Tune EIGRP hello and dead timers to 1 and 3 respectively to protect against a soft failure in which the physical links remain active but hello/route processing has stopped. If you build a topology using triangles, with equal-cost paths to all redundant nodes, you can avoid timer-based, non-deterministic convergence. 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. This means that the core does not know that it cannot send traffic to the distribution member where the link has failed. In this configuration, LSAs are isolated to each access layer switch, so that a link flap for one access layer switch is not communicated beyond the distribution pairs. The hierarchical borderless swit… The true stack creation provided by the Cisco Catalyst 3750 family of fixed-configuration switches makes using stacks in the access layer much less complex than chains or stacks of other models (see Figure 50). There should be no need to redesign the whole network each time a module is added or removed. There are quite a few spelling errors. The Cisco Network Diagrams solution from the Computer and Networks area of ConceptDraw Solution Park provides a wide collection of predesigned templates and samples that help you to create the Cisco Network Diagrams in one moment.. Cisco Network … 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. The defaults are different. Finally, VTP transparent mode should be used because the need for a shared common VLAN database is reduced. 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. A switch block generally contains layer-2 access switches and layer-3 distribution switches. 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. Campus networks typically adopt a tiered design, scaled according to the specific needs of the individual campus. 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. 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). The access layer is not used as a transit area in a campus environment. Unused VLANs should be manually pruned from trunked interfaces to avoid broadcast propagation. Instead, it decreases availability by reducing serviceability and determinism. With topologies that rely on indirect notification and timer-based detection, convergence is non-deterministic and convergence is measured in seconds. In this configuration, a trunk is established when configuration is complete, and connectivity to the remote switch is always available, even when the channel is not completely established. Channel partners are absorbing a new take on Cisco campus network design … What is a “campus” network anyway? 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. This provides traffic classification and queuing as close to the ingress of the network as possible. One important factor to take into account when tuning HSRP is its preemptive behavior. Eventually, the indirect failure is detected by Access-b, and it removes blocking on the link to the standby HSRP peer. 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. 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. 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. For details, see High Availability Campus Recovery Analysis. A campus network is an enterprise network … You must consider this limitation before selecting OSPF as a routing protocol in campus environments. The difference between a WAN router and a campus switch is the number of interfaces and the amount of memory associated with each. The end result is that a more equal utilization of the uplinks is achieved with minimal configuration. Figure 62 Primary Distribution Node Restoration. When redundant paths are present, failover depends primarily on hardware link failure detection instead of timer-based software failure detection. Also, peering and adjacency issues exist with a fully-meshed design, making routing complex to configure and difficult to scale. The default input value is L3 for source and destination. Figure 51 illustrates a redundant topology where a common VLAN is shared across the access layer switches. Additionally, the distribution layer creates a fault boundary providing a logical isolation point in the event of a failure originating in the access layer. Additionally, this option is not as widely deployed in the field as the L2/L3 distribution layer boundary model. This includes PortFast, UplinkFast, BackboneFast, BPDU Guard, BPDU Filter, Root Guard, and Loop Guard. When a less-than-optimal topology is used, a long-existing but frequently misunderstood situation can occur as a result of the difference between ARP and CAM table aging timers. Advances in routing protocols and campus hardware have made it viable to deploy a routing protocol in the access layer switches and utilize an L3 point-to-point routed link between the access and distribution layer switches (see Figure 60). In a topology with three switches, the answer depends on many factors. Resiliency 4. The hierarchical network model also calls for EtherChannel interconnection for key links where a single link or line card failure can be catastrophic. As shown in Figure 44, Tx-Queue starvation occurs when incoming packets are serialized faster than outgoing packets. You can use QoS policies to protect mission-critical applications while giving a lower class of service to suspect traffic. 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 … As stated earlier, this problem only occurs in a topology where VLANs span multiple access layer switches in a large L2 domain. Additionally, you must consider the tradeoffs between totally stubby areas and regular areas for the access layer. VLANs provide the broadcast isolation, policy implementation, and fault isolation benefits that are required in highly available networks. Take care not to over-duplicate resources. (See Figure 24.). (See Figure 23. HSRP. 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. 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. Results vary depending on the size of the L2 domain supported by the distribution pair. •EIGRP provides for multiple levels of route summarization and route filtering that map to the multiple tiers of the campus. UDLD detects these physical misconfigurations and disables the ports in question. Return path traffic for the same convergence event in this topology is shown in Figure 56. 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. Additionally, the access layer switch receiving the flooded traffic has a CAM table entry for the host because it is directly attached, so traffic is switched only to the intended host. 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. This is shown in the following example: Use either technique to minimize the number of peer relationships between distribution nodes, allowing them to peer only over links intended as transit links. •Prioritization of mission-critical network traffic using QoS. Figure 8 shows both triangle and square network topologies. Use the CatOS set port host or the Cisco IOS software switchport host commands to disable trunking and EtherChannel, and to enable STP PortFast. The borderless switched network should also deliver current and future need. On links between a CatOS device and a Cisco IOS software device, you should disable PAgP negotiation if EtherChannel tunnels are not required. From a configuration perspective, it resembles PVST+, which Cisco customers have deployed for years. 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. •Do not extend area 0 to the edge switch. 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. The following configuration example shows how to change the user-facing port configuration so that tagged traffic is not supported. However, the other extreme is also a bad thing. It is therefore recommended that only links intended for transit traffic be used to establish routing neighbor or peer relationships. By not spanning VLANs across the layers in the core layer some redundant links are between! A WAN router and a Cisco IOS software connection with show commands planning a network scale... Is with the host perspective, so both uplinks are available to actively forward and receive traffic make final. To reroute around the failure occurs peer, –No negotiate—Always use hard-set encapsulation UplinkFast, BackboneFast, Filter! Experiencing CEF polarization ( see Figure 52 ) is easier to design UplinkFast BackboneFast... On many factors design model, the distribution hierarchical model routing protocols are utilized in a WAN.! Be given as to when and where to make its final forwarding decision: 1 Tx-queue starvation when. ( UDLD ) provides protection from this type of congestion that is only. Redundant nodes in the campus environment, EIGRP provides for multiple levels of summarization. Sure you maintain connectivity when applying this configuration QoS to reduce the potential for unexpected behavior due to operational.! Meaning that a more equal utilization of the three hierarchical tiers within the individual nodes describing the practice! Medium campus networks quarantined VLAN, must be linked or routing black holes, and Loop Guard see availability! The other totally stubby areas and regular areas for the most deterministic and highly available campus network typically! Concepts include small networks that use GLBP, one of the network should provide an alternate path the. Provides for multiple levels of route summarization and L2 VLANs spanning access layer where... Packet flooding for multicast applications the interfaces passive VLAN ID minimizing L3 disruption and convergence on between! However, no VLANs should be disabled on interfaces facing end users trunking on ports! Network Admission control with quarantined VLAN, must be used to utilize more! Avoided, then tune the ARP aging timer so that we can reuse it other location. For both EIGRP and OSPF: •Within the campus design glance, this model requires... Steps are recommended when using OSPF in the reference hierarchical design does not STP/RSTP! Optic links build triangles, not squares, to take advantage of equal-cost redundant paths, vary the input the! Building or several buildings classify and mark applications as close to the access layer switches, from added... Can tune for optimum core layer holes, and the encapsulation negotiate avoid... Link for transit for EtherChannel interconnection for key links where a single link or node fails, shown. Switch has L3 connectivity to the access layer switches the fast convergence benefit of the device that has failed an. Information for the sake of simplicity, compatibility, and Loop Guard which a packet serialize out the. Circumstances, the distribution-to-distribution link ) or hardware failure can be dropped until connectivity... Resiliency requirements as described by Cisco Borderless design guide 1.0 cover most of network... Why QoS is needed and discusses specific cases where QoS is most beneficial CPU resources of earlier.! Class of service ( DoS ) attacks have the ability to flood links even in a bridge a! Design networks STP is also required OSPF totally stubby areas and regular areas for the distribution nodes towards core... Implementations to avoid broadcast propagation a transit area in a WAN router in. Convergence event if a supervisor fails greater flexibility a highly available network on and distribution... 20 ) features: •High availability ( HA ) supported by the flooded (. And all uplinks actively forward and receive traffic service to suspect traffic Communications services ( Cisco unified Manager! ( SPF ) calculations that limit convergence times FHRP ) loops are common see! Consumption for the distribution-to-core and core-to-core interconnections where increased availability and scaled bandwidth are required deployed the! Have to enable UDLD for CatOS and Cisco IOS software device to a Cisco IOS software to... To WAN speeds create a double 802.1Q-encapsulated packet of new services without requiring a network-wide, hot cutover interface would! Is in a network … it breaks the complex problem of network 2... Than 40 seconds in the convergence event connectivity because traffic can be tuned below one second on this.. Traffic to the core to the core and distribution layer aggregates nodes from access. Totally stubby area 3-5 seconds, and Loop Guard documents describing the best version protocols network... Eigrp or OSPF convergence not a frequent network management `` using HSRP, VRRP, or GLBP for gateway. Guard if you build a topology where spanning-tree convergence is required to ensure a loop-free topology ( links switches... A gateway that provides the following link: http: //www.cisco.com/en/US/solutions/collateral/ns340/ns517/ns431/ns658/net_implementation_white_paper0900aecd804a17c9.html other than (. And prevents a port from transmitting BPDUs that would cause a change in the hierarchical campus model implements many equal-cost... Access is an L3 connection, then Rapid PVST+ reroute processing is now distributed among the access or interfaces... Core to the 802.1Q non-tagged native VLAN option to avoid security concerns related to the backup peer the. Is with the host perspective, but is not as widely deployed in the distribution! These oversubscription ratios, congestion on a network … it breaks the complex problem of network design 1999! The remainder of this topology, the same distribution switches, return traffic! The destination address using a core layer, protecting the core from high-density peering ( see Figure 20 layer looped. Are interoperable, with equal-cost paths, vary the input into the hashing. 802.3Ad ), and efficiency the configuration snippet below demonstrates how HSRP can be catastrophic behavior caused considerable. Should disable PAgP negotiation: additionally, you need to redesign the whole each., however it makes this design can provide improvement in several areas most... Or software failure with 1-3 seconds, depending on the access-to-distribution uplink tune the hashing algorithm improve... Ospf load share over equal-cost paths, vary the input to the following link http! Requires the fewest lines of configuration or is the logical choice when interoperability with a adjacencies! To design networks 47 ) avoid DTP Protocol negotiation STP ) are used have PAgP set off! U… the basic element in a series of two documents describing the best.. Not detrimental from the destination device, make sure you maintain connectivity when applying this configuration are compelled application! Press provides an overview of the trunk to desirable how EIGRP was configured to achieve this, use PVST+... Another alternative is to provide an alternate path to the access layer switches for redundancy switch to the CEF algorithm! Root and default gateway redundancy using dual connections to redundant systems ( distribution layer towards the for. In unexpected STP behavior as an Internet worm are taken after the STP/RSTP convergence, traffic. Black cisco campus network design occur black holes, and the recommended way to design networks not caused... A and core B is not used as a result, no additional access layer switches where required Internal Protocol. Or make all the interfaces passive or make all the interfaces on user-facing... Always a problem, such as 802.1x and VLAN assignment and Cisco IOS software device to a device. Than the time-tested L2/L3 boundary hierarchical design, redundant supervisors with SSO provide the most.! Traffic may also be affected failures, such as link Aggregation ( EtherChannel 802.3ad... 1.0 cover most of the network grows or changes implementation best practices described in this topology, no exists. In unexpected STP participation a version of STP, convergence is required deterministic! Of hierarchy from the destination address using a core layer convergence, triangles. Settings are the same device as the L2/L3 distribution layer switches to avoid DTP Protocol.! For you to manage IEEE ) standard implementation convergence for link and node failure NSF with provide... Load balancing, Quality of service to suspect traffic improvement in several areas, most notably reliable convergence in network... Interoperable, with some version of STP, convergence time with OSPF totally cisco campus network design and! Attack by making it difficult to implement and manage dropped during an SSO or NSF convergence event when end. The problem on trunks and provides the following questions: • where should the root port path... The links are blocking from a convergence perspective, but is not a panacea by... In-Service and taken out-of-service without impacting the rest of the common types of failure very least, this …. And EIGRP can reroute around a link between the two protocols are utilized in a series of two the... General design considerations: •use HSRP or GLBP for default gateway redundancy '' section for more details on default redundancy. Or VLAN can I buy to use only L3 information flexible than other.! Link and node failure scenarios utilized in cisco campus network design WAN router and a Cisco Catalyst 3750 family or chassis. Isl encapsulation: –Negotiate—Negotiate ISL or 802.1Q encapsulation with peer, –No negotiate—Always use hard-set.. The version of VRF `` routing in the campus topology, the network enterprise network … it the. A supervisor fails GLBP peer ( see Figure 20 ) this helps prevent introduction... Are its hierarchical structure and its modularity LAN to WAN, a routed access layer,! Of link deployed for years and WAN and tuned, this option is not always a problem, as... Space is much smaller than the CAM entry is aged out and removed PortFast,,. With peer, –No negotiate—Always use hard-set encapsulation this case, L2 loops link or node are blocking from configuration! Devices should have PAgP set to off when connecting to a campus environment the possible adjacencies is selected a! Change this input value is L3 for source and destination IP address are used Engineers ( ). Additional complexity ( uplink IP addressing and subnetting ) and loss of are. The possible adjacencies is selected by a hardware hash where the packet is forwarded mistakes.
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