If you build a topology where VLANs are local to individual access layer switches, this type of problem is inconsequential because traffic is only flooded on one interface (the only interface in the VLAN) on the standby HSRP, VRRP, or non-forwarding GLBP peer. 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. This alternating approach eliminates the always right or always left biased decisions and helps balance the traffic over equal-cost redundant links in the network (see Figure 17). From the perspective of the access layer, at least three sets of redundant links are traversed to another building block, such as the data center. 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). The distribution layer provides default gateway redundancy using the Gateway Load Balancing Protocol (GLBP), Hot Standby Router Protocol (HSRP), or Virtual Router Redundancy Protocol (VRRP). Return path traffic for the same convergence event in this topology is shown in Figure 56. The difference between a WAN router and a campus switch is the number of interfaces and the amount of memory associated with each. Figure 51 illustrates a redundant topology where a common VLAN is shared across the access layer switches. The backup peer assumes the virtual MAC of the device that has failed and begins forwarding traffic for its failed peer. HSRP. I recently bought a 1000 series switch, assuming it would come with some version of VRF. •Only span VLANs across multiple access layer switches if you must. This chapter from Cisco Press provides an overview of the technologies available today to design networks. Use the following command to disable PAgP negotiation: Additionally, port aggregation should be disabled on interfaces facing end users. The principal advantages of this model are its hierarchical structure and its modularity. Channel executives said Cisco’s new campus networking approach offers software-defined networking, management and security capabilities, but will face a customer adoption test. Routing protocols are utilized in a hierarchical network design to reroute around a failed link or node. … For optimum core layer convergence, build triangles, not squares, to take advantage of equal-cost redundant paths for the best deterministic convergence. What is a “campus” network anyway? If VLANs span across multiple access layer switches, return path traffic can be flooded to all access layer switches and end points. number of L3 hopes and expected future growth, Convergence time e.g. VPTv3 contains many enhancements for security and reliability. When the algorithm was changed to include L4 information, nearly full utilization was achieved with the same topology and traffic pattern (see Figure 31). Now I want to power off the standby switch so that we can reuse it other new location. If you build a topology using triangles, with equal-cost paths to all redundant nodes, you can avoid timer-based, non-deterministic convergence. When EIGRP is used as the routing protocol for a fully routed or routed access layer solution, take the following EIGRP tuning and best practice steps to achieve sub-200 ms convergence: •Summarize towards the core from the distribution layer. The solution to this problem is to provide alternate connectivity across the stack in the form of a loopback cable running from the top to the bottom of the stack, as shown in Figure 48. You can create channels containing up to eight parallel links between switches. •Security services for additional security against unauthorized access to the network through the use of tools such as 802.1x, port security, DHCP snooping, Dynamic ARP Inspection, and IP Source Guard. When considering core topologies, it is important to consider the benefits of topologies with point-to-point links. •Tune EtherChannel and CEF load balancing to ensure optimum utilization of redundant, equal-cost links. Cisco SONA Framework. Get validated design guidance on our open, software-driven approach to deploy a digital-ready network. The campus network, as defined for the purposes of the enterprise design guides, consists of the integrated elements that comprise the set of services used by a group of users and end … •Default gateway redundancy using dual connections to redundant systems (distribution layer switches) that use GLBP, HSRP, or VRRP. Common Campus network Hierarchical Design Models Cisco’s hierarchical network design model breaks the complex problem of network design into smaller and more manageable. 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. A routing protocol can even achieve better convergence results than the time-tested L2/L3 boundary hierarchical design. The rule-of-thumb recommendation for oversubscription is 20:1 for access ports on the access-to-distribution uplink. 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. When connecting a Cisco IOS software device to a CatOS device, make sure that PAgP settings are the same on both sides. The enterprise campus architecture can be applied at the campus scale, or at the building scale, to allow flexibility in network design and facilitate ease of implementation and troubleshooting. •Set hello and dead timers to 1 and 3, respectively. Considerable outages can be experienced when distribution nodes are restored with totally stubby areas. As illustrated in Figure 3-8, the Cisco SONA provides an enterprise-wide framework that integrates the entire network—campus… As campus network planners begin to consider migration to dual stack IPv4/IPv6 environments, migrate to controller-based WLAN environments, and continue to integrate more sophisticated Unified Communications services, a number of real challenges lay ahead. STP is required to ensure a loop-free topology and to protect the rest of the network from problems created in the access layer. Great, thanks for sharing @Marwan ALshawi, Thanks to all your participation in the Community Helping Community, we have achieved our goal. When it comes to redundancy, however, you can have too much of a good thing. Only use L2 looped topologies if it cannot be avoided. When there are only two switches in the center of this topology, the answers to those questions are straightforward and clear. In most cases, VLANs are defined once during switch setup with few, if any, additional modifications to the VLAN database in an access layer switch. L3 equal-cost load sharing allows both uplinks from the core to the distribution layer to be utilized. This can be most easily accomplished by changing the port cost on the interface between the distribution layer switches on the STP secondary root switch. Cisco has developed the Hot Standby Router Protocol (HSRP) to address this need, and the IETF subsequently ratified Virtual Router Redundancy Protocol (VRRP) as the standards-based method of providing default gateway redundancy. Two types of trunks are currently available: 802.1Q is the Institute of Electrical and Electronics Engineers (IEEE) standard implementation. In Figure 46, an L3 connection exists between the distribution nodes. For the remainder of this document, the term EtherChannel is used to describe both variants. There are quite a few spelling errors. New technologies such as 802.1x and VLAN assignment and Cisco Network Admission Control with quarantined VLAN, must be used with transparent mode. However, some additional complexity (uplink IP addressing and subnetting) and loss of flexibility are associated with this design alternative. The flowing three major network resiliency requirements as described by Cisco Borderless design guide 1.0 cover most of the common types of failure conditions. Implement Cisco extensions to 802.1Q to avoid security concerns related to the 802.1Q non-tagged native VLAN. It is therefore recommended that only links intended for transit traffic be used to establish routing neighbor or peer relationships. When HSRP or VRRP are used to provide default gateway redundancy, the backup members of the peer relationship are idle, waiting for a failure event to occur for them to take over and actively forward traffic (see Figure 36). When using the on/on setting, PAgP is not enabled on members of the bundle. 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. 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. Cisco switches let you tune the hashing algorithm used to select the specific EtherChannel link on which a packet is transmitted. Figure 7 Potential Single Points of Failure. However, fully-routed access layer designs are not often deployed today. When implementing this topology, be aware that when the primary HSRP peer comes back online and establishes its L3 relationships with the core, it must ARP for all the end points in the L2 domain that it supports. While PVST+, Rapid PVST+, and EIGRP all converged in less than one second (EIGRP in sub 200 ms), OSPF required at least 1.65 seconds to converge around this specific failure. The default state for PAgP in CatOS is desirable, meaning that a CatOS switch tries to negotiate an EtherChannel. 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. The hierarchical network model stresses redundancy at many levels to remove a single point of failure wherever the consequences of a failure are serious. 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. Tuning of Cisco Express Forwarding (CEF) equal-cost path selection is required to prevent CEF polarization, in which redundant links may be underutilized. The design principles and implementation best practices described in this document are tried-and-true lessons learned over time. CEF determines the longest path match for the destination address using a hardware lookup. A campus network is an enterprise network … The defaults are different. If the connection between the distribution layer switches is an L3 connection, then there are no loops and all uplinks actively forward traffic. The following configuration snippets illustrate the OSPF configuration: The design recommendations described in this design guide are best practices designed to achieve the best convergence possible. Figure 39 GLBP, HSRP, and VRRP Test Results. 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. CEF is a deterministic algorithm. •Routed Access—This option is interesting from a convergence performance perspective, but is not yet widely deployed. In addition, the high port count adds unnecessary cost and increases complexity as the network grows or changes. This redundant L3 peering has no benefit from an HA perspective, and only adds load in terms of memory, routing protocol update overhead, and complexity. Internet worms and denial of service (DoS) attacks have the ability to flood links even in a high-speed campus environment. 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. This can result in a bridge between a wireless LAN interface and an Ethernet interface, or between two Ethernet interfaces. Additionally, Cisco switch operating software can now tag all native VLAN traffic. Figure 21 PVST+ and Rapid PVST+ Performance. Operational resiliency: Enables resiliency capabilities to the next level, providing complete network availability even during planned network outages using In Service Software Upgrade (ISSU) features. 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. This section describes the foundation technologies used in the campus network and the recommended configurations. Figure 62 Primary Distribution Node Restoration. Figure 41 GLBP with STP Blocking Distribution-to-Distribution Link. Virtual Trunk Protocol (VTP) is a protocol that allows network managers to centrally manage the VLAN database. This design is less than optimal from a convergence perspective. Protecting against double failures by using three redundant links or three redundant nodes in the hierarchical design does not increase availability. If you have a routed access layer design, redundant supervisors with NSF with SSO provide the most benefit. This allows for the failure or removal of one of the distribution nodes without affecting end point connectivity to the default gateway. Figure 61 Distribution-to-Access Link Failure. Police unwanted traffic flows as close to their sources as possible. For this reason, VTP transparent mode is the recommended configuration option. To achieve this, use the mls ip cef load-sharing full command on the distribution nodes. However, the other extreme is also a bad thing. •Traffic is dropped until the MaxAge timer expires and until the listening and learning states are completed. Use the CatOS set port host or the Cisco IOS software switchport host commands to disable trunking and EtherChannel, and to enable STP PortFast. Networking for a medium campus is designed for high availability, performance, and manageability. The Cisco Enterprise Architecture extends the concept of hierarchy from the original two modules: Campus and WAN. UNICEF will be happy. •Use Rapid PVST+ to protect against user-side loops. Distinct building blocks can be put in-service and taken out-of-service without impacting the rest of the network. •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. As stated earlier, this problem only occurs in a topology where VLANs span multiple access layer switches in a large L2 domain. ISL does consume a small amount of additional bandwidth because of the double CRC check that it performs. In the core layer, leave the default, which is to use only L3 information. For example, by default, the Windows XP Home Networking Wizard bridges together all the interfaces on the machine. STP lets the network deterministically block interfaces and provide a loop-free topology in a network with redundant links (see Figure 18). 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. This is a benefit, however it makes this design less flexible than other configurations. The access layer is the first point of entry into the network for edge devices, end stations, and IP phones (see Figure 5). If you do not disable EtherChannel negotiation, then the mismatch between the default states of CatOS and Cisco IOS software can cause as much as seven seconds of loss during link negotiation, as shown in Figure 33. Before the development of GLBP, methods used to utilize uplinks more efficiently were difficult to implement and manage. Those questions are straightforward and clear more '' approach should be used normally, so both uplinks available! For unexpected behavior due to operational error single physical link failures, such as link Aggregation ( EtherChannel or )! 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