The hierarchies tied together at the campus backbone. The basic element in a campus network design is the switch block. http://www.cisco.com/en/US/docs/solutions/Enterprise/Data_Center/VMDC/2.6/vmdcservicesaag.html, http://www.cisco.com/en/US/docs/solutions/Enterprise/Data_Center/VMDC/2.6/vmdctechwp.html. 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. I have VSS setup and its working fine. If you want the best convergence available and you can ensure that no VLAN will need to span multiple access layer switches, then using a routed access layer topology is a viable design alternative. HSRP. Therefore, make sure you maintain connectivity when applying this configuration. Does one exist just for 2.6? From a connectivity perspective, some network designers recommend dual distribution nodes that are individually connected to a single core node member. Figure 39 GLBP, HSRP, and VRRP Test Results. Unified Communications services (Cisco Unified Communications Manager, gateways, MTP, and the like). Layer 3 core designs are superior to Layer 2 and other alternatives because they provide: –Faster convergence around a link or node failure. When the CAM entry has aged out and is removed, the standby HSRP peer must forward the return path traffic to all ports in the common VLAN. This allows for the failure or removal of one of the distribution nodes without affecting end point connectivity to the default gateway. Figure 12 Recommended Topology (Links Between Two Distribution Nodes). •Hard set the trunk mode to on and the encapsulation negotiate to off for optimal convergence. When applied to a building, the Cisco Campus … PVST+ with UplinkFast reduces this to 3-5 seconds, and Rapid PVST+ further reduces the outage to one second. In a test environment using a typical IP addressing scheme of one subnet per VLAN and two VLANs per access switch using the RFC1918 private address space, the default L3 algorithm provided about one-third to two-thirds utilization. It is possible to build a topology that does not rely on equal-cost redundant paths to compensate for limited physical fiber connectivity or to reduce cost. Therefore, when tuning for optimum performance, disable PAgP and set the channel members to on/on. As it shown in the figure above, a typical large Cisco modular Campus network consists of the fowling building blocks: It provides a very limited set of services and is designed to be highly available and operate in an always-on mode. You can use BPDU Guard to stop all bridge devices, such as switches, from being added to your network. Cisco switches let you tune the hashing algorithm used to select the specific EtherChannel link on which a packet is transmitted. Use the CatOS set port host or the Cisco IOS software switchport host commands to disable trunking and EtherChannel, and to enable STP PortFast. Rapid PVST+ provides the rapid convergence of 802.1w while avoiding the complexity of 802.1s. The access layer is the first point of entry into the network for edge devices, end stations, and IP phones (see Figure 5). Additionally, if you use a modular chassis switch, such as the Cisco Catalyst 4500 or Catalyst 6500 family of switches, these design considerations are not required. Each specific index is associated with a next-hop adjacencies table. For the same events, where 60-200 milliseconds of packet loss occurred without redundant supervisors when dual supervisor nodes were used in the core or distribution, 1.8 seconds of loss was measured. Only use L2 looped topologies if it cannot be avoided. The content of this book focuses on the prepare phase, plan phase, and design phases of the PPDIOO process as applied to building an enterprise campus network. Many redundant paths are provided in the recommended network topology. It is possible for HSRP neighbor relationships to form and preemption to occur before the primary switch has L3 connectivity to the core. When you use EtherChannel interconnections, use L3 and L4 information to achieve optimum utilization. • Traffic is dropped until the link transitions to forwarding state, taking as long as 50 seconds. In general, there is no technical reason to use one or the other. Some of the factors that can be considered for slecting an IGP for a campus LAN: For more details refer to the following link, cisco Borderless campus design, routing resign principles: http://www.cisco.com/en/US/docs/solutions/Enterprise/Campus/Borderless_Campus_Network_1.0/BN_Campus_Technologies.html#wp1053601. Current hardware accelerated systems have the potential to deliver complex services at wire speed. When it comes to redundancy, however, you can have too much of a good thing. However, the traffic in this attack scenario is in a single direction and no return traffic can be switched by this mechanism. Figure 55 Convergence Events with an Uplink Failure. The core needs to be fast and extremely resilient because every building block depends on it for connectivity. The switches in the access layer are connected to two separate distribution layer switches for redundancy. Designing a campus network may not appear as interesting or exciting as designing an IP telephony network, an IP video network, or even designing a wireless network. This means that the core does not know that it cannot send traffic to the distribution member where the link has failed. Network changes and upgrades can be performed in a controlled and staged manner, allowing greater flexibility in the maintenance and operation of the campus network. Advances in routing protocols and campus hardware have made it viable to deploy a routing protocol in the access layer switches and use an L3 point-to-point routed link between the access and distribution layer switches. GLPB is configured and functions like HSRP. 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. This document includes the following sections: This document is intended for customers and enterprise systems engineers who are building or intend to build an enterprise campus network and require design best practice recommendations and configuration examples. Figure 41 illustrates the STP topology after changing STP port cost on the secondary root switches interface facing the primary root switch (the distribution to distribution link) allowing traffic to flow up both uplinks from the access layer switches to both GLBP Virtual MAC addresses. •L3 in the access is an emerging and intriguing option. From an STP perspective, both access layer uplinks are forwarding, so the only convergence dependencies are the default gateway and return path route selection across the distribution-to-distribution link (see Figure 58). This helps the network designer and architect to optimize and select the right network hardware, software and features to perform specific roles for that network layer. As a result, no additional end stations are affected by the flooded traffic (see Figure 52). However, it is not possible to achieve the same deterministic convergence in the event of a link or node failure, and for this reason the design will not be optimized for high availability. Typical traffic flows in the campus cross multiple redundant paths as traffic flows from the access layer across the distribution and core and into the data center. To avoid this situation the Spanning Tree environment must be tuned so that the L2 link between the distribution switches is the blocking link while the uplinks from the access layer switches are in a forwarding state. The previously large L2 domain and ARP processing is now distributed among the access layer switches supported by the distribution pair. One important factor to take into account when tuning HSRP is its preemptive behavior. •Deploy QoS end-to-end; protect the good and punish the bad. Figure 32 Port Aggregation Protocol Operation. • Avoid asymmetric routing and unicast flooding; do not span VLANs across the access layer. When the packet reaches the target switch, the inner or second tag is then processed and the potentially malicious packet is switched to the target VLAN (see Figure 26). •Use redundant point-to-point L3 interconnections in the core (triangles, not squares) wherever possible, because this design yields the fastest and most deterministic convergence results. In this topology, no VLANs span access layer switches and the distribution layer interconnection is an L3 point-to-point link. This L2 looped topology is configuration and management intensive. Get validated design guidance on our open, software-driven approach to deploy a digital-ready network. When the link from Access-a to the STP root and the HSRP primary switch fails, traffic is lost until the standby HSRP peer takes over as the default gateway. As with Trunking/DTP, the long-standing practice for EtherChannel/PAgP has been to set one side of the interconnection (typically the access switch) to auto and the other side (typically the distribution switch) to desirable. In a typical hierarchical model, the individual building blocks are interconnected using a core layer. When redundant paths are present, failover depends primarily on hardware link failure detection instead of timer-based software failure detection. The following are additional considerations when comparing EIGRP and OSPF: •Within the campus environment, EIGRP provides for faster convergence and greater flexibility. When redundant supervisors are introduced, the links are not dropped during an SSO or NSF convergence event if a supervisor fails. If StackWise technology is utilized, you can follow the best practice recommendation by using an L3 connection between the distribution switches without having to use a loop-back cable or perform extra configuration. •When something goes wrong, how do you find the source of the problem? A routing protocol like EIGRP, when properly tuned, can achieve better convergence results than designs that rely on STP to resolve convergence events. In the topology shown in Figure 57, the following convergence times can be observed: •With PVST+ (with UplinkFast)—Up to 5 seconds, •With Rapid PVST+ (address by the protocol)—1 second. Additionally, this option is not as widely deployed in the field as the L2/L3 distribution layer boundary model. For more details please refer to the following link: http://www.cisco.com/en/US/docs/solutions/Enterprise/Campus/campover.html#wp708886. The following are some of the other key design issues to keep in mind: •Design the core layer as a high-speed, Layer 3 (L3) switching environment utilizing only hardware-accelerated services. GLBP provides HSRP-like redundancy and failure protection. The design principles and implementation best practices described in this document are tried-and-true lessons learned over time. However, this approach can cause its own set of problems (see Figure 54), including the following: •Traffic is dropped until HSRP becomes active. •Consider EIGRP/Routing in the access layer. Additionally, this attack cannot work unless the attacker knows the native VLAN ID. Enable UDLD aggressive mode in all environments where fiber optic interconnections are used. I currently have a 6506-E with a single SUP 720 as one of my distributions for access switches and last night I had an issue with a TM_DATA_PARITY_ERROR and sent this SUP into ROMMON mode. In general, when you avoid STP/RSTP, convergence can be predictable, bounded, and reliably tuned. The Access-b uplink to the backup HSRP peer to Access-b is now a transit link for Access-a traffic, and the Access-b uplink to the primary HSRP peer must now carry traffic for both Access-b (its original intent) and for Access-a. The access layer is not used as a transit area in a campus environment. Modularity: By separating the various functions that exist on a network into modules, the network is easier to design. Support for network virtualisation e.g. ARP processing is rate limited in Cisco IOS software and in hardware to protect the CPU against DoS attacks that might overrun the CPU with an extraordinary number of ARP requests. 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. If your applications require spanning VLANs across access layer switches and using STP as an integral part of your convergence plan, take the following steps to make the best of this suboptimal situation: •Use Rapid PVST+ as the version of STP. When congestion does occur, QoS is required to protect important traffic such as mission-critical data applications, voice, and video. Layer 3 routing protocols are typically deployed in the core-to-core and core-to-distribution layers of the network, and can be used all the way to the access layer. If you use a topology where spanning-tree convergence is required, then Rapid PVST+ is the best version. •Avoid L2 loops and the complexity of L2 redundancy, such as Spanning Tree Protocol (STP) and indirect failure detection for L3 building block peers. A separate core provides the ability to scale the size of the campus network in a structured fashion that minimizes overall complexity when the size of the network grows and the number of interconnections required to tie the campus together grow. This design … Trunking protocols allow network node interconnections (uplinks) to carry multiple VLANS through a single physical link, as shown in Figure 22. Figure 46 L3 Connection Between Distribution Nodes. A campus network is an enterprise network … To achieve this, use the mls ip cef load-sharing full command on the distribution nodes. Additional requirements of these designs typically include: Design suggestions This Cisco solution provides manageable switched infrastructure for a campus intranet with over a thousand networked devices. Figure 57 Best Practice Topology for Spanning VLANs Across Access Layer Switches. Cisco Network Examples and Templates. Additionally, traffic engineering or link capacity planning for both outbound and return path traffic is difficult and complex, and you must plan to support the traffic for at least one additional access layer switch. Summarizing using EIGRP or using an area boundary for OSPF are the recommended L3 configurations for the distribution-to-core layer L3 connection. The Cisco Certified Design Associate (CCDA®) is an industry-recognized certification for network design engineers, technicians, and support engineers who demonstrate the skills required to … However, the implications of LSA propagation and SPF calculation on the network as a whole are unknown in a campus topology where non-stubby areas are used for the access layer. Failover and convergence work just like HSRP. This section describes the best way to build a topology that includes VLANs spanning access layer switches and that depend on STP/RSTP for convergence (see Figure 57). These areas allow network designers and engineers to associate specific network … Figure 7 Potential Single Points of Failure. Always perform QoS in hardware rather than software when a choice exists. In the distribution layer, change the default CEF load balancing behavior and use L3 and L4 information as input into the CEF hashing algorithm. An L3 link is required between the distribution nodes. The campus network covers the entire campus, and the network design follows the following five basic principles: Reliability and high performance networks must be reliable, including network-level … Internet worms and denial of service (DoS) attacks have the ability to flood links even in a high-speed campus environment. You can use the default source/destination IP information, or you can add an additional level of load balancing to the process by adding the L4 TCP/IP port information as an input to the algorithm. By using the EIGRP stub option, you optimize the ability of EIGRP to converge in the access layer and also optimize its behavior from a route processing perspective. What is a “campus” network anyway? Additionally, in a less than optimal design where VLANs span multiple access layer switches, the distribution nodes must be linked by an L2 connection. See the "Routing in the Access Layer" section for a in-depth discussion of routed access layer designs. Summarization is required to facilitate optimum EIGRP or OSPF convergence. With standard STP, this can take as long as 50 seconds. Additionally, the distribution-to-distribution link is an L3 routed link. The campus wired LAN enables communications between devices in a building or group of buildings, as well as interconnection to the WAN and Internet edge at the network … Figure 34 First Hop Default Gateway Redundancy. The distribution switches become ABRs with their core-facing interfaces in area 0 and the access layer interfaces in unique totally stubby areas for each access layer switch. Although this option allows for the safest deployment, there is a performance cost when a link or node is restored and channel negotiation occurs. This results in fast, deterministic convergence in the event of a link or node failure. You can reliably tune HSRP/GLBP timers to achieve 900 ms convergence for link/node failure in the L2/L3 boundary in the distribution hierarchical model. It will be essential to integrate these services into the campus smoothly—while providing for the appropriate degree of operational change management and fault isolation and continuing to maintain a flexible and scalable design. Two things can happen if a link or node in the middle of the chain or stack fails. This causes yet another convergence event when Access-a end points start forwarding traffic to the primary HSRP peer. •Prioritization of mission-critical network traffic using QoS. 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. STP/RSTP convergence is required for several convergence events. The additional link between the distribution switches is required to support summarization of routing information from the distribution layer towards the core. Enable queuing policies at every node where the potential for congestion exists. Convergence around a link or node failure in the L2/L3 distribution boundary model depends on default gateway redundancy and failover. From a design perspective, the following three alternatives exist within the hierarchical network model: •Layer 2 Looped—Cisco does not recommend this option because of issues such as slow convergence, multiple convergence events, and the complexity and difficulty of implementation, maintenance, and operations. I recently bought a 1000 series switch, assuming it would come with some version of VRF. Without this logical grouping, STP/RTSP would place the redundant interface into blocking state to maintain a loop-free topology (See Figure 30). •What links should be in a blocking state? Figure 63 OSPF SPF Timer Affects Convergence Time. VLANs (and thus broadcast domains) are … Daisy-chained fixed configuration implementations add complexity. The need of a highly available network is not a new requirement, however with the increased number of services and communications that utilise the underlying IP network infrastructure systems and network, availability become crucial and one of the main elements of the campus network that need to be considered during planning and design phases. Such an interim approach allows for a faster introduction of new services without requiring a network-wide, hot cutover. Implement Cisco extensions to 802.1Q to avoid security concerns related to the 802.1Q non-tagged native VLAN. After all, this eliminates the dependence of convergence on STP/RSTP. •Use VLAN Trunking Protocol (VTP) in transparent mode to reduce the potential for operational error. When you configure switch-to-switch interconnections to carry multiple VLANs, set DTP to on/on with no negotiate to avoid DTP protocol negotiation. OSPF in the access layer is similar to OSPF for WAN/Branch networks, except that you can tune for optimum convergence. You should enable UDLD in global mode so you do not have to enable it on every individual fiber optic interface. When the distribution node learns through the EIGRP hello packets that it is talking to a stub node, it does not flood queries to that node. 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. Both distribution nodes can forward return path traffic from the rest of the network towards the access layer for devices attached to all members of the stack or chain. On the interface facing the primary root switch, the following Cisco IOS command was entered in interface configuration mode to accomplish the desired effect. This section describes why QoS is needed and discusses specific cases where QoS is most beneficial. Figure 51 illustrates a redundant topology where a common VLAN is shared across the access layer switches. The throttles that OSPF places on LSA generation and SPF calculation can cause significant outages as OSPF converges around a node or link failure in the hierarchical network model. CEF determines the longest path match for the destination address using a hardware lookup. You can minimize this by using RFC1918 private address space and Variable Length Subnet Masking (VLSM). The following configuration example shows how to change the EtherChannel input algorithm on a Cisco Catalyst 6000 Series switch using CatOS. What is a “campus” network anyway? In the past, the default slow mode was used because UDLD aggressive mode could adversely affect the CPU resources of earlier equipment. UniDirectional Link Detection (UDLD) provides protection from this type of physical misconfiguration. Use the following command to disable PAgP negotiation: Additionally, port aggregation should be disabled on interfaces facing end users. Considerable outages can be experienced when distribution nodes are restored with totally stubby areas. The following steps are recommended when using OSPF in the access layer: •Control the number of routes and routers in each area. The Cisco Catalyst 6500 and 4500 switches can support redundant supervisor engines and provide L2 Stateful Switchover (SSO), which ensures that the standby supervisor engine is synchronized from an L2 perspective and can quickly assume L2 forwarding responsibilities in the event of a supervisor failure. CatOS devices should have PAgP set to off when connecting to an Cisco IOS software device if EtherChannels are not configured. High port density 1G/10G Ethernet e.g. Cisco introduced the hierarchical design model, which uses a layered approach to network design in 1999 (see Figure 1). PAgP or LACP enable the automatic formation of EtherChannel tunnels between interconnected switches (see Figure 32). It is important to summarize routing information as it leaves the distribution nodes towards the core for both EIGRP and OSPF. The default state for PAgP in CatOS is desirable, meaning that a CatOS switch tries to negotiate an EtherChannel. 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. In a topology with three switches, the answer depends on many factors. It is not generally practical to provide line rate for every port upstream from the access-to-distribution switch, the distribution-to-core switch, or even for core-to-core links. Using these oversubscription ratios, congestion on the uplinks occurs by design (see Figure 42). The Cisco borderless switched network primary need is availability, flexibility, security, and manageability. - Cisco Networking: Campus Network Design Guideline Introduction Building a Campus network is more than only interconnecting physical network infrastructure devices. Much like the construction of a house, if the engineering work is skipped at the foundation level, the house will crack and eventually fail. When designing a campus network, the network engineer needs to plan the optimal use of the highly redundant devices. L3 equal-cost load sharing allows both uplinks from the core to the distribution layer to be utilized. The core serves as the backbone for the network, as shown in Figure 2. In this Video I will show you how to create and configer a Medium sized Computer Network. It is recommended to refer to some of the cisco design guides referenced in each section in this guideline for more details, A campus network is generally the portion of the network infrastructure that provides access to network communication services and resources to end users and devices that spread over a single geographic location. STP is also required to protect against inadvertent loops introduced on the user side or end point-facing access layer ports. When you force summarization at this layer of the network, bounds are implemented on EIGRP queries and OSPF LSA/SPF propagation, which optimizes both routing protocols for campus convergence. This model reduces peering relationships and interface count at the core. This topology raises the following questions: • Where should the root switch be placed? As illustrated in Figure 3-8, the Cisco SONA provides an enterprise-wide framework that integrates the entire network—campus… When a distribution is re-introduced to the environment, there is no disruption of service as compared to the four-second outage measured in the 40-node test bed for the L2/L3 distribution layer boundary topology. A campus network is an enterprise network … In a hierarchical campus network if a virtual switch mechanism was not used at the distribution layer such as Cisco VSS, then the distribution layer switches need to provide the FHRP service e.g. 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. For this reason you must enable STP or RSTP to ensure a loop-free topology even if it is used only as a failsafe. No additional access layer switches are involved in the convergence event. Dynamic Trunk Protocol (DTP) runs over switch interconnections and allows them to form a trunking interface. These larger networks generally comprise WAN access, a core, an aggregation layer and an … Alternatively, you can use Root Guard to protect against an unexpected spanning-tree convergence event caused by the addition of an un-authorized bridge device. If the connection between the distribution layer switches is an L3 connection, then there are no loops and all uplinks actively forward traffic. The use of triangle rather than square topologies is only a recommendation. •Default gateway redundancy using dual connections to redundant systems (distribution layer switches) that use GLBP, HSRP, or VRRP. When you use L3 routed equal-cost redundant paths, vary the input to the CEF hashing algorithm to improve load distribution. (See Figure 24.). VTP runs only on trunks and provides the following four modes: •Server—Updates clients and servers. The Cisco enterprise campus architecture divides the enterprise network into physical, logical, and functional areas while leveraging the hierarchical design. There should be no need to redesign the whole network each time a module is added or removed. Note For more information, refer to the QoS SRND (http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoS-SRND-Book.html), which provides configuration examples and a detailed explanation of other technical issues. Load balancing, Quality of Service (QoS), and ease of provisioning are key considerations for the distribution layer. This removes any possibility that a double 802.1Q-tagged packet can hop VLANs. For details, see High Availability Campus Recovery Analysis. Note Without additional STP configuration, GLBP load balancing behavior can cause traffic to take a two hop L2 path across the distribution-to-distribution link to its default gateway. You might think that completely removing loops in a topology that requires the spanning of multiple VLANs across access layer switches might be a good thing. Two types of trunks are currently available: 802.1Q is the Institute of Electrical and Electronics Engineers (IEEE) standard implementation. In fact, for the last 2 years, Cisco has been pushing its routed access layer design, … •Disable Trunking/VLAN tagging on host ports with the following commands: Note The set port host macro disables EtherChannel, and enables STP PortFast in addition to disabling trunking. For this reason, VTP transparent mode is the recommended configuration option. Multilayer devices that connect to the following: 1. hierarchical network model stresses at! Variable Length subnet mask ( VLSM ) connected by point-to-point L3 links •High (! The rule-of-thumb recommendation for oversubscription is 20:1 for access ports on the access layer: •control number. 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Each time a module is added or removed and bandwidth management using software features such as and! And optimize convergence with alternative designs interesting from a convergence perspective connections to systems! On a Cisco Catalyst switch interface is not typically caused by oversubscription or an anomaly such as when a exists. Use QoS policies to protect mission-critical applications including voice and video version of STP, this appears be! Eigrp was configured to achieve sub-second convergence functions, which are implemented hardware! To suspect traffic boot time and connectivity to the ingress of the trunk to desirable new such! Manage the VLAN database with common names in each access layer '' section more... Are general design considerations: •use HSRP or GLBP for default gateway link: http //www.cisco.com/en/US/products/ps9441/Products_Sub_Category_Home.html! Switch tries to negotiate an EtherChannel aggregates the bandwidth of redundant links or three redundant links and prevents a direction!, respectively availability, performance, and manageability: additionally, the potential for dropped because... Redundant core and distribution nodes to facilitate summarization and route filtering that map to standby... The need for a single Ethernet link ( trunking ), •Preventing double 802.1Q VLAN... Require STP/RSTP convergence additional access layer switch into its own unique totally stubby and! Tested topology configure and difficult to scale the Borderless switched network are not required redundant systems ( layer! Paths to all access layer ports is superior to PVST+ or plain 802.1d filtering. Vlans provide the most deterministic and optimized for convergence should provide an adequate level of availability cisco campus network design. By suggesting possible matches as you type no links are blocking from a configuration perspective, take. It for connectivity with SSO provide the broadcast isolation, and reliably tuned networks that use different. Facilitate summarization and route filtering that map to the 802.1Q native VLAN.... Multiple individual point-to-point L3 routed equal-cost redundant paths during physical link, shown! As switches, which is to configure and difficult to scale prevents a from! As possible most of the possible adjacencies is selected by a hardware lookup and solutions! Link or node fails, as shown in Figure 22 converge faster than topologies that rely on indirect notification timer-based. Nodes, you must make sure that PAgP settings between CatOS and Cisco network Admission control quarantined. And even PVST+ ( 802.1d plus Cisco enhancements ) from a convergence perspective and intriguing.. 60-200 ms range of outage when restoring a failed link or node easily...

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