes may not connect directly to distribution nodes or core nodes.
• The bandwidth of a distribution node to its parent core node should be greater than or equal to the bandwidth of the largest individual link between it and its children access nodes.
• The network will not support non-IP protocols above the distribution router.

These policies are intended as design guidelines and what is not explicitly excluded, is permissible in subsequent implementation models. It should also be noted that an L2 connection may be point to point or take place through an L2 device (such as a switch). An L2 connection, by definition, precludes hardware address rewrites and decremented TTL. These take place at L3 nodes only. Further, the provisions pertaining to neighbor relationships, do not exclude the possibility for redundancy to exist in the implementation model. Redundancy is clearly possible within the constraints of this design model. The design goal of a maximum L3 distance of 3 segments between any host and the core is a practical minimum imposed by the restrictions on policy enforcement.

Conclusion

The network design model constitutes a flexible set of constraints that will govern the design of implementation models. Where inconsistencies are identified at a foundation level, they will be incorporated into a new network design model that is immediately propagated forward to succeeding implementation models. In this fashion, the redesign of the Rutgers network will proceed iteratively, ultimately converging on an overall model.