Designing Enterprise Campus Networks © 2004 Cisco Systems, Inc. All rights reserved. Designing the Campus Infrastructure ARCH v1.22-1

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Defining Logical Network Segments VLANs –Used to segment traffic –Usually defined by departments or organizational units –Can be defined by application (data, voice, and video) Separate, flat networks –Used for very small networks

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Avoid Campus-Wide VLANs A campus-wide VLAN: Creates large and overlapping spanning-tree domains Propagates problems (potential failure domain) Slows convergence Modern routers are not network bottlenecks.

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v One-VLAN-per-Switch Access Layer Model

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Unique VLANs per Switch

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v VLANs Spanning Multiple Access Switches

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Transmission Media Characteristics DistanceSpeedPriceTypical Uses Twisted Pair Important Up to 1000 Mbps (Gigabit Ethernet up to 100 m) LowBuilding Access Multimode Fiber Up to 2 km (Fast Ethernet) Up to 550 m (Gigabit Ethernet) Up to 1 GbpsModerate Building Distribution Campus Backbone Single- Mode Fiber Up to 40 km (Fast Ethernet) Up to 90 km (Gigabit Ethernet) 1, 10 Gbps or higher High Building Distribution Campus Backbone

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Data Link Protocol Characteristics SpeedPriceTypical Uses Ethernet 10 MbpsVery lowBuilding Access Fast Ethernet 100 Mbps Low Building Access Building Distribution Gigabit Ethernet 1000 Mbps Moderate Building Distribution Campus Backbone

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Long-Range Ethernet Characteristics Speed: 5 to 15 Mbps Price: High Typical uses: Campus Backbone

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Example: Transmission Media and Data Link Protocol Selection

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Selecting a Physical Network Segmentation Strategy Broadcast domains Use multilayer switching in a structured design to reduce the scope of broadcast domains. Failure domains Restrict the size of a failure domain to a single Layer 2 wiring-closet switch, if possible. Policy domains Define policy with access control lists that apply to an IP subnet.

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Implementing Spanning-Tree Protocol Select a spanning-tree implementation: –Spanning Tree Protocol (802.1D) Per-VLAN Spanning Tree Plus (PVST+) –Rapid Spanning Tree Protocol (802.1w) Multiple Spanning Tree (802.1s) Avoid Layer 2 loops and let Layer 3 protocols handle load balancing and redundancy. Keep the spanning-tree domain as simple as possible. Ensure that all links connecting backbone switches are routed links, not VLAN trunks. Use multilayer switching to reduce the scope of spanning-tree domains. Do not disable STP; keep it enabled just in case.

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Data Link Layer and Multilayer Switching Characteristics Data link layer switching supports simple, flat networks. Multilayer switching is useful in hierarchical networks that require complex routing. Multilayer switching offers advantages of equal cost routing, fast reconvergence, load balancing, and scalability. CostComplexityVersatilityTypical Uses Data Link Switching ModerateSimplerLess versatile Building Access Campus Backbone Multilayer Switching Expensive More complexMore versatile Building Distribution Campus Backbone

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Small Campus Network Collapse the Campus Backbone and Building Distribution submodules in the Campus Backbone submodule. Scale up to several Building Access switches.

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Medium Campus Design

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Multilayer Switched Campus Backbone

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Large-Scale Multilayer Switched Campus Backbone

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Question for Discussion What happens if you collapse the Building Access, Building Distribution, and Campus Backbone layers into one in terms of: Cost? Performance? Scalability? Availability?

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Selecting Hardware and Software

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Identifying an IP Addressing Strategy Determine the size of the network. How big is the network? How many locations are in the network and what are their sizes?

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Identifying an IP Addressing Strategy (Cont.) Determine if you need private or public addresses. –Are private, public, or both address types required? –What class of addresses and how many networks can be obtained from the public number authority? –How many end systems need access to the public network only? –How many end systems need to be visible to the public network also? –How and where will you cross the boundaries between the private and public addresses? Determine how to implement the IP addressing hierarchy. –Is hierarchy needed within the IP addressing plan? –What are the criteria to divide the network into route summarization groups?

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Mapping Layer 2 VLANs to Layer 3 Subnets Map Layer 2 domains to a Layer 3 subnet with an understandable VLAN to IP subnet numbering scheme. For example, data VLAN 20 and Voice VLAN 120 in Building 1 can correspond to x/24 and x/24. A good addressing scheme helps route summarization and eases troubleshooting.

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Static Routing Versus Dynamic Routing Use static routing in: Stub networks Smaller, nonexpanding networks Networks that require dial-on-demand routing Use dynamic routing in: Larger, expanding networks

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Routing Protocol Considerations SummarizationFlat Multiaccess (LAN) Point-to- Point Point-to- Multipoint (Frame Relay) RIP XXX IGRP XXX EIGRP XXXX OSPF XXXX IS-IS XXX

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Example: Small Enterprise Design

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Example: Medium Enterprise Design

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Example: Large Enterprise Design

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Summary Once you identify the application and data needs for an enterprise, you are ready to begin the logical network design by selecting logical network segments and the method you will implement to create logical network segments. The physical network design identifies the Layer 1 (physical) and Layer 2 (data link and spanning- tree) implementations for the enterprise network. The Enterprise Composite Network Model combines data link layer switching with multilayer switching to achieve robust, highly available campus networks.

© 2004 Cisco Systems, Inc. All rights reserved. ARCH v Summary (Cont.) The next step in the campus network design methodology requires that you select the Cisco hardware and software to implement at each location on the network. An effective IP addressing scheme is critical to the success and scalability of the network. The decision about which routing protocols to implement is based on the design goals and the physical topology of the network and the configuration of links for remote sites. Small, medium, and large campus networks use the Campus Infrastructure model applied to specific situations.