CCNA-CH11.docx

The Need to Scale the Network Our digital world is changing. The ability to access the internet and the corporate network is no longer confined to physical offices, geographical locations, or time zones. In today's globalized workplace, employees can access resources from anywhere in the world and...

The Need to Scale the Network Our digital world is changing. The ability to access the internet and the corporate network is no longer confined to physical offices, geographical locations, or time zones. In today's globalized workplace, employees can access resources from anywhere in the world and information must be available at any time, and on any device. These requirements drive the need to build next-generation networks that are secure, reliable, and highly available. These next-generation networks must not only support current expectations and equipment but must also be able to integrate legacy platforms. Businesses increasingly rely on their network infrastructure to provide mission-critical services. As businesses grow and evolve, they hire more employees, open branch offices, and expand into global markets. These changes directly affect the requirements of a network which must be able to scale to meet the needs of business. Click Play in the figure to view an animation of a small network expanding into a larger network. An animation showing a small network adding a LAN as it increases the number of employees. Next, the company grows to multiple locations with multiple LANs in the same city. Then, the company grows into a multi-city enterprise and begins to hire teleworkers. Finally, the enterprise expands into other countries. A small, single location company. The company increases its number of employees. The company grows to multiple locations in the same city. The enterprise grows to multiple cities. The enterprise hires teleworkers. The enterprise expands to other countries.\ **Note**: Not all enterprise networks are international. The enterprise centralizes network management in a Network Operations Center (NOC). Internet **Orlando** **Boston** **Osaka** **New York** Network Operations Center A network must support the exchange of various types of network traffic, including data files, email, IP telephony, and video applications for multiple business units. All enterprise networks must be able to do the following: - - - - The LAN is the networking infrastructure that provides access to network communication services and resources for end users and devices. The end users and devices may be spread over a single floor or building. You create a campus network by interconnecting a group of LANs that are spread over a small geographic area. Campus network designs include small networks that use a single LAN switch, up to very large networks with thousands of connections. 11.1.3 Borderless Switched Networks With the increasing demands of the converged network, the network must be developed with an architectural approach that embeds intelligence, simplifies operations, and is scalable to meet future demands. One of the more recent developments in network design is the Cisco Borderless Network. The Cisco Borderless Network is a network architecture that combines innovation and design. It allows organizations to support a borderless network that can connect anyone, anywhere, anytime, on any device; securely, reliably, and seamlessly. This architecture is designed to address IT and business challenges, such as supporting the converged network and changing work patterns. The Cisco Borderless Network provides the framework to unify wired and wireless access, including policy, access control, and performance management across many different device types. Using this architecture, the borderless network, shown in the figure, is built on a hierarchical infrastructure of hardware that is scalable and resilient. The figure shows examples of a Cisco Borderless Network. There are 3 campuses, large, medium and small, connected via WAN/the Internet. The large campus has a main campus and three branch sites. It has a data center, services block and an internet edge. The internet edge is connected to a WAN and Internet cloud. The medium campus has a main campus and three branch sites. It has a data center and services block. It has a router on the edge of the network thats connected to a WAN and Internet cloud. The small campus has one building. It has a data center and services block. It has a router on the edge of the network thats connected to a WAN and Internet cloud. **Large Campus**Data CenterData CenterData CenterServices BlockServices BlockServices Block**Medium CampusSmall Campus**Internet EdgeWANInternet By combining this hardware infrastructure with policy-based software solutions, the Cisco Borderless Network provides two primary sets of services: network services, and user and endpoint services under the umbrella of an integrated management solution. It enables different network elements to work together, and allows users to access resources from any place, at any time, while providing optimization, scalability, and security. 11.1.4 Hierarchy in the Borderless Switched Network Creating a borderless switched network requires that sound network design principles are used to ensure maximum availability, flexibility, security, and manageability. The borderless switched network must deliver on current requirements and future required services and technologies. Borderless switched network design guidelines are built upon the following principles: - - - - These are not independent principles. Understanding how each principle fits in the context of the others is critical. Designing a borderless switched network in a hierarchical fashion creates a foundation that allows network designers to overlay security, mobility, and unified communication features. Two time-tested and proven hierarchical design frameworks for campus networks are the three-tier layer and the two-tier layer models. The three critical layers within these tiered designs are the access, distribution, and core layers. Each layer can be seen as a well-defined, structured module with specific roles and functions in the campus network. Introducing modularity into the campus hierarchical design further ensures that the campus network remains resilient and flexible enough to provide critical network services. Modularity also helps to allow for growth and changes that occur over time. Click each button for an example of each design. Three-Tier Model Two-Tier Model **Three-Tier Model** The figure shows an example of the three-tier model. At the top there are two clouds depicting the internet. There are redundant links connecting to two firewall routers. The routers have redundant links to two core layer multilayer switches. The switches have an EtherChannel between each other with four links. They also have redundant links to two distribution layer multilayer switches. The distribution layer switches have redundant links to three access layer switches. Two of the switches have links to access points. Both access points have connections to tablets. The access layer switches are also connected to IP phones and PCs. InternetInternetDistribution LayerAccess LayerCore Layer 11.1.5 Access, Distribution, and Core Layer Functions The access, distribution, and core layers perform specific functions in a hierarchical network design. Click each button for a description of the functions of each layer. Access Layer Distribution Layer Core Layer **Access Layer** The access layer represents the network edge, where traffic enters or exits the campus network. Traditionally, the primary function of an access layer switch is to provide network access to the user. Access layer switches connect to distribution layer switches, which implement network foundation technologies such as routing, quality of service, and security. To meet network application and end-user demand, the next-generation switching platforms now provide more converged, integrated, and intelligent services to various types of endpoints at the network edge. Building intelligence into access layer switches allows applications to operate on the network more efficiently and securely. 11.1.6 Three-Tier and Two-Tier Examples Click each button for an example and explanation of a three-tier and two-tier design. Three-Tier Example Two-Tier Example **Three-Tier Example** The figure shows a three-tier campus network design for organizations where the access, distribution, and core are each separate layers. To build a simplified, scalable, cost-effective, and efficient physical cable layout design, the recommendation is to build an extended-star physical network topology from a centralized building location to all other buildings on the same campus. The figure shows an example of the three-tier campus network design. There are six buildings named A through F. Building A is labeled Management, Building B is Marketing and Sales, Building C is Engineering, Building D is Research and Development, Building E is Information Technology and Building F is the Data center. Buildings B through F are connected to building A in a hub and spoke topology. Building A is at the Core layer. Building B through F are all at the distribution and access layers. **Building B**\ Marketing and Sales**AccessBuilding A**\ Management**DistributionCoreBuilding C**\ Engineering**DistributionAccessBuilding D**\ Research and Development**Building F**\ Data Center**Building E**\ Information Technology 11.1.7 Role of Switched Networks The role of switched networks has evolved dramatically in the last two decades. It was not long ago that flat Layer 2 switched networks were the norm. Flat Layer 2 switched networks relied on the Ethernet and the widespread use of hub repeaters to propagate LAN traffic throughout an organization. As shown in the figure, networks have fundamentally changed to switched LANs in a hierarchical network. The figure illustrates the role of switched networks in a hierarchical network. At the core layer there are two routers and two multilayer switches. The routers are on the outside of the multilayer switches. Between the multilayer switches are redundant links. Both switches are connected to two distribution layer multilayer switches, totaling four distribution switches. The distribution switches are separated into two pairs. Each pair has a link between them as well as redundant links to three access layer switches, totaling six access layer switches. The access layer switches have links to IP phones, printers and PCs. R1R2D1S1S2S3S4S5S6PC1PC2PC3D2D3D4C1C2 CoreDistributionAccess A switched LAN allows additional flexibility, traffic management, quality of service, and security. It also affords support for wireless networking and connectivity, and support for other technologies such as IP telephone and mobility services. **Scalable Networks** ===================== 11.2.1 Design for Scalability ---------------------- You understand that your network is going to change. Its number of users will likely increase, they may be found anywhere, and they will be using a wide variety of devices. Your network must be able to change along with its users. Scalability is the term for a network that can grow without losing availability and reliability. To support a large, medium or small network, the network designer must develop a strategy to enable the network to be available and to scale effectively and easily. Included in a basic network design strategy are the following recommendations: - Use expandable, modular equipment, or clustered devices that can be easily upgraded to increase capabilities. Device modules can be added to the existing equipment to support new features and devices without requiring major equipment upgrades. Some devices can be integrated in a cluster to act as one device to simplify management and configuration. - Design a hierarchical network to include modules that can be added, upgraded, and modified, as necessary, without affecting the design of the other functional areas of the network. For example, creating a separate access layer that can be expanded without affecting the distribution and core layers of the campus network. - Create an IPv4 and IPv6 address strategy that is hierarchical. Careful address planning eliminates the need to re-address the network to support additional users and services. - Choose routers or multilayer switches to limit broadcasts and filter other undesirable traffic from the network. Use Layer 3 devices to filter and reduce traffic to the network core. Click each button for more information about advanced network design requirements Redundant Links Multiple Links Scalable Routing Protocol Wireless Connectivity **Redundant Links** Implement redundant links in the network between critical devices and between access layer and core layer devices. The figure illustrates redundant links between access and core layer devices. In the wire closet there are two switches and in the backbone there are four switches. The six switches have redundant links. The backbone switches also have redundant links to the server farm. The server farm consist of two switches and seven servers. S1S5S2S6S7S3S8S4 Wiring\ ClosetBackbone with\ Redundant LinksServer Farm 11.2.2 Plan for Redundancy ------------------- For many organizations, the availability of the network is essential to supporting business needs. Redundancy is an important part of network design. It can prevent disruption of network services by minimizing the possibility of a single point of failure. One method of implementing redundancy is by installing duplicate equipment and providing failover services for critical devices. The figure illustrates redundant links between important devices on a network. In the wire closet there are two switches and in the backbone there are four switches. The six switches have redundant links. The backbone switches also have redundant links to the server farm. The server farm consist of two switches and seven servers. S1S5S2S6S7S3S8S4 **Wiring ClosetBackbone with Redundant LinksServer Farm** Another method of implementing redundancy is redundant paths, as shown in the figure above. Redundant paths offer alternate physical paths for data to traverse the network. Redundant paths in a switched network support high availability. However, due to the operation of switches, redundant paths in a switched Ethernet network may cause logical Layer 2 loops. For this reason, Spanning Tree Protocol (STP) is required. STP eliminates Layer 2 loops when redundant links are used between switches. It does this by providing a mechanism for disabling redundant paths in a switched network until the path is necessary, such as when a failure occurs. STP is an open standard protocol, used in a switched environment to create a loop-free logical topology. Using Layer 3 in the backbone is another way to implement redundancy without the need for STP at Layer 2. Layer 3 also provides best path selection and faster convergence during failover. 11.2.3 Reduce Failure Domain Size -------------------------- A well-designed network not only controls traffic, but also limits the size of failure domains. A failure domain is the area of a network that is impacted when a critical device or network service experiences problems. The function of the device that initially fails determines the impact of a failure domain. For example, a malfunctioning switch on a network segment normally affects only the hosts on that segment. However, if the router that connects this segment to others fails, the impact is much greater. The use of redundant links and reliable enterprise-class equipment minimize the chance of disruption in a network. Smaller failure domains reduce the impact of a failure on company productivity. They also simplify the troubleshooting process, thereby, shortening the downtime for all users. Click each button to see the failure domain of each associated device. Edge Router AP1 S1 S2 S3 **Edge Router** The figure illustrates the failure domain of an edge router. A cloud depicting the Internet is connected to an edge router. The edge router has two branched links to two switches named S1 and S2. S1 has links to two PCs labeled H2 and H3, and a wireless access point labeled, AP1. AP1 has a wireless connection to a laptop, labeled H1. The other switch S2 has a link to a switch labeled S3 and a PC labeled H4. S3 has two links to two PCs labeled H5 and H6. The failure domain for the edge router is highlighted in a square that encompasses all of the devices connected to the edge router only excluding the link to the Internet. H3H2H1H6H5H4S2S3AP1S1 Internet **Limiting the Size of Failure Domains** Because a failure at the core layer of a network can have a potentially large impact, the network designer often concentrates on efforts to prevent failures. These efforts can greatly increase the cost of implementing the network. In the hierarchical design model, it is easiest and usually least expensive to control the size of a failure domain in the distribution layer. In the distribution layer, network errors can be contained to a smaller area; thus, affecting fewer users. When using Layer 3 devices at the distribution layer, every router functions as a gateway for a limited number of access layer users. **Switch Block Deployment** Routers, or multilayer switches, are usually deployed in pairs, with access layer switches evenly divided between them. This configuration is referred to as a building, or departmental, switch block. Each switch block acts independently of the others. As a result, the failure of a single device does not cause the network to go down. Even the failure of an entire switch block does not affect a significant number of end users. 11.2.4 Increase Bandwidth ------------------ In hierarchical network design, some links between access and distribution switches may need to process a greater amount of traffic than other links. As traffic from multiple links converges onto a single, outgoing link, it is possible for that link to become a bottleneck. Link aggregation, such as EtherChannel, allows an administrator to increase the amount of bandwidth between devices by creating one logical link made up of several physical links. The figure illustrates increasing bandwidth by using EtherChannel and aggregating multiple links between switches. The figure has two multilayer switches with two links each to a switch. The links are aggregated together using EtherChannel. EtherChannelEtherChannel EtherChannel uses the existing switch ports. Therefore, additional costs to upgrade the link to a faster and more expensive connection are not necessary. The EtherChannel is seen as one logical link using an EtherChannel interface. Most configuration tasks are done on the EtherChannel interface, instead of on each individual port, ensuring configuration consistency throughout the links. Finally, the EtherChannel configuration takes advantage of load balancing between links that are part of the same EtherChannel, and depending on the hardware platform, one or more load-balancing methods can be implemented. 11.2.5 Expand the Access Layer ----------------------- The network must be designed to be able to expand network access to individuals and devices, as needed. An increasingly important option for extending access layer connectivity is through wireless. Providing wireless connectivity offers many advantages, such as increased flexibility, reduced costs, and the ability to grow and adapt to changing network and business requirements. To communicate wirelessly, end devices require a wireless NIC that incorporates a radio transmitter/receiver and the required software driver to make it operational. Additionally, a wireless router or a wireless access point (AP) is required for users to connect, as shown in the figure. The figure illustrates a Cisco wireless access point connecting wireless devices to the network. A router, R1, has a link to a switch, S1. S1 has redundant links to another switch, S2. S2 has links to two PCs and to a Cisco wireless access point. The Cisco wireless access point is connected wirelessly to a cell phone, laptop and tablet. R1S1S2PC1PC2 **Cisco Wireless\ Access Point** There are many considerations when implementing a wireless network, such as the types of wireless devices to use, wireless coverage requirements, interference considerations, and security considerations. 11.2.6 Tune Routing Protocols ---------------------- Advanced routing protocols, such as Open Shortest Path First (OSPF), are used in large networks. OSPF is a link-state routing protocol. As shown in the figure, OSPF works well for larger hierarchical networks where fast convergence is important. OSPF routers establish and maintain neighbor adjacencies with other connected OSPF routers. OSPF routers synchronize their link-state database. When a network change occurs, link-state updates are sent, informing other OSPF routers of the change and establishing a new best path, if one is available. The figure illustrates the use of using routing protocols in large networks. The figure shows three OSPF areas: Area 1, Area 0 and Area 51. Area 1 has four routers with one labeled R1 at the edge. R1 is in both Area 1 and Area 0. Area 0 has two routers: R1 and R2. R2 is in both Area 0 and Area 51. Area 51 consists of four routers connected via serial links. R1R2 **Switch Hardware** =================== 11.3.1 Switch Platforms ---------------- One simple way to create hierarchical and scalable networks is to use the right equipment for the job. There is a variety of switch platforms, form factors, and other features that you should consider before choosing a switch. When designing a network, it is important to select the proper hardware to meet current network requirements, as well as to allow for network growth. Within an enterprise network, both switches and routers play a critical role in network communication. Click each button for more information about the categories of switches for enterprise networks. Campus LAN Switches Cloud-Managed Switches Data Center Switches Service Provider Switches Virtual Networking **Campus LAN Switches** To scale network performance in an enterprise LAN, there are core, distribution, access, and compact switches. These switch platforms vary from fanless switches with eight fixed ports to 13-blade switches supporting hundreds of ports. Campus LAN switch platforms include the Cisco 2960, 3560, 3650, 3850, 4500, 6500, and 6800 Series.  11.3.2 Switch Form Factors ------------------- When selecting switches, network administrators must determine the switch form factors. This includes fixed configuration, modular configuration, stackable, or non-stackable Click each button for more information about switch form factors. Fixed configuration switches Modular configuration switches Stackable configuration switches Thickness **Fixed configuration switches** Features and options on fixed configuration switches are limited to those that originally come with the switch. The figure displays four fixed configuration switches stacked on top of one another. 11.3.3 Port Density ------------ The port density of a switch refers to the number of ports available on a single switch. The figure shows the port density of three different switches. Fixed configuration switches support a variety of port density configurations. The Cisco Catalyst 3850 come in 12, 24, 48 port configurations, as shown in the figure. The 48-port switch has an option for additional ports for small form-factor pluggable (SFP) devices. ### **Cisco Catalyst 3850 Switches**  Modular switches can support very high port densities through the addition of multiple switchport line cards. The modular Catalyst 9400 switch shown in the next figure supports 384 switchport interfaces. The figure displays a modular Catalyst 9400 switch. ### **Catalyst 9400 Switch** Large networks that support many thousands of network devices require high density, modular switches to make the best use of space and power. Without using a high-density modular switch, the network would need many fixed configuration switches to accommodate the number of devices that need network access. This approach can consume many power outlets and a lot of closet space. The network designer must also consider the issue of uplink bottlenecks. A series of fixed configuration switches may consume many additional ports for bandwidth aggregation between switches, for the purpose of achieving target performance. With a single modular switch, bandwidth aggregation is less of an issue because the backplane of the chassis can provide the necessary bandwidth to accommodate the devices connected to the switchport line cards. 11.3.4 Forwarding Rates ---------------- Forwarding rates define the processing capabilities of a switch by rating how much data the switch can process per second. Switch product lines are classified by forwarding rates. Entry-level switches have lower forwarding rates than enterprise-level switches. Forwarding rates are important to consider when selecting a switch. If the switch forwarding rate is too low, it cannot accommodate full wire-speed communication across all of its switch ports. Wire speed is the data rate that each Ethernet port on the switch is capable of attaining. Data rates can be 100 Mbps, 1 Gbps, 10 Gbps, or 100 Gbps. For example, a typical 48-port gigabit switch operating at full wire speed generates 48 Gbps of traffic. If the switch only supports a forwarding rate of 32 Gbps, it cannot run at full wire speed across all ports simultaneously. Fortunately, access layer switches typically do not need to operate at full wire speed, because they are physically limited by their uplinks to the distribution layer. This means that less expensive, lower performing switches can be used at the access layer, and more expensive, higher performing switches can be used at the distribution and core layers, where the forwarding rate has a greater impact on network performance. 11.3.5 Power over Ethernet ------------------- Power over Ethernet (PoE) allows the switch to deliver power to a device over the existing Ethernet cabling. This feature can be used by IP phones and some wireless access points, allowing them to be installed anywhere that there is an Ethernet cable. A network administrator should ensure that the PoE features are actually required for a given installation, because switches that support PoE are expensive. Click each button to view PoE ports on different devices. Switch IP Phone WAP Cisco Catalyst 2960-C **Switch** PoE ports look the same as any other switch port. Check the model of the switch to determine if the port supports PoE. The figure points to a PoE port on a Cisco 520 Wireless LAN Controller.  11.3.6 Multilayer Switching -------------------- Multilayer switches are typically deployed in the core and distribution layers of an organization\'s switched network. Multilayer switches are characterized by their ability to build a routing table, support a few routing protocols, and forward IP packets at a rate close to that of Layer 2 forwarding. Multilayer switches often support specialized hardware, such as application-specific integrated circuits (ASICs). ASICs along with dedicated software data structures can streamline the forwarding of IP packets independent of the CPU. There is a trend in networking toward a pure Layer 3 switched environment. When switches were first used in networks, none of them supported routing. Now, almost all switches support routing. It is likely that soon all switches will incorporate a route processor because the cost of doing so is decreasing relative to other constraints. The figure shows a Catalyst 2960. Catalyst 2960 switches illustrate the migration to a pure Layer 3 environment. With IOS versions prior to 15.x, these switches supported only one active switched virtual interface (SVI). With IOS 15.x, these switches now support multiple active SVIs. This means that the switch can be remotely accessed via multiple IP addresses on distinct networks. The figure displays five Cisco Catalyst 2960 switches stacked on top of each other. 11.3.7 Business Considerations for Switch Selection -------------------------------------------- The following table highlights other common business considerations when selecting switch equipment. ConsiderationDescriptionCostThe cost of a switch will depend on the number and speed of the interfaces, supported features, and expansion capability.Port densityNetwork switches must support the appropriate number of devices on the network.PowerIt is now common to power access points, IP phones, and compact switches user Power over Ethernet (PoE). In addition to PoE considerations, some chassis-based switches support redundant power supplies.ReliabilityThe switch should provide continuous access to the network.Port speedThe speed of the network connection is of primary concern to end users.Frame buffersThe ability of the switch to store frames is important in a network where they may be congested ports to servers or other areas of the network.ScalabilityThe number of users on a network typically grows over time: therefore, the switch should provide the opportunity for growth. -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- **Consideration** **Description** Cost The cost of a switch will depend on the number and speed of the interfaces, supported features, and expansion capability. Port density Network switches must support the appropriate number of devices on the network. Power It is now common to power access points, IP phones, and compact switches user Power over Ethernet (PoE). In addition to PoE considerations, some chassis-based switches support redundant power supplies. Reliability The switch should provide continuous access to the network. Port speed The speed of the network connection is of primary concern to end users. Frame buffers The ability of the switch to store frames is important in a network where there may be congested ports to servers or other areas of the network. Scalability The number of users on a network typically grows over time; therefore, the switch should provide the opportunity for growth. **Router Hardware** =================== 11.4.1 Router Requirements ------------------- Switches are not the only component of a network that come with a variety of features. Your choice of router is another very important decision. Routers play a critical role in networking by connecting homes and businesses to the internet, interconnecting multiple sites within an enterprise network, providing redundant paths, and connecting ISPs on the internet. Routers can also act as a translator between different media types and protocols. For example, a router can accept packets from an Ethernet network and re-encapsulate them for transport over a serial network. Routers use the network portion (prefix) of the destination IP address to route packets to the proper destination. They select an alternate path if a link goes down. All hosts on a local network specify the IP address of the local router interface in their IP configuration. This router interface is the default gateway. The ability to route efficiently and recover from network link failures is critical to delivering packets to their destination. Routers also serve other beneficial functions as follows: - They provide broadcast containment by limiting broadcasts to the local network. - They interconnect geographically separated locations. - They group users logically by application or department within a company, based on common needs or requiring access to the same resources. - They provide enhanced security by filtering unwanted traffic through access control lists. 11.4.2 Cisco Routers ------------- As the network grows, it is important to select the proper routers to meet its requirements. There are different categories of Cisco routers. Click each button for more information about the categories of routers. Branch Routers Network Edge Routers Service Provider Routers Industrial **Branch Routers** Branch routers, shown in the figure, optimize branch services on a single platform while delivering an optimal application experience across branch and WAN infrastructures. Maximizing service availability at the branch requires networks designed for 24x7x365 uptime. Highly available branch networks must ensure fast recovery from typical faults, while minimizing or eliminating the impact on service, and provide simple network configuration and management. Shown are the Cisco Integrated Services Router (ISR) 4000 Series Routers.  11.4.3 Router Form Factors ------------------- Like switches, routers also come in many form factors. Network administrators in an enterprise environment should be able to support a variety of routers, from a small desktop router to a rack-mounted or blade model. Click each button for more information on various Cisco router platforms. Cisco 900 Series ASR 9000 and 1000 Series 5500 Series Cisco 800 **Cisco 900 Series** This is a small branch office router. It combines WAN, switching, security, and advanced connectivity options in a compact, fanless platform for small and medium-sized businesses. The figure displays a Cisco 900 series router. Routers can also be categorized as fixed configuration or modular. With the fixed configuration, the desired router interfaces are built-in. Modular routers come with multiple slots that allow a network administrator to change the interfaces on the router. Routers come with a variety of different interfaces, such as Fast Ethernet, Gigabit Ethernet, Serial, and Fiber-Optic. A comprehensive list of Cisco routers can be found by searching Cisco\'s website [www.cisco.com](http://www.cisco.com/).