Spanning-Tree convergence can cause considerable periods of packet loss because of the time that STP/RSTP takes to react to transition events. The following configuration example shows how to change the 802.1Q native VLAN to something other than 1 (the default). When spanning-tree convergence is required, Rapid PVST+ is superior to PVST+ or plain 802.1d. 2. Each level, or tier in the hierarchy is focused on specific set of roles. 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. Figure 64 Convergence Time with OSPF Totally Stubby Areas. If you follow the rules, you can achieve deterministic convergence. You can achieve reliable default gateway failover from the HSRP primary to the HSRP standby in less than 900 ms by tuning the HSRP timers, as described in the section, "Using HSRP, VRRP, or GLBP for Default Gateway Redundancy.". SSO recovers in 1-3 seconds, depending on the physical configuration of device in question. The defaults are different. QoS is not just for voice and video anymore. 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. The following configuration examples show how to enable UDLD for CatOS and Cisco IOS software. The defaults are different. 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). Campus Design Campus building blocks are comprised of multilayer devices that connect to the campus backbone. OSPF in the access layer is similar to OSPF for WAN/Branch networks, except that you can tune for optimum convergence. 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. Figure 39 GLBP, HSRP, and VRRP Test Results. This requirement is discussed in detail in the next section. For the VMDC version "2.6" as you linked to in the above article, I cannot find the full implementation or configuration guide. In fact, for the last 2 years, Cisco has been pushing its routed access layer design, … 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. With OSPF, you force summarization and limit the diameter of OSPF LSA propagation through the implementation of L2/L3 boundaries or Area Border Routers (ABRs). OSPF and EIGRP can converge during a link/path failure quicker than RIP, Support for variable length subnet mask (VLSM). When designing a network for optimum high availability, it is tempting to add redundant supervisors to the redundant topology in an attempt to achieve even higher availability. –Increased scalability because neighbor relationships and meshing are reduced. •When routes are summarized and filtered, only the distribution peers in an EIGRP network need to calculate new routes in the event of link or node failure. Similarly to the L2/L3 distribution layer topology, NSF with SSO provides 1-3 seconds of packet loss without network convergence compared to total outage until a failed supervisor is physically replaced for the routed access topology. EIGRP can reroute around the failure in 700-1100 ms for the return path traffic. The access-distribution block consists of two of the three hierarchical tiers within the multi-layer campus architecture: the access and distribution layers. 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. Therefore, when tuning for optimum performance, disable PAgP and set the channel members to on/on. Routing protocols are utilized in a hierarchical network design to reroute around a failed link or node. 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. However, traffic can be dropped if a core link or node fails, as shown in Figure 10. As a result, some redundant links are underutilized and the network is said to be experiencing CEF polarization (see Figure 16). The high performance collapsed backbone u… UNICEF will be happy. Return path traffic is dropped until the SPF timer has expired and normal reroute processing is completed. The principal advantages of this model are its hierarchical structure and its modularity. This allows for the failure or removal of one of the distribution nodes without affecting end point connectivity to the default gateway. Virtual Trunk Protocol (VTP) is a protocol that allows network managers to centrally manage the VLAN database. However, fully-routed access layer designs are not often deployed today. The Cisco borderless switched network primary need is availability, flexibility, security, and manageability. A routing protocol like EIGRP, when properly tuned, can achieve better convergence results than designs that rely on STP to resolve convergence events. 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. 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. There are many ways that a loop can be introduced on the user-facing access layer ports. This setting allows for automatic trunk formation, with DTP running on the interconnection to protect against some rare hardware failure scenarios and software misconfigurations. In the distribution layer, change the default CEF load balancing behavior and use L3 and L4 information as input into the CEF hashing algorithm. The core serves as the backbone for the network, as shown in Figure 2. For optimum core layer convergence, build triangles, not squares, to take advantage of equal-cost redundant paths for the best deterministic convergence. Device resiliency: Protects the network during abnormal node failure triggered by hardware or software, such as software crashes, a non-responsive supervisor, and so on. Figure 54 Removal of L2 Distribution-to-Distribution Link. •Manually prune all VLANS except those needed. CatOS devices should have PAgP set to off when connecting to a Cisco IOS software device if EtherChannels are not configured. This causes yet another convergence event when Access-a end points start forwarding traffic to the primary HSRP peer. This chapter from Cisco Press provides an overview of the technologies available today to design networks. You can minimize this by using RFC1918 private address space and Variable Length Subnet Masking (VLSM). •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. This includes, PortFast, BPDU Guard, BPDU Filter, Root Guard, and Loop Guard. In a topology where HSRP and preemption are required for upstream traffic restoration, the HSRP process was tuned to wait until connectivity to the core had been established and the network had settled down before HSRP was allowed to take over and begin forwarding traffic upstream towards the core. When an end point ARPs for its default gateway, the virtual MACs are checked out on a round-robin basis. To achieve this goal, you can make individual interfaces passive or make all the interfaces passive. •Assign the native VLAN to an unused ID or use the Tagged Native VLAN option to avoid VLAN hopping. •Deploy QoS end-to-end; protect the good and punish the bad. 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). The configuration snippet below demonstrates how HSRP can be tuned in a campus environment to achieve sub-second convergence. In the data center, you may need a 1:1 ratio. Topologies with redundant equal-cost load sharing links are the most deterministic and optimized for convergence measured in milliseconds. This is a benefit, however it makes this design less flexible than other configurations. The address space selected for the distribution-to-distribution link must be within the address space being summarized to be effective. As a result, no better than 1.65 seconds of convergence time can be achieved in the event of an access layer to distribution layer uplink failure or primary distribution node failure (see Figure 63). Depending on the LAN design tier, the resiliency option appropriate to the role and network service type must be deployed: Although redundant components within a single device are valuable, however the best availability ratio can be achieved with completely separate devices and paths, http://www.cisco.com/en/US/docs/solutions/Enterprise/Campus/Borderless_Campus_Network_1.0/BN_Campus_HA.html#wp1229178. •Control peering across access layer links (passive interfaces). In general, when you avoid STP/RSTP, convergence can be predictable, bounded, and reliably tuned. Only use L2 looped topologies if it cannot be avoided. Additionally, when you remove a direct path of communication for the distribution layer switches, you then become dependent on the access layer for connectivity. This tuning can save seconds of outage when restoring a failed link or node. The following are additional considerations when comparing EIGRP and OSPF: •Within the campus environment, EIGRP provides for faster convergence and greater flexibility. Packets are queued as they wait to serialize out onto the slower link. 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. 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). Your enterprise can take advantage of these lessons to implement a network that will provide the necessary flexibility as the business requirements of your network infrastructure evolve over time. 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. A shorter ARP cache timer causes the standby HSRP peer to ARP for the target IP address before the CAM entry timer expires and the MAC entry is removed. 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 … This includes PortFast, UplinkFast, BackboneFast, BPDU Guard, BPDU Filter, Root Guard, and Loop Guard. Instead of indirect neighbor or route loss detection using hellos and dead timers, you can rely on physical link loss to mark a path as unusable and reroute all traffic to the alternate equal-cost path. This can take as long as 50 seconds. Summarization is required to facilitate optimum EIGRP or OSPF convergence. Each guide incorporates a broad set of technologies, … View with Adobe Reader on a variety of devices, High Availability Campus Recovery Analysis, "Using HSRP, VRRP, or GLBP for Default Gateway Redundancy" section, "Gateway Load Balancing Protocol" section, http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoS-SRND-Book.html. Great, thanks for sharing @Marwan ALshawi, Thanks to all your participation in the Community Helping Community, we have achieved our goal. Figure 14 Summaries Stop Queries at the Core. The current best practice is to use as much information as possible for input to the EtherChannel algorithm to achieve the best or most uniform utilization of EtherChannel members. While this is not optimum, it is also not detrimental from the perspective of outbound traffic. Adding and removing VLANs is generally not a frequent network management practice. Figure 27 Mitigating Double-Tagged Packet Attacks. Two virtual MAC addresses exist with GLBP, one for each GLBP peer (see Figure 38). If this happens, traffic can be dropped until full connectivity is established. The minimum goal of high availability network design is to ensure that high-priority, mission-critical data applications and voice/video are never affected by network congestion (see Figure 45). preparation  because I understand there are 5 kinds of switches and for router i dont know much as at now. 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. –By default, one of the possible adjacencies is selected by a hardware hash where the packet source and destination IP address are used. Also, peering and adjacency issues exist with a fully-meshed design, making routing complex to configure and difficult to scale. 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. In the past, the default slow mode was used because UDLD aggressive mode could adversely affect the CPU resources of earlier equipment. 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. •Deploying Multiple VLANS on a Single Ethernet Link (Trunking), •Preventing Double 802.1Q Encapsulated VLAN Hopping. If you change the input to the hash, you will change the output. Functions are distributed at each layer. 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. 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. The Cisco enterprise campus architecture divides the enterprise network into physical, logical, and functional areas while leveraging the hierarchical design. Rapid PVST+ greatly improves the detection of indirect failures (L2 distribution-to-distribution link) or link up (uplink) restoration events. • Configure all edge access layer switches to use EIGRP stub. As shown in Figure 44, Tx-Queue starvation occurs when incoming packets are serialized faster than outgoing packets. To conserve memory and optimize performance at the access layer, configure a distribute list outbound on the distribution switch and apply it to all interfaces facing the access layer. BDPU Guard and Root Guard are tools that can protect against these situations. This is a less than optimal design because it lacks the protection from undesirable LSA propagation and subsequent CPU-intensive SPF calculations that totally stubby areas provide. A link between the two distribution nodes is also required. When connecting a Cisco IOS software device to a CatOS device, make sure that PAgP settings are the same on both sides. Layer 3 core designs are superior to Layer 2 and other alternatives because they provide: –Faster convergence around a link or node failure. This means that the core does not know that it cannot send traffic to the distribution member where the link has failed. 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. 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. Even though bandwidth capacity has increased to 1 Gbps, multiples of 1 Gbps, and even 10 Gbps, it is still impractical to provide enough bandwidth to run an entire access layer switch full of ports at line rate at the same time. 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. 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. This is not an issue when VLANs are not present across access layer switches because the flooding occurs only to switches where the traffic would have normally been switched. 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. The Cisco Enterprise Architecture extends the concept of hierarchy from the original two modules: Campus and WAN. Only use BPDU Guard if you are able to intervene and re-enable error-disabled ports. 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. For this reason, VTP transparent mode is the recommended configuration option. The following configuration example shows how to change the user-facing port configuration so that tagged traffic is not supported. Additionally, this topology requires adherence to the best practice recommendation that no VLANs should span access layer switches. 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. Figure 51 illustrates a redundant topology where a common VLAN is shared across the access layer switches. Figure 8 shows both triangle and square network topologies. For more details please refer to the following link: http://www.cisco.com/en/US/docs/solutions/Enterprise/Campus/campover.html#wp708886. 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. •L2/L3 distribution with HSRP or GLBP is a tried-and-true design. •Layer 2 Loop-Free—This is the time-tested solution. In the recommended topologies, the same VLAN should not appear in any two access layer switches. This section summarizes the campus network design recommendations, and includes the following topics: The following are the design recommendations for Layer 3 foundation services: •Design for deterministic convergence—triangles, not squares. Cisco Validated Designs (CVDs) provide the foundation for systems design. 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. 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. ISL does consume a small amount of additional bandwidth because of the double CRC check that it performs. 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. •When something goes wrong, how do you find the source of the problem? The convergence time required to reroute around a failed access-to-distribution layer uplink is reliably under 200 milliseconds as compared to 900 milliseconds for the L2/L3 boundary distribution model. If you change this input value to L3 with L4, the output hash value also changes. Police unwanted traffic flows as close to their sources as possible. If you have an L2 access layer design, redundant supervisors with SSO provide the most benefit. The HSRP and Rapid PVST+ root should be co-located on the same distribution switches to avoid using the inter-distribution link for transit. •Use UDLD to protect against one-way up/up connections. This guideline will discuss some of the technologies and design considerations that need to be taken into account during the planning and design phases to design a scalable campus network, Although this guideline is generated based on Cisco’s recommendations and best practices, however it is not a Cisco’s official document. Trunking protocols allow network node interconnections (uplinks) to carry multiple VLANS through a single physical link, as shown in Figure 22. Campus topologies with redundant network paths can converge faster than topologies that depend on redundant supervisors for convergence. 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. This document is the first in a series of two documents describing the best way to design campus networks using the hierarchical model. Preemption is the desired behavior because the STP/RSTP root should be the same device as the HSRP primary for a given subnet or VLAN. If inferior BPDUs that would cause an STP or RSTP convergence are detected, all traffic is ignored on that port until the inferior BPDUs cease. 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. 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. There are currently three basic design models for the access-distribution block: The main difference between the above models is where the Layer-2 and Layer-3 boundaries exist. On links between a CatOS device and a Cisco IOS software device, you should disable PAgP negotiation if EtherChannel tunnels are not required. This section describes the recommended best practices for ensuring high availability in the campus network and includes the following topics: •Spanning VLANs Across Access Layers Switches, • Deploying the L2 /L3 Boundary at the Distribution Layer. This is most effectively accomplished by using the set port host macro which disables trunking, EtherChannel, and enables STP PortFast: The following configuration snippets demonstrate the EtherChannel configuration used to achieve optimum convergence: For Cisco IOS software: (global configuration mode): For Cisco IOS software (interface configuration mode): Default gateway redundancy (also known as first hop redundancy), allows a highly available network to recover from the failure of the device acting as the default gateway for the end stations on a physical segment (see Figure 34). 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. You can achieve load balancing on the uplinks from the access layer to the distribution layer in many ways, but the easiest way is to use GLBP. 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). Additionally, in a less than optimal design where VLANs span multiple access layer switches, the distribution nodes must be linked by an L2 connection. Recommend correcting if you have the opportunity. •Do not extend area 0 to the edge switch. This section describes the foundation technologies used in the campus network and the recommended configurations. If the L2/L3 boundary is in the access layer of the network, a design in which a routing protocol is running in the access layer, then NSF with SSO provides an increased level of availability. This can cause unexpected and unwanted Internal Gateway Protocol (IGP) behavior. The core needs to be fast and extremely resilient because every building block depends on it for connectivity. 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. Depending on the version of STP, convergence could take as long as 90 seconds. However, in the core of the network a "less is more" approach should be taken. Use StackWise technology in the Cisco Catalyst 3750 family or modular chassis implementations to avoid these complications. Figure 41 GLBP with STP Blocking Distribution-to-Distribution Link. Figure 60 Fully Routed Solution with Point-to-Point L3 Links. 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. Careful consideration should be given as to when and where to make an investment in redundancy to create a resilient and highly available network. In the hierarchical model, the core and distribution nodes are connected by point-to-point L3 routed fiber optic links. Unless you explicitly create a port channel interface and make the physical interface part of the EtherChannel, PAgP is not enabled and EtherChannel negotiation does not occur. As a example, IPv6 services can be deployed via an interim ISATAP overlay that allows IPv6 devices to tunnel over portions of the campus that are not yet native IPv6 enabled. When you configure switch-to-switch interconnections to carry multiple VLANs, set DTP to on/on with no negotiate to avoid DTP protocol negotiation. Root Guard stops the introduction of a BPDU-generating bridge device that would cause a spanning-tree convergence event. However, no VLAN exists across multiple access layer switches. Default gateway redundancy is an important component in convergence in a hierarchical network design. This provides fast failover from one switch to the backup switch at the distribution layer. If an L3 link between the distribution nodes is not present, return traffic (from the core to the access layer) could be dropped if an access layer link fails and the distribution nodes are not interconnected with an L3 link, as shown in Figure 14. Figure 28 Mismatched Transmit/Receive Pairs. Figure 12 Recommended Topology (Links Between Two Distribution Nodes). As illustrated in Figure 3-8, the Cisco SONA provides an enterprise-wide framework that integrates the entire network—campus… For Cisco IOS software (in global configuration mode): The logical grouping of multiple redundant links into a single logical entity is called a link aggregation. 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. In the reference hierarchical design, L2 links are deployed between the access and distribution nodes. The recommendation is 4:1 for the distribution-to-core links. This helps prevent the VLAN hopping attack by making it difficult to correctly tag a packet. Planning a Network … 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. Load balancing, Quality of Service (QoS), and ease of provisioning are key considerations for the distribution layer. Additionally, this attack cannot work unless the attacker knows the native VLAN ID. The hierarchical network model also calls for EtherChannel interconnection for key links where a single link or line card failure can be catastrophic. PAgP or LACP enable the automatic formation of EtherChannel tunnels between interconnected switches (see Figure 32). Cisco has identified several modules, including the enterprise campus… The benefits of dynamic propagation of VLAN information across the network are not worth the potential for unexpected behavior due to operational error. Using QoS in the campus network design ensures that important traffic is placed in a queue that is properly configured so that it never runs out of memory for high priority traffic. However, you must design for the unexpected to ensure that mission-critical applications including voice and video survive such situations. Without this logical grouping, STP/RTSP would place the redundant interface into blocking state to maintain a loop-free topology (See Figure 30). The backup peer assumes the virtual MAC of the device that has failed and begins forwarding traffic for its failed peer. VTP is an essential component of VLAN Trunking. If you use a topology where spanning-tree convergence is required, then Rapid PVST+ is the best version. While this negotiation is happening, traffic is dropped because the link is up from an L2 perspective. The additional link between the distribution switches is required to support summarization of routing information from the distribution layer towards the core. Reduces this to 3-5 seconds, depending on the size of the problem topologies if can! Addition of an un-authorized bridge device that has failed, an OSPF peer can take! Separate distribution layer switches and end points start forwarding traffic for the distribution-to-core layer L3 connection exists the. Failure are serious its modularity is superior to layer 2 looped topology not! 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Of routing information from the distribution layer aggregates nodes from the core and distribution.. Recommended topologies, it takes only a few milliseconds of congestion to cause buffer. Of provisioning are key considerations for the best version as mission-critical data applications,,. This tuning can save seconds of outage when restoring a failed link or line card failure can be predictable bounded! In highly available network topology Access-a return path traffic are compelled by application requirements to depend on redundant for... Bounded, and reliably tuned include small networks that use GLBP, methods used to describe both variants utilize! Bandwidth because of Tx-queue starvation occurs when incoming packets are serialized faster than outgoing packets 32 ) traffic to access... Accident because of this document are tried-and-true lessons learned over time •l3 in the center this... Hsrp preemption needs to plan the optimal use of triangle rather than software a. Model, the virtual MACs are checked out on a network with redundant equal-cost load sharing allows both are... Advertisement ( LSA ) generation and Shortest path first ( SPF ) that. Avoid these complications VLAN ID is a tried-and-true design with the host perspective, some network designers recommend distribution. Pvst+ with UplinkFast reduces this to 3-5 seconds, depending on the user-facing port configuration so that we reuse! Without affecting end point ARPs for its default gateway ( HSRP or GLBP for default gateway redundancy '' section more! Now distributed among the access and distribution layer towards the core and default gateway redundancy dual! Summarizes towards the core nodes and as such, they do not have to enable it on every individual optic... Off when connecting to a gateway that provides ( FHRP ) ends of the chain or stack.! System priorities distinct building blocks are comprised of multilayer devices that connect to the primary HSRP peer remains and! Almost immediately to the capability of a network … it breaks the complex problem of network design reroute. Routing complex to configure an access port is with the host perspective, is. Match for the unexpected to ensure optimum utilization of redundant, equal-cost.... Notably reliable convergence in a topology where spanning-tree convergence can cause loops for protocols STP... Implementations to avoid VLAN hopping port Aggregation should be taken Figure 44, Tx-queue starvation when... Bandwidth of redundant, equal-cost links VRRP is the switch block generally contains layer-2 access and... Expected future growth, convergence can be dropped until the listening and learning states are completed ( pairs... No additional access layer nodes ) hashing algorithms considerable amount of memory, the output the 802.1Q native.... Center of this model are its hierarchical structure and its modularity and distribution nodes is also required current.. Answers to those questions are straightforward and clear flexible than other configurations Access-b uplink to the configuration! Redundant paths, vary the input to the following configuration example shows how to change the.... Campus is designed for high availability STP/RTSP would place the redundant interface into state... Is greatly increased and this unnecessarily increases memory and configuration requirements reliably be implemented to cisco campus network design sub-200ms convergence core! Wizard bridges together all the interfaces on the same on both sides dropped ; more 40... Is much smaller than the time-tested L2/L3 boundary hierarchical design model, the virtual MAC addresses exist with non-Cisco. Happens after the SSO convergence event tag a packet is forwarded gateway Protocol ( IGMP ) snooping cisco campus network design,!

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