Switch Meshing Paper Tech Brief

8/2/2019 Switch Meshing Paper Tech Brief

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ProCurve Networking

LAN Aggregation ThroughSwitch Meshing

Technical White paper


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Introduction ............................................................................................................... 3Understanding Switch Meshing...................................................................................... 3

Creating Meshing Domains ........................................................................................5Types of Meshing Domains ........................................................................................ 6Meshed and Non-meshed Ports .................................................................................. 8Different Speeds for Links ......................................................................................... 8Easy Configuration ................................................................................................... 8Connecting Multiple Meshing Domains ......................................................................... 8

Preventing Broadcast Storms ........................................................................................ 9Locating Unknown Destinations ..................................................................................... 9Using STP with Switch Meshing ................................................................................... 10802.1Q VLANs and Meshed Switches............................................................................ 11Additional Guidelines for Meshing Domains ................................................................... 11

Enabling Protocols in the Meshing Domain ................................................................. 12Backward Compatibility with Older Switches............................................................... 12

Conclusion ............................................................................................................... 12Glossary of Terms ..................................................................................................... 13


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Introduction

Because companies rely on their network to perform critical business tasks, that network mustbe fast, and it must be reliable. However, companies do not have an unlimited IT budget; theycannot add an infinite number of switches and high-speed cables to keep pace with usersdemand for bandwidth and to eliminate a single point of failure on the network.

ProCurve Networking offers a LAN aggregation technology that helps companies as diverse asthe Denver Regional Transportation District; GMA Network, Inc.; and Venetian Resort-Hotel-Casino maximize their investment in switches and cabling. Called switch meshing, this

technology:

Provides significantly better bandwidth utilization than either Spanning Tree Protocol (STP) orstandard port trunking (which is also called port aggregation)

Improves network performance by reducing congestion and load balancing traffic Eliminates a single point of failure Provides quick failover if a switch or link becomes unavailable Is easy to set up Supports flexible configurationsProCurve Networking has patented this unique technology, which is available on the ProCurveSwitch 3400cl, 5300xl, and 6400cl Series as well as on older ProCurve switches: 1600M, 2400M2424M, 4000M, and 8000M. (The older switches have some limitations, which are explained

later in this white paper.)

This white paper provides an overview of switch meshing and describes how you can configureit for different types of network environments.

Understanding Switch Meshing

In switch meshing, multiple switches are redundantly linked together to form a meshing domain(see Figure 1). Like STP, switch meshing eliminates network loops by detecting redundant linksand identifying the best path for traffic. When the meshing domain is established, the switchesin that domain use the meshing protocol to gather information about the available paths and todetermine the best path between switches. To select the best path, the meshed switches usethe following criteria:

Outbound queue depth, or the current outbound load factor, for any given outbound port in apossible path

Port speed, based on factors such as 10 Mbps, 100 Mbps, 1000 Mbps (or 1 Gbps), 10 Gbps,full-duplex, or half-duplex

Inbound queue depth for any destination switch in a possible path Increased packet drops, indicating an overloaded port or switchIn Figure 1, for example, the workstations attached to Switch 3 need to access the serversattached to Switch 2. Based on the meshing criteria, the switches in this meshing domainidentify the best path as follows: they transmit the data from Switch 3 to Switch 1, whichforwards it to Switch 2. Switch 2, in turn, sends the data to its destinationone of the servers.


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Figure 1. Identifying the Best Paths Through a Meshing Domain

Unlike STP, however, switch meshing does not permanently block the unused path between twoswitches. Within a meshing domain, all the paths between switches remain open, and switchescan distribute traffic across these available paths as needed to maintain the same latency frompath to path.

Most of the criteria used to identify the best path are based on network conditions. Theoutbound queue depth, inbound queue depth, and packet drops all indicate which switches andports are handling the most traffic. As you would expect, the values for these criteria changeover time. To load balance traffic, the meshed switches periodically check this information,identify the best paths based on current network conditions, and then communicate thisinformation to all the other switches in the meshing domain.

The switches use the current path information to assign paths on a per-connection basis. Whena new connection is established between a source address and a destination address, the trafficbetween the pair stays on the assigned path until the connection ages out or the pathexperiences a break. When the two devices later send new traffic, the switches use the bestpath at that time. Because network conditions may have changed, the best path may not be thesame. For example, due to an increase in traffic, the meshed switches may detect packet dropsbecause a port is overloaded. In this case, the switches will send the new traffic through adifferent path than was used previously.

In the meshing domain shown in Figure 1, for example, the links between Switches 1 and 2

handle a high volume of traffic and occasionally become saturated. When a workstationattached to Switch 3 sends data to a server attached to Switch 2, Switch 3 sends the data toSwitch 4, rather than to Switch 1. Switch 4 then sends the data to Switch 2 for delivery to itsfinal destination (see Figure 2).


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Which switches and links provide services for the entire company? For example, if an edgeswitch went down, that failure would affect a group of users. However, if a core switch wentdown, that failure would affect the entire company. Although both failures would reduce yourcompanys productivity, losing network services for the entire company would obviously bemore costly than losing network services for a group of users.

Which switches and links deliver mission-critical services to the company? For example, ifyour company is a call center, the software program that representatives use to gatherinformation about customers is critical to the operation of the company and must be availableat all times.

During your evaluation, you may want to perform some simple tests during peak operations todetermine latency on different links. You can use the p i ng command to determine the latencybetween two endpoints. When you send a p i ng to a remote device, the results show theroundtrip time in milliseconds, which will give you a basic idea of the latency when traffic istransmitted between two devices.

Types o f Mesh ing Dom a ins

After you identify the areas that need additional bandwidth or redundant links, you candetermine which type of meshing domain you need to implement. There are two types ofmeshing domains:

Fully connected meshing domain Partially connected meshing domainIn a fully connected meshing domain, every switch is directly connected to every other switch inthe domain (see Figure 3). This type of meshing domain provides the highest degree ofavailability because it eliminates every single point of failure between the switches. You canconfigure multiple meshed ports between each switch to provide higher bandwidth.

Figure 3. Fully Connected Meshing Domain


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You may want to implement a fully connected meshing domain for core network switches thatprovide connectivity to critical services such as applications, the Internet, or email. Then, if onelink goes down, users can still access the services they need to perform their jobs.

In a partially connected meshing domain, only some switches are directly connected to otherswitches. For example, in Figure 4, a meshed backbone connects Switches 1 and 2. Switches 3,4, 5, 6, 7, and 8 are connected to switches 1 and 2. However, Switches 3, 4, 5, 6, 7, and 8 arenot directly connected to each other.

You may want to implement a partially connected meshing domain if it includes both core andedge switches and it is not vital that the edge switches be directly connected to each other.

Figure 4. Partially Connected Meshing Domain

The type of meshing domain that you implement determines the number of switches allowed inthe domain. If you establish a fully connected meshing domain, the domain can contain amaximum of five switches. A partially connected meshing domain, on the other hand, caninclude a maximum of 12 switches. For best performance, however, ProCurve Networkingrecommends that a partially connected meshing domain contain eight switches.

The shortest path between any two nodes in the meshing domain can include no more than fivehops. A path of six or more meshed hops between two nodes is unusable. In most meshingtopologies, however, a shorter path is normally available, so switches will use paths of five hopsor fewer through the meshing domain.


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Meshed and Non-m eshed Por t s

A meshed switch can have some ports in the meshing domain and some ports outside themeshing domain. You enable meshing for point-to-point links between two switches that arepart of a meshing domain. You do not enable meshing for ports that connect to:

Devices such as workstations, servers, or printers Switches that are outside the meshing domain HubsIf all the ports on a switch are enabled for meshing, the switch is called a meshed core switch.If some ports are meshed and others are not, the switch is called a meshed edge switch. (Thesedesignations refer to the switchs role in the meshing domain, not its role in the network itself.)Most switches in a meshing domain will be meshed edge switches.

You can enable up to 24 meshed ports on a switch, and all of the meshed ports on a givenswitch belong to the same meshing domain.

If a switch port is not configured for meshing, you should not connect it to a meshed port onanother switch. If you connect a meshed port to a non-meshed port, the meshed port will shutdown. For this reason, meshing domains do not allow the following:

Hub links between meshed switch links Switches that are not configured for switch meshingDi f fe ren t Speeds fo r L inksUnlike trunked (or aggregated) ports, redundant links in a meshing domain can be of differenttypes and speeds. You can connect two switches with any combination of 10 Mbps, 100 Mbps,1 Gbps, or 10 Gbps ports. For example, you might connect two switches through a 100 Mbpsport and a 1 Gbps port. This flexibility enables you to use your companys existing cables andswitch capabilities.

Easy Conf igur a t io n

When your company receives additional budget to upgrade cabling or add switches to itsnetwork, switch meshing makes it easy to make these changes. Configuring switch meshing is asimple process: you use the m e s h command to add ports to the meshing domain. Likewise, youcan use the n o m e sh command to remove ports from the meshing domain. After adding orremoving a meshed port on a switch, you must reboot the switch for changes to take effect.

You can avoid repeated system disruptions by configuring switch meshing on all ports beforeyou implement the meshing domain. If a meshed port detects a non-meshed port on theopposite end of a point-to-point connection, the link is blocked. As you bring up switch meshingon various switches, some meshed ports may be blocked temporarily. These conditions shouldclear themselves after you configure all the switches for meshing and then reboot them. Toreduce the effect of blocked ports while the meshing domain is established, you can configuremeshing either before installing the meshed switches in the network or before connecting thecables between the meshed ports.

Connec t ing Mu l t i p le Mesh ing Dom a ins

Depending on your network, you may want to create multiple meshing domains. For example,you may want to create a meshing domain that encompasses the core switches on the network.You may also want to create a separate meshing domain for the edge switches that provide

connectivity for departments such as customer service and accounting.

To connect two or more meshing domains, you can use either a non-meshed switch or a non-meshed link. In Figure 5, for example, a non-meshed link connects two switches in two differentmeshing domains. The ports that connect these two meshing domains are not enabled formeshing.


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Figure 5. Connecting Multiple Meshing Domains

Preventing Broadcast Storms

Although unicast traffic can be routed across alternate paths in a meshing domain, broadcast

and multicast traffic must be handled differently. To prevent broadcast or multicast storms,each switch in a meshing domain should receive only one copy of a broadcast or multicastpacket. When the meshing domain is established, each switch identifies a broadcast path.(Broadcast and multicast traffic entering the meshing domain from different edge switches willprobably take different paths.) Unless a link or a switch fails, the meshed switch will maintainthis broadcast path.

When a meshed edge switch receives a broadcast through a non-meshed port, it floods thebroadcast out all its other non-meshed ports. However, it sends the broadcast out only themeshed ports that are part of the broadcast path. As a result, only one copy of the broadcastreaches the other meshed edge switches for broadcast out their non-meshed ports.

Meshed core switches send the broadcast only through ports (or paths) that link to separatemeshed edge switches. That is, meshed core switches send the broadcast only on thebroadcast path.

Handling broadcast and multicast traffic in this way helps keep the latency for these packets toeach switch as low as possible.

Locating Unknown Destinations

Within a meshing domain, switches exchange address information from their switch addresstables, so that they can transmit packets across the best path to their ultimate destination. If aswitch receives a unicast packet with an unknown destination, that switch does not broadcastthe packet across the meshing domain. To learn the destination for the unicast packet, theswitch sends a query to all the switches in the meshing domain. These switches then send802.2 test packets through their non-meshed ports. After learning the destination for theunicast packet, meshed switches can forward subsequent packets with the same destinationaddress.

To reduce the number of unknown destination packets, you can configure the switches to retaindevice addresses for longer periods. For IP networks, you can also speed up the discoveryprocess by assigning switches an IP address.


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Using STP with Switch Meshing

Although switch meshing provides distinct advantages over STP, you may still want to run STPon your companys network. For example, you might enable STP to eliminate redundant loopsoutside the meshing domain. You might also enable STP if you use one meshed link and onenon-meshed link to connect two switches.

You can use switch meshing in conjunction with STP. Within the meshing domain, the switchmeshing protocol identifies redundant links and the best paths for trafficwith the addedbenefit of using redundant links as needed to load balance traffic (see Figure 6).

Outside the meshing domain, STP manages redundant links. STP interprets the meshing domainas a single link and manages any redundant links that are established through non-meshedports on meshed edge switches

Figure 6. Using STP with Switch Meshing


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In Figure 6, STP may temporarily block a meshed link because STP interprets the cost on anexternal trunked link to be less than the cost on a meshed link. If this condition occurs, themeshed switch with the blocked link will automatically increase the cost on the external (non-meshed) link so that STP will block the external link and unblock the meshed link. This processtypically resolves itself in approximately 30 seconds.

If you use STP with a meshing domain, all the switches in the domain should run the sameversion of STPone of the following:

STP (802.1D) RSTP (802.1w) MSTP (802.1s)If the meshing domain includes a ProCurve Switch 1600M, 2400M, 2424M, 4000M, or 8000M,you must use STP (802.1D) because these switches do not support other versions of STP.

802.1Q VLANs and Meshed Switches

If your companys network includes virtual LANs (VLANs) and you want to use STP, you maywant to use either Per VLAN Spanning Tree (PVST) or MSTP (802.1s). If you configure PVST andMSTP correctly, you can better utilize your existing network bandwidth because these protocolscan establish different network paths for different VLANs. For example, VLAN 10 may use adifferent root bridge and network links than VLAN 11 does. However, because you must run

multiple instances of Spanning Tree, configuring and troubleshooting such an environment canbe complicated.

In contrast, configuring switch meshing for a multi-VLAN environment is simple: you configureall the static VLANs on each meshed switch (even if no ports on the switch are assigned to aparticular VLAN). When you enable switch meshing for a port, that port automatically becomesa member of all the static VLANs created on the switch. Because all meshed ports are membersof all VLANs, they can forward traffic for any VLAN.

If you want non-meshed ports on a meshed edge switch to handle certain VLAN traffic, youmust manually assign those ports to the VLAN. If a non-meshed port is not a member of aparticular VLAN, it cannot forward traffic originating in that VLAN to non-meshed devices.Likewise, the connecting port on the non-meshed switch must belong to the same VLAN, or itcannot receive the traffic. (It is necessary to use a router to communicate between VLANs.)

If you have configured VLANs on your companys network, you may also be using GARP VLANRegistration Protocol (GVRP), which supports the creation of dynamic VLANs. A switch port thatruns GVRP advertises the static VLANs for which it has been configured. Other GVRP ports canthen join those VLANs as necessary for extending the VLANs throughout the network.

If one switch in the meshing domain runs GVRP, then all switches in the domain must run it.Otherwise, the meshed switches cannot forward dynamic VLAN traffic. If GVRP is enabled,meshed ports join dynamic VLANs in the same way that non-meshed ports join dynamic VLANs.(The ProCurve 1600M, 2400M, 2424M, 4000M, and 8000M switches do not support GVRP. If ameshing domain includes any of these switches, you must disable GVRP on all switches in thedomain.)

Additional Guidelines for Meshing Domains

All switches in the meshing domain must support ProCurve Networkings switch-meshingprotocol. In addition, all meshed switches from the same product family must run the sameswitch software version. For example, if you update the software version on one ProCurve5300xl Series switch, you must update the software version on any other ProCurve 5300xlSeries switch in the meshing domain. (Whether or not you implement switch meshing, ProCurveNetworking recommends that you always use the most recent software version available for theswitches in your companys network.)

When you enable meshing by assigning ports to a meshing domain, you must disable theswitchs routing features (IP routing, Routing Information Protocol [RIP], and Open ShortestPath First [OSPF]). The switch-meshing protocol handles routing functions for the switch. If youare using the ProCurve Switch 3400cl or 6400cl Series in a meshing domain, you must alsodisable stacking on the switch. Stacking is not supported with switch meshing. (Stackingenables a group of up to 16 switches to share a single IP address and broadcast domain.)


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Enab l ing Pro toco ls in t he Mesh ing Dom a in

When configuring a meshing domain, you should ensure that the switches in the domain areconfigured in the same way. For example, you should make a list of the protocols running oneach switch in the domain because the switches in the meshing domain must be configured inthe same way. As mentioned earlier, if you enable GVRP on one switch in the meshing domain,you must enable GVRP on the other switches in the meshing domain.

In addition, Internet Group Management Protocol (IGMP), or IP multicast, must run on all ornone of the switches in a meshing domain. Like trunked ports, the meshing domain appears asa single port to IGMP. With meshing domains, however, IGMP and multicast traffic can be sent

over several links in the domain in the same manner as broadcast packets.

This same rule applies to Link Layer Discovery Protocol (LLDP). If one switch in the meshingdomain is running LLDP, all the switches in the domain must run the same protocol.

B ackw ard Com pa t i b i l it y w i t h Olde r Sw i t ches

As mentioned earlier, if your company has older ProCurve switches (such as the 1600M, 2400M,2424M, 4000M, or 8000M), you can use these switches in the same meshing domain thatincludes ProCurve Switches 3400cl, 5300xl, and 6400cl Series. When creating a meshingdomain that includes the older switches, however, you must configure the ProCurve Switches3400cl, 5300xl, and 6400cl Series to use the mesh backward compatibility mode.

In addition, the older switches do not allow different switches to use the same media accesscontrol (MAC) addresses to connect to a host, even when the connections are through different

VLANs. If the meshing domain includes multiple switches that use the same MAC addresses, youcannot add an older switch to the meshing domain. Likewise, you cannot merge a meshingdomain that includes duplicate MAC addresses with a meshing domain that includes anolder switch.

Conclusion

With switch meshing, your company can make every switch, every port, and every cable count.You can provide high availability while improving network performance. Although STP providesfailover capabilities, it does not improve network performance. Instead, redundant links remainidle even when active links become saturated. With switch meshing, on the other hand,switches can use redundant links to offload traffic from overused ports and saturated links,speeding up the transfer of data across the network.

Keeping redundant links open has an additional benefit: failovers are quick. If a switch or a linkbecomes unavailable, switch meshing can rapidly reroute traffic.

In addition, switch meshing is easy to configureeven for multi-VLAN environments. Andbecause switch meshing supports flexible configurations, you can use the capabilities of yourexisting switches. You can connect the switches in a meshing domain through any combinationof port and cable speeds.


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Glossary of Terms

GVRPGARP VLAN Registration Protocol is an application of the Generic Attribute RegistrationProtocol (GARP). GVRP enables a switch to dynamically create 802.1Q-compliant VLANs on linksthat are connected to other devices running GVRP.

Mesh i ng dom a i nA group of meshed switch ports that exchange meshing protocol packets.Paths between these ports can have multiple redundant links without creating broadcast storms

Meshed edge sw i t chA switch that has some ports configured for switch meshing (and

therefore in the switch meshing domain) and some ports not configured for switch meshing(and therefore outside the domain).

Meshed core sw i t ch A switch that has all ports configured for switch meshing.

Meshed por t A port that is configured to exchange meshing protocol packets.

Non-m eshed po r t A port that is not configured to exchange meshing protocol packets.

VLANsA Virtual LAN (VLAN) is comprised of multiple ports operating as members of the samesubnet (broadcast domain). Ports on multiple devices can belong to the same VLAN, and trafficmoving between ports in the same VLAN is bridged (or switched).

A static VLAN is an 802.1Q-compliant VLAN configured with one or more ports that remainmembers, regardless of traffic usage. A dynamic VLAN is an 802.1Q-compliant VLANmembership that the switch temporarily creates on a port to provide a link to another port in

the same VLAN on another device.


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2005 Hewlett-Packard Development Company, L.P. The information containedherein is subject to change without notice. The only warranties for HP products andservices are set forth in the express warranty statements accompanying suchproducts and services. Nothing herein should be construed as constituting anadditional warranty. HP shall not be liable for technical or editorial errors oromissions contained herein.

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