Enterprise Campus: Layer 3 Routing Design Considerations
The hierarchal enterprise campus architecture can facilitate achieving more structured hierarchal Layer 3 routing design, which is the key to achieving routing scalability in large networks. This reduces, to a large extent, the number of Layer 3 nodes and adjacencies in any given routing domain within each tier of the hierarchal enterprise campus network 27.
In a typical hierarchal enterprise campus network, the distribution block (layer) is considered the demarcation point between Layer 2 and Layer 3 domains. This is where Layer 3 uplinks participate in the campus core routing, using either an interior routing protocol (IGP) or Border Gateway Protocol (BGP), which can help to interconnect multiple campus distribution blocks together for end-to-end IP connectivity.
By contrast, with the routed access design model, Layer 3 routing is extended to the access layer switches. Consequently, the selection of the routing protocol is important for a redundant and reliable IP/routing reachability within the campus, considering scalability and the ability of the network to grow with minimal changes and impact to the network and routing design. All the Layer 3 routing design considerations discussed in previous chapters must be considered when applying any routing protocol to a campus LAN. Figure 3-7 illustrates a typical ideal routing design that aligns the IGP design (Open Shortest Path First [OSPF]) with the enterprise campus hierarchal architecture, along with the different functional modules.
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Figure 3-7 Campus Network: Layer 3 Routing
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Figure 3-8 Campus Network: Layer 3 Design with WAN Core