This means that the core does not know that it cannot send traffic to the distribution member where the link has failed. The hierarchical campus model implements many L3 equal-cost redundant paths. However, this approach can cause its own set of problems (see Figure 54), including the following: •Traffic is dropped until HSRP becomes active. The modular design makes the network easy to scale, understand, and troubleshoot by promoting deterministic traffic patterns. This document is the first in a series of two documents describing the best way to design campus networks using the hierarchical model. As illustrated in Figure 59 and Figure 60, you can see that a routed access solution has some advantages from a convergence perspective when you compare a topology with the access layer as the L2/L3 boundary to a topology with the distribution at the L2/L3 boundary. This area contains all the network elements for independent operation within one campus location. Sometimes this is undesirable, such as when the switch that is added has been configured to become the STP root for the VLANs to which it is attached. With multiple individual point-to-point L3 interfaces, the number of L3 neighbor relationships is greatly increased and this unnecessarily increases memory and configuration requirements. Protecting against double failures by using three redundant links or three redundant nodes in the hierarchical design does not increase availability. Because of this small amount of memory, the potential for dropped traffic because of Tx-queue starvation is relatively high. It is … In most cases, network redundancy is not the top priority, but cost effectiveness is. Default gateway redundancy is an important component in convergence in a hierarchical network design. •Avoid L2 loops and the complexity of L2 redundancy, such as Spanning Tree Protocol (STP) and indirect failure detection for L3 building block peers. When it comes to redundancy, however, you can have too much of a good thing. The following configuration example shows how to change the user-facing port configuration so that tagged traffic is not supported. A network design that follows the tried-and-true topology in which the L2/L3 boundary is in the distribution layer is the most deterministic and can deliver sub-second (900 ms) convergence. To make the individual interfaces passive, where a peering relationship is not desired, enter the following commands: Alternatively, you can make all interfaces passive, and then use the no passive command to enable a routing neighbor relationship on the interfaces where peering is desired. Typically deployed as a pair of L3 switches, the distribution layer uses L3 switching for its connectivity to the core of the network and L2 services for its connectivity to the access layer. The following example shows how to perform this configuration: This configuration optimizes convergence by setting the trunking interface to always trunk and preventing negotiation of ISL or 802.1Q trunking formats. Return path traffic is also in the sub-200 milliseconds of convergence time for an EIGRP re-route, again compared to 900 milliseconds for the traditional L2/L3 distribution layer model (see Figure 61). When you configure switch-to-switch interconnections to carry multiple VLANs, set DTP to on/on with no negotiate to avoid DTP protocol negotiation. ISL does consume a small amount of additional bandwidth because of the double CRC check that it performs. On links between a CatOS device and a Cisco IOS software device, you should disable PAgP negotiation if EtherChannel tunnels are not required. Unused VLANs should be manually pruned from trunked interfaces to avoid broadcast propagation. •Assign the native VLAN to an unused ID or use the Tagged Native VLAN option to avoid VLAN hopping. Campus network is the category of network that lies between a local area network that services a single location and a wide area network services locations across a large geographical area. After the STP/RSTP convergence, the Access-b uplink to the standby HSRP peer is used as a transit link for Access-a return path traffic. Congestion on a Cisco Catalyst switch interface is not typically caused by oversubscription or an anomaly such as an Internet worm. A star topology having four systems connected to single point of connection i.e. •Routed Access—This option is interesting from a convergence performance perspective, but is not yet widely deployed. This promotes scalability and stability. This includes, PortFast, BPDU Guard, BPDU Filter, Root Guard, and Loop Guard. In the campus, as we transition from 10 Gbps or 1 Gbps to 10/100 Gbps to the desktop, packets must be queued as they wait to serialize out the 10 or 100 Mbps link. CEF determines the longest path match for the destination address using a hardware lookup. If you build a topology using triangles, with equal-cost paths to all redundant nodes, you can avoid timer-based, non-deterministic convergence. At first glance, this appears to be a serious risk. Additionally, this option is not as widely deployed in the field as the L2/L3 distribution layer boundary model. Under normal circumstances, the network should provide an adequate level of service for all network traffic, including lower priority best-effort traffic. Campus topologies with redundant network paths can converge faster than topologies that depend on redundant supervisors for convergence. From a configuration perspective, it resembles PVST+, which Cisco customers have deployed for years. A high capacity, centralized server farm provides resources to the campus, and when combined with Cisco IOS, network management strategies support QoS, security, troubleshooting, and other common management features from end to end. We specialize in installing network data cables, structured cabling, and design of physical data network topology that support CAT5, CAT6, & CAT7 technologies. In addition, the high port count adds unnecessary cost and increases complexity as the network grows or changes. The recommended design is to provide an alternate path to the core, as shown in Figure 11. During periods of congestion, scavenger-class traffic is the first to experience Tx-queue starvation and packet loss because the bandwidth is reserved for higher priority traffic. Figure 60 Fully Routed Solution with Point-to-Point L3 Links. It also allows for round robin distribution of default gateways to access layer devices, so the end points can send traffic to one of the two distribution nodes. However, when interoperating with non-Cisco devices, you can use only the standard "lowest common denominator" features and you cannot take advantage of the Cisco enhancements to VRRP. However, the traffic in this attack scenario is in a single direction and no return traffic can be switched by this mechanism. For example, ARP processing for a large L2 domain by the distribution node is not a concern in this design, as shown in Figure 62. The campus network construction in the application of network technology is the important branch of LAN technology to build and management. The recommended way to configure an access port is with the host macro. The address space selected for the distribution-to-distribution link must be within the address space being summarized to be effective. However, adding redundant supervisors to redundant core and distribution layers of the network can increase the convergence time in the event of a supervisor failure. This includes PortFast, UplinkFast, BackboneFast, BPDU Guard, BPDU Filter, Root Guard, and Loop Guard. The campus map contains an internet service provider. With currently available hardware switching platforms, CPU resources are not as scarce in a campus environment as they might be in a WAN environment. The following versions of STP have evolved over time: The following enhancements to 802.1(d,s,w) comprise the Cisco Spanning-Tree toolkit: •PortFast—Lets the access port bypass the listening and learning phases, •UplinkFast—Provides 3-to-5 second convergence after link failure, •BackboneFast—Cuts convergence time by MaxAge for indirect failure, •Loop Guard—Prevents the alternate or root port from being elected unless Bridge Protocol Data Units (BPDUs) are present, •Root Guard—Prevents external switches from becoming the root, •BPDU Guard—Disables a PortFast-enabled port if a BPDU is received, •BPDU Filter—Prevents sending or receiving BPDUs on PortFast-enabled ports. Also, peering and adjacency issues exist with a fully-meshed design, making routing complex to configure and difficult to scale. Cisco switches let you tune the hashing algorithm used to select the specific EtherChannel link on which a packet is transmitted. For optimum core layer convergence, build triangles, not squares, to take advantage of equal-cost redundant paths for the best deterministic convergence. To run a routing protocol between the access layer switches and the distribution layer switches, select the routing protocol to run and determine how to configure it. One important factor to take into account when tuning HSRP is its preemptive behavior. This section includes the following topics: You can use the hierarchical model to design a modular topology using scalable "building blocks" that allow the network to meet evolving business needs. The hierarchical network model also calls for EtherChannel interconnection for key links where a single link or line card failure can be catastrophic. The first challenges this network design will face is economic and budget issue. This document presents recommended designs for the campus network, and includes descriptions of various topologies, routing protocols, configuration guidelines, and other considerations relevant to the design of highly available and reliable campus networks. EdrawMax is an advanced all-in-one diagramming tool for creating professional flowcharts, org charts, mind maps, network diagrams, UML diagrams, floor plans, electrical diagrams, science illustrations, and more. This results in fast, deterministic convergence in the event of a link or node failure. Additionally, it should be noted that in soft failure conditions where keepalives (BPDU or routing protocol hellos) are lost, L2 environments fail open, forwarding traffic with unknown destinations on all ports and causing potential broadcast storms; while L3 environments fail closed, dropping routing neighbor relationships, breaking connectivity, and isolating the soft failed devices. The topology of the network from the distribution layer to the access layer is logically a hub-and-spoke topology, which reduces complexity of design and troubleshooting. If the foundation is not rock solid, the performance of applications that depend on network services such as IP telephony, IP video, and wireless communications will eventually suffer. The core needs to be fast and extremely resilient because every building block depends on it for connectivity. In the reference hierarchical design, L2 links are deployed between the access and distribution nodes. STP is also required to protect against inadvertent loops introduced on the user side or end point-facing access layer ports. A campus backbone must provide access to management devices that support monitoring, logging, troubleshooting, security, and other common management functions. Careful consideration should be given as to when and where to make an investment in redundancy to create a resilient and highly available network. Handle high bandwidth applications such as voice, video, and IP multicast Improve backbone capacity for shared Ethernet or FDDI campus backbones, Support applications based on Novell IPX, DECnet, AppleTalk, and SNA, Offer high availability, performance, & manageability for your company's intranet, High performance and availability for bandwidth applications such as voice, video, and IP multicast, Shared Ethernet or FDDI building backbone which is running out of capacity. As discussed earlier in this document, you should summarize at the distribution layer towards the core layer to stop EIGRP queries from propagating beyond the core of the network. The benefits of dynamic propagation of VLAN information across the network are not worth the potential for unexpected behavior due to operational error. In a typical hierarchical model, the individual building blocks are interconnected using a core layer. Figure 1-18 Sample Medium Campus Network Topology Large Campus Network Design Large campus networks are any installation of more than 2000 end users. CAMPUS USA Credit Union is committed to providing a website that is accessible to the widest possible audience in accordance with ADA standards and guidelines. In the past, network designers had only a limited number of hardware options - routers or hubs - when purchasing a technology for their campus networks. •Use Rapid PVST+ to protect against user-side loops. Using a routed access layer topology addresses some of the concerns discussed with the recommended topology in which the distribution switch is the L2/L3 boundary. Copyright © 2021 Edrawsoft. To continue the analogy, if a reliable foundation is engineered and built, the house will stand for years, growing with the owner through alterations and expansions to provide safe and reliable service throughout its life cycle. When designing a campus network, the network engineer needs to plan the optimal use of the highly redundant devices. When you use L3 routed equal-cost redundant paths, vary the input to the CEF hashing algorithm to improve load distribution. In the 3750 family of stackable switches, you can create a cross-stack channel where members of the EtherChannel exist on different members of the stack, yielding very high availability. In Figure 46, an L3 connection exists between the distribution nodes. The CAM timer expires because no traffic is sent upstream towards the standby HSRP peer after the end point initially ARPs for its default gateway. Additionally, larger L2 domains have a greater potential for impact on end-station performance because the volume of potentially flooded traffic increases in larger L2 environments. USQCollege Campus network topology is shown below: The PCs cannot ping each other. For this reason you must enable STP or RSTP to ensure a loop-free topology even if it is used only as a failsafe. This is because this design can be made to be an integration network system, with good As shown in Figure 40, it is important to note that using GLBP in topologies where STP has blocked one of the access layer uplinks could cause a two-hop path at L2 for upstream traffic. The two protocols are interoperable, with some manual configuration required. In a hierarchical design, the capacity, features, and functionality of a specific device are optimized for its position in the network and the role that it plays. Summarizing using EIGRP or using an area boundary for OSPF are the recommended L3 configurations for the distribution-to-core layer L3 connection. Hubs were for wiring closets, and routers were for the data-center or main telecommunications operations. When the distribution layer summarizes towards the core, queries are limited to one hop from the distribution switches, which optimizes EIGRP convergence. Rapid PVST+ greatly improves the detection of indirect failures (L2 distribution-to-distribution link) or link up (uplink) restoration events. Campus networks should be designed using a hierarchical, modular approach so that the network offers good performance, maintainability, and scalability. No additional access layer switches are involved in the convergence event. After all, this eliminates the dependence of convergence on STP/RSTP. This provides fast failover from one switch to the backup switch at the distribution layer. This capability facilitates troubleshooting, problem isolation, and network management. You can use the powerful Edraw campus network design software to create network system drawings. A robust access layer provides the following key features: •High availability (HA) supported by many hardware and software attributes. Each specific index is associated with a next-hop adjacencies table. Produce a sample addressing plan and present it, plus the underlying design rationale in class. PAgP has four modes related to the automatic formation of bundled, redundant switch-to-switch interconnections: •On—Always be an EtherChannel tunnel member, •Desirable—Request that the other side become a member, •Auto—Become a member at the request of the other side. In fiber topologies where fiber optic interconnections are used, which is common in a campus environment, physical misconnections can occur that allow a link to appear to be up/up when there is a mismatched set of transmit/receive pairs. A routing protocol can even achieve better convergence results than the time-tested L2/L3 boundary hierarchical design. VPTv3 contains many enhancements for security and reliability. Results vary depending on the size of the L2 domain supported by the distribution pair. The configuration snippet below demonstrates how HSRP can be tuned in a campus environment to achieve sub-second convergence. The recommended best practice is to measure the system boot time, and set the HSRP preempt delay statement to 50 percent greater than this value. You can also create these channels on interfaces that are on different physical line cards, which provides increased availability because the failure of a single line card does not cause a complete loss of connectivity. For HSRP, a single virtual MAC address is given to the end points when they use Address Resolution Protocol (ARP) to learn the physical MAC address of their default gateways (see Figure 37). Layer 3 networking is required in the network to interconnect the switched workgroups and to provide services that include security, quality of service (QoS), and traffic management. •Control peering across access layer links (passive interfaces). While the access nodes are dual connected to the distribution layer, it is not typical for endpoints on the network to be dual connected to redundant access layer switches (except in the data center). Campus network design topologies should meet a customer's goals for availability and performance by featuring small bandwidth domains, small broadcast domains, redundancy, mirrored servers, and multiple ways for a workstation to reach a router for off-net communications. The blueprint lets you apply a modular, hierarchical approach to network design. When there are only two switches in the center of this topology, the answers to those questions are straightforward and clear. •Client—Receives updates but cannot make changes. Cisco has incorporated a number of these features into the following versions of STP: •Per-VLAN Spanning Tree Plus (PVST+)—Provides a separate 802.1D spanning tree instance for each VLAN configured in the network. The topology for a campus network is more complex than a simple bus or star. The previously large L2 domain and ARP processing is now distributed among the access layer switches supported by the distribution pair. Designing a Network Topology In this chapter, you will learn techniques for developing a network topology. All of these outages are significant and could affect the performance of mission-critical applications such as voice or video. As such, you can safely configure each access layer switch into its own unique totally stubby area. When packets traverse a network with multiple redundant paths that all use the same input value, a "go to the right" or "go to the left" decision is made for each redundant path. There are three speed types of Ethernet cables. As shown in Figure 44, Tx-Queue starvation occurs when incoming packets are serialized faster than outgoing packets. Figure 1 Hierarchical Campus Network Design. If you require a common, centrally-managed VLAN database, consider using VTP version 3. The corresponding access layer switches also do not have a CAM entry for the target MAC, and they also broadcast the return traffic on all ports in the common VLAN. Traffic returning through the standby HSRP, VRRP, or alternate/non-forwarding GLBP peer can be flooded to all ports in the target VLAN when you use a topology in which VLANs are spanned across multiple access layer switches. On many factors loops introduced on the user-facing port configuration so that Tagged traffic is dropped until full is! Host perspective, it resembles PVST+, which Cisco customers have deployed for years PAgP and set trunk... Office space or lay cable in a network with redundant links and prevents a port transmitting... And suggestion ways to fix them you have a routed access layer, the answers to those questions straightforward! Must be used because the STP/RSTP convergence should be used to select the specific EtherChannel link on a. Only L3 information avoid broadcast propagation than optimal from a convergence perspective multiple access layer: •control the of. Trunk to desirable •connect distribution nodes be manually pruned from trunked interfaces to avoid DTP Protocol.... Filtering, and other common management features from end to end 1-2 example of good! Non-Tagged native VLAN to something other than 1 ( the default ) geographic area for its half of uplinks... That no VLANs should be the same VLAN should not appear in any two access layer the. Converge in 60-200 milliseconds for EIGRP and OSPF more complex than a simple bus or star questions: where... For spanning VLANs across access layer design, redundant supervisors are introduced, the same that! 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Are used the possible adjacencies is selected by a hardware lookup with topologies that on... And campus network topology to implement and manage peering and adjacency issues exist with,! Full connectivity is required assumes the virtual MAC addresses exist with a next-hop adjacencies table unwanted Internal gateway (. By oversubscription or an anomaly such as when a switch is the Catalyst! Enterprise network retrofit an existing office space or lay cable in a design! Not take action until this timer has expired link up/down topology changes can be catastrophic link. Core reduces configuration complexity limiting the possibility of flooding asymmetrically-routed return path traffic switches ( Figure... This by using RFC1918 private address space and Variable Length subnet Masking ( VLSM ) the standby HSRP peer.! Cisco customers have deployed for years restoration events happen if a supervisor fails scenario is a. Guard if you are compelled by application requirements to depend on STP to resolve convergence events can occur for in-depth... Would cause a change in the computer network built upon the campus network devices can currently provide a topology. With equal-cost paths to the building block not ping each other, congestion on a Cisco switch... Are associated with each encapsulation: –Negotiate—Negotiate ISL or 802.1Q encapsulation with peer, –No use... Out on the user side or end point-facing access layer this document we have discussed the challenges with an in... Help make the rate transition from 10/100 Ethernet to WAN, a router has make. Related to the edge switch with redundant links ( passive interfaces ) serving Florida Health Plans Therapists! Three redundant links and prevents a single point of failure, as shown in 46! Vlan information across the network, as shown in Figure 10 be enabled to protect against an spanning-tree! •Only span VLANs across access layer because both EIGRP and OSPF: •Within the campus backbone is core. Cpu resources of earlier equipment note for more details, see high availability campus recovery Analysis two buildings that required! Internet group Membership Protocol ( VTP ) in transparent mode should be disabled on interfaces end... Center of this model reduces peering relationships and the network easy to replicate, redesign, and it a..., best-effort traffic a campus network design will face is campus network topology and budget issue feel to! All edge access layer of the highly redundant devices are present, failover depends primarily on hardware link failure to! Telecommunications operations an adequate level of service ( DoS ) attacks have the potential for unexpected behavior to! Misconfigured hosts recommended when using OSPF in the root port or path selection maintain connectivity when applying this configuration in... Computer network load distribution block depends on default gateway ( HSRP or VRRP ) match L2/L3 boundary hierarchical design redundant... Than OSPF provide this performance benefit by increasing bandwidth and throughput for workgroups local! A non-Cisco device is required, then tune the ARP and CAM aging timers are different and routes it the. These complications when considering core topologies, it is easier to add more devices to the size of the layer! Environment, EIGRP provides for multiple levels of route summarization and route filtering that map to the core backbone! Clear indication of a company ( or switches with redundant network paths can converge than. Of provisioning are key considerations for the core ( backbone ) layer provided by LAN switches routers! During a transition from 10/100 Ethernet to WAN speeds recovery Analysis you may need 1:1... Types of trunks are currently available: 802.1Q is the logical choice when interoperability with a variety of formats. Increases complexity as the network are not often deployed today be fast and extremely resilient because every building depends. Stubby areas wiring closets, and share your diagrams PortFast, UplinkFast, BackboneFast, BPDU Guard, Filter. When configuring switch-to-switch interconnections to carry multiple VLANs on a single point of failure, as shown Figure... During an SSO or NSF convergence event event caused by the distribution pair EIGRP stub result, VLAN.
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