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Switch Features Explained

19

RSTP allows you to implement alternative paths for network traffic in the
event of path failure and uses a loop-detection process to:

■

Discover the efficiency of each path.

■

Enable the most efficient path.

■

Disable the less efficient paths.

■

Enable one of the less efficient paths if the most efficient path fails.

RSTP is an enhanced version of STP (Spanning Tree Protocol) and is fully
compatible with STP systems. RSTP can restore a network connection
quicker than the legacy STP feature. RSTP can detect if it is connected to a
legacy device that only supports IEEE 802.1D STP and will automatically
downgrade to STP on that particular port.

RSTP conforms to the IEEE Std 802.1w-2001.

For more information about RSTP, see

Chapter 4 “Using Resilience

Features”

.

Switch Database

The Switch Database is an integral part of the Switch and is used by the
Switch to determine if a packet should be forwarded, and which port
should transmit the packet if it is to be forwarded.

For more information about the Switch Database, see

Chapter 5 “Using

the Switch Database”

.

Traffic Prioritization

The traffic prioritization capabilities of your Switch provides Class of
Service (CoS) prioritization to your network. You can prioritize traffic on
your network to ensure that high priority data is transmitted with
minimum delay.

For more information about traffic prioritization, see

Chapter 6 “Using

Traffic Management”

.

Rate Limiting

Rate limiting is the restriction of the bandwidth to or from a section of
your network. Limiting the rate of network traffic reduces the stress on
your network and, when used with traffic prioritization, ensures that
important traffic is not held up when the network is busy.

For more information about rate limiting, see

Chapter 6 “Using Traffic

Management”

.

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Содержание SuperStack 3 3812

Страница 1: ...http www 3com com Part No DUA1740 0BAA02 Published September 2004 SuperStack 3 Switch 3812 Switch 3824 and Switch 3848 Implementation Guide 3C17401 3C17400 3CR17402 91...

Страница 2: ...ned in or delivered to you in conjunction with this User Guide Unless otherwise indicated 3Com registered trademarks are registered in the United States and may or may not be registered in other count...

Страница 3: ...guration Save and Restore 17 Multicast Filtering 18 Rapid Spanning Tree Protocol 18 Switch Database 19 Traffic Prioritization 19 Rate Limiting 19 RMON 20 Broadcast Storm Control 20 VLANs 20 Automatic...

Страница 4: ...st 37 Electing the Querier 37 Host Messages 37 Response to Queries 37 Role of IGMP in IP Multicast Filtering 38 4 USING RESILIENCE FEATURES Rapid Spanning Tree Protocol 40 Rapid Spanning Tree Protocol...

Страница 5: ...RMON 59 What is RMON 59 The RMON Groups 60 Benefits of RMON 61 RMON and the Switch 61 Alarm Events 62 8 SETTING UP VIRTUAL LANS What are VLANs 63 Benefits of VLANs 64 VLANs and Your Switch 65 The Def...

Страница 6: ...t Considerations 80 What is Switch Management Login 81 Benefits of RADIUS Authentication 82 How RADIUS Authentication Works 82 Important Considerations 83 What is RADIUS 83 A CONFIGURATION RULES Confi...

Страница 7: ...GLOSSARY INDEX...

Страница 8: ......

Страница 9: ...tended for the system or network administrator who is responsible for configuring using and managing the Switches It assumes a working knowledge of local area network LAN operations and familiarity wi...

Страница 10: ...10 ABOUT THIS GUIDE Most user guides and release notes are available in Adobe Acrobat Reader Portable Document Format PDF or HTML on the 3Com World Wide Web site http www 3com com...

Страница 11: ...e To change your password use the following syntax system password password In this example you must supply a password for password Commands The word command means that you must enter the command exac...

Страница 12: ...ation about the Web interface and Command Line Interface that enable you to manage your Switch It is supplied in HTML format on the CD ROM that accompanies your Switch SuperStack 3 Switch 3812 Switch...

Страница 13: ...information when contacting us Document title Document part number on the title page Page number if appropriate Example SuperStack 3 Switch 3812 Switch 3824 and Switch 3848 Implementation Guide Part n...

Страница 14: ...14 ABOUT THIS GUIDE...

Страница 15: ...at on the CD ROM that accompanies your Switch What is Management Software Your Switch can operate in its default state However to make full use of the features offered by the Switch and to change and...

Страница 16: ...re information about aggregated links see Chapter 2 Optimizing Bandwidth Auto negotiation Auto negotiation allows ports to auto negotiate port speed duplex mode only at 10 Mbps and 100 Mbps and flow c...

Страница 17: ...mmends the Switch unit is reset to its factory default settings before you restore a configuration onto it You can reset the Switch using the system control initialize CLI command or the System Contro...

Страница 18: ...re established when the restore operation has been completed For detailed descriptions of the Configuration Save and Restore Web interface operations and Command Line Interface CLI commands please ref...

Страница 19: ...ase The Switch Database is an integral part of the Switch and is used by the Switch to determine if a packet should be forwarded and which port should transmit the packet if it is to be forwarded For...

Страница 20: ...is blocked until the broadcast traffic level drops below the threshold This system prevents the overwhelming broadcast traffic that can result from network equipment which is faulty or configured inco...

Страница 21: ...dresses on the port are made permanent Any packets containing a source address not learnt on the port will be dropped Automatic Learning You can limit the number of addresses that can be learned on in...

Страница 22: ...22 CHAPTER 1 SWITCH FEATURES OVERVIEW...

Страница 23: ...anagement Interface Reference Guide supplied in HTML format on the CD ROM that accompanies your Switch Port Features The default state for all the features detailed below provides the best configurati...

Страница 24: ...operating in full duplex mode and Intelligent Flow Management IFM for ports operating in half duplex mode Auto negotiation Auto negotiation allows ports to automatically determine the best port speed...

Страница 25: ...rts An aggregation can be created by using two 10 100 1000 ports two SFP ports or one SFP port and one 10 100 1000 port Figure 1 shows two Switches connected using an aggregated link containing two me...

Страница 26: ...ons are extremely resilient and fault tolerant Figure 2 Dynamic Reassignment of Traffic Flows The key benefits of 802 3ad link aggregation are Automatic configuration Network management does not need...

Страница 27: ...the cost assigned for an aggregated link running at that speed As required by the IEEE Std 802 3 2002 incorporating 802 3ad no changes in cost are made according to the number of member links in the...

Страница 28: ...an aggregated link between two devices the ports in the aggregated link must not be physically connected together until the aggregated link has been correctly configured at both ends of the link Fail...

Страница 29: ...n Figure 3 illustrates a 2 Gbps aggregated link between two Switch units that is each port is operating at 1000 Mbps full duplex Figure 3 A 2 Gbps aggregated link between two Switch units To manually...

Страница 30: ...drop the traffic Implementing Jumbo Frames Jumbo frames are usually implemented on a network so that endstations that support jumbo frames can communicate with other similar devices Typically the end...

Страница 31: ...the jumbo frames support for this switch 3 Configure the servers connected to the switch to use jumbo frames to communicate with each other CAUTION The servers must be configured to only use jumbo fra...

Страница 32: ...32 CHAPTER 2 OPTIMIZING BANDWIDTH...

Страница 33: ...A multicast is a packet that is intended for one to many and many to many communication Users explicitly request to participate in the communication by joining an endstation to a specific multicast g...

Страница 34: ...ce QoS There are situations where a multicast approach is more logical and efficient than a unicast approach Application examples include distance learning transmitting stock quotes to brokers and col...

Страница 35: ...tch to forward multicast packets only to the appropriate ports The Switch snoops on exchanges between endstations and an IGMP device typically a router to find out the ports that wish to join a multic...

Страница 36: ...cast learning enabled the Switch learns that the port is to forward traffic for the multicast group and then forwards the packet to the router 4 When the router receives the report packet it registers...

Страница 37: ...s The querier normally sends messages called IGMP Host Membership Query Messages or queries every 125 seconds All the hosts hear the query because it is addressed to 224 0 0 1 the all systems on this...

Страница 38: ...ether that host is the last group member on the subnetwork by issuing a group specific query Leave group messages lower leave latency that is the time between when the last group member on a given sub...

Страница 39: ...ree Protocol RSTP The protocol configures itself automatically based on the surrounding network and is compatible with switches that use either the Spanning Tree Protocol STP or RSTP For detailed desc...

Страница 40: ...ecification To explain RSTP more effectively your Switch will be referred to as a bridge Rapid Spanning Tree Protocol RSTP The Rapid Spanning Tree RSTP is an enhanced Spanning Tree feature RSTP implem...

Страница 41: ...ality as STP For details on how the two systems differ see How RSTP Differs to STP on page 45 As an example Figure 6 shows a network containing three LAN segments separated by three bridges With this...

Страница 42: ...B STP determines which is the most efficient path between each bridged segment and a specifically assigned reference point on the network Once the most efficient path has been determined all other pa...

Страница 43: ...your Switch is 32768 Each port to have a cost This specifies the efficiency of each link usually determined by the bandwidth of the link the higher the cost the less efficient the link Table 3 shows t...

Страница 44: ...arameters each bridge is configured to forward traffic only between its Root Port and the Designated Bridge Ports for the respective network segments All other ports are blocked which means that they...

Страница 45: ...out having to wait to ensure all other bridges in the network have had time to react to the change So the main benefit of RSTP is that the configuration decision is made locally rather than network wi...

Страница 46: ...osts 300 Y to B 200 B to A 100 Port 2 on Bridge C is therefore selected as the Designated Bridge Port for LAN Segment 3 STP Configurations Figure 10 shows three possible STP configurations using Super...

Страница 47: ...How STP Works 47 Figure 10 STP configurations 1 2 3 10Mbps Hub Block Block Block Block Switch Switch Switch Switch Switch...

Страница 48: ...ically blocked because the other Switch to Switch connections have a path cost of 36 18 18 This means that both VLANs are now subdivided VLAN 1 on Switch units A and B cannot communicate with VLAN 1 o...

Страница 49: ...ease refer to Chapter 1 of the Getting Started Guide that accompanies your Switch For detailed descriptions of the Web interface operations and the Command Line Interface CLI commands that you require...

Страница 50: ...on is removed from the network its entry is also removed from the database Learned entries are removed from the Switch Database if the Switch is reset or powered down Non aging learned If the aging ti...

Страница 51: ...ic Prioritization Traffic prioritization allows high priority data such as time sensitive and system critical data to be transferred smoothly and with minimal delay over a network Traffic prioritizati...

Страница 52: ...o the appropriate queue depending on its priority level for onward transmission across the network The Switch determines which queue to service next according to the queuing mechanism selected see Tra...

Страница 53: ...where else in the network and not in the Switch itself Note also that 802 1D service levels are fixed and cannot be altered 3 Create Profiles The next step is to create a profile which associates clas...

Страница 54: ...n a header field immediately following the destination MAC address and Source MAC address 802 1D Priority Levels The traffic prioritization feature supported by the Switch at layer 2 is compatible wit...

Страница 55: ...raffic so that different levels of service can be applied to it on a network DiffServ is a layer 3 function and the service to be applied is contained within the DSCP field which is in the IP header o...

Страница 56: ...t the IP port number then the packet will be sent out with the default priority Traffic Queues It is the multiple traffic queues within the Switch hardware that allow packet prioritization to occur Hi...

Страница 57: ...at which a port can receive or send traffic can be used to ease congestion on bottlenecks in your network and provide simple prioritization when the network is busy Rate limiting is commonly used in t...

Страница 58: ...te leaving the Switch is limited rather than the traffic arriving at the Switch This ensures that the traffic is prioritized before rate limiting is applied and the lowest priority packets are dropped...

Страница 59: ...ve your network efficiency and reduce the load on your network This section explains more about RMON It covers the following topics What is RMON Benefits of RMON RMON and the Switch What is RMON RMON...

Страница 60: ...ing parameters of your network Alarms The Alarms group provides a mechanism for setting thresholds and sampling intervals to generate events on any RMON variable Alarms are used to inform you of netwo...

Страница 61: ...polling network devices at regular intervals to gather statistics and identify problems or trends As network sizes and traffic levels grow this approach places a strain on the management workstation...

Страница 62: ...re information about the alarms setup on the Switch see Alarm Events on page 62 Events A new or initialized Switch has one Event session per port Table 4 RMON support supplied by the Switch RMON group...

Страница 63: ...Guide supplied in HTML format on the CD ROM that accompanies your Switch What are VLANs A VLAN is a flexible group of devices that can be located anywhere in a network but which communicate as if the...

Страница 64: ...st be updated manually With a VLAN setup if an endstation in VLAN Marketing for example is moved to a port in another part of the network and retains its original subnet membership you only need to sp...

Страница 65: ...ur Switch to be placed in Any one VLAN defined on the Switch Several VLANs at the same time using 802 1Q tagging The standard requires that you define the following information about each VLAN on your...

Страница 66: ...LANs Tagged and Untagged Membership Your Switch supports 802 1Q VLAN tagging a system that allows traffic for multiple VLANs to be carried on a single physical backbone link When setting up VLANs you...

Страница 67: ...ion Examples This section contains examples of VLAN configurations It describes how to set up your Switch to support simple untagged and tagged connections Using Untagged Connections The simplest VLAN...

Страница 68: ...network where the VLANs are distributed amongst more than one Switch you must use 802 1Q tagged connections so that all VLAN traffic can be passed along the links between the Switches 802 1Q tagging c...

Страница 69: ...fic is passed over the link to Switch 2 4 Configure the VLANs on Switch 2 Define VLAN 2 VLAN 1 is the default VLAN and already exists 5 Add endstation ports on Switch 2 to the VLANs Place the endstati...

Страница 70: ...h Switches The relevant ports should be listed in the VLAN members summary 8 Connect the Switches Connect port 12 on Switch 1 to port 11 on Switch 2 The VLANs are now configured and operational and th...

Страница 71: ...For detailed information on setting up your Switch for management see the Getting Started Guide that accompanies your Switch For detailed descriptions of the Web interface operations and the Command L...

Страница 72: ...before whichever of the three options for IP configuration manual auto none was last configured is activated when the Switch powers up again You can switch to manual IP configuration at any time usin...

Страница 73: ...r Support Your Switch has been tested to interoperate with DHCP servers that use the following operating systems Microsoft Windows 2000 Server Microsoft Windows NT4 Server Sun Solaris v2 5 1 If you wa...

Страница 74: ...74 CHAPTER 9 USING AUTOMATIC IP CONFIGURATION...

Страница 75: ...your switch remotely or over an insecure network the Switch can encrypt all HTTP traffic to and from the Web interface using the Secure Sockets Layer SSL of HTTP If your network traffic is intercepte...

Страница 76: ...ted If you cannot generate an X 509 certificate yourself you can buy one from one of the Certifying Authorities or your ISP Each Switch will require its own X 509 certificate Securing Access to the Co...

Страница 77: ...packet matches an access list rule when it s destination IP address falls with the values of the rule When a match is found the path the packet takes is determined by the rule and is either forwarded...

Страница 78: ...rning addresses and the port enters Learning Off mode Access to the port is then restricted to the devices that have already been learned on the port Network Login When the user has been successfully...

Страница 79: ...llows the user of a port to be identified This user identification information can be used for service accounting or billing or to help network administrators resolve problems Network Login is a featu...

Страница 80: ...it should also be configured to be a Spanning Tree Protocol STP edge port This minimizes the delay before STP places the port into the forwarding state For further information about RADIUS see What is...

Страница 81: ...nt Login If you intend to manage the Switch using the Web interface or the Command Line Interface you need to log in with a valid user name and password For further information on managing the Switch...

Страница 82: ...asswords require only a single action on the RADIUS database and are reflected immediately Your Switch is fully compliant with the industry standard RADIUS protocol For further information about RADIU...

Страница 83: ...r Telnet The user names and passwords stored in the local Switch database may not be the same as those stored on the RADIUS server When a user account is created on a RADIUS server an equivalent accou...

Страница 84: ...84 CHAPTER 10 MAKING YOUR NETWORK SECURE...

Страница 85: ...ons up to 100 m 328 ft The different types of Gigabit Ethernet media and their specifications are detailed in Table 6 Table 6 Gigabit Ethernet cabling Gigabit Ethernet Transceivers Fiber Type Modal Ba...

Страница 86: ...e 20 illustrates the key topology rules and provides examples of how they allow for large scale Fast Ethernet networks Figure 20 Fast Ethernet configuration rules The key topology rules are Maximum UT...

Страница 87: ...a repeater out to the endstations Configuration Rules with Full Duplex The Switch provides full duplex support for all its ports Full duplex allows packets to be transmitted and received simultaneous...

Страница 88: ...88 APPENDIX A CONFIGURATION RULES...

Страница 89: ...B NETWORK CONFIGURATION EXAMPLES This chapter contains the following section Simple Network Configuration Examples Desktop Switch Example...

Страница 90: ...he Switch 3812 Switch 3824 or Switch 3848 can be used in your network Desktop Switch Example The example in Figure 21 shows how a Switch 3848 and a Switch 4200 can be used for a group of users that re...

Страница 91: ...to two parts Simple Overview Gives a brief overview of what an IP address is Advanced Overview Gives a more in depth explanation of IP addresses and the way they are structured Simple Overview To oper...

Страница 92: ...ddress InterNIC Registration Services is the organization responsible for supplying registered IP addresses The following contact information is correct at time of publication World Wide Web site http...

Страница 93: ...lasses of IP addresses are as follows Class A address Uses 8 bits for the network part and 24 bits for the host part Although only a few Class A networks can be created each can contain a very large n...

Страница 94: ...a subnetwork part a subnet mask identifies the bits that constitute the subnetwork address and the bits that constitute the host address A subnet mask is a 32 bit number in the IP address format The...

Страница 95: ...The number that includes both the Class B natural network mask 255 255 and the subnet mask 255 240 is sometimes called the extended network prefix Continuing with the previous example the subnetwork...

Страница 96: ...ments When it receives the IP packets the gateway determines the next network hop on the path to the remote destination and sends the packets to that hop This could either be the remote destination or...

Страница 97: ...ging The automatic removal of dynamic entries from the Switch Database which have timed out and are no longer valid Aggregated Links Aggregated links allow a user to increase the bandwidth and resilie...

Страница 98: ...vices CA See Certificate Authority cache Stores copies of frequently accessed objects locally to users and serves them to users when requested Certificate Authority An organization that issues Digital...

Страница 99: ...packet toward its destination using a networking device Forwarding Database See Switch Database filtering The process of screening a packet for certain characteristics such as source address destinat...

Страница 100: ...ons IEEE Std 802 1D 1998 Edition A standard that defines the behavior of bridges in an Ethernet network IEEE Std 802 1p A standard that defines traffic prioritization 802 1p is now incorporated into t...

Страница 101: ...the standard for sending data through a network IP is part of the TCP IP set of protocols that describe the routing of packets to addressed devices IPX Internetwork Packet Exchange IPX is a layer 3 a...

Страница 102: ...ect to a LAN have a MAC address assigned to them as they are used to identify other devices in a network MAC addresses are 6 bytes long main port The port in a resilient link that carries data traffic...

Страница 103: ...rk repeater A simple device that regenerates LAN traffic so that the transmission distance of that signal can be extended Repeaters are used to connect two LANs of the same network type resilient link...

Страница 104: ...ocol used for encrypting network traffic It is commonly used to encrypt HTTP traffic between and browser and a Web server standby port The port in a resilient link that takes over data transmission if...

Страница 105: ...vice TFTP Trivial File Transfer Protocol Allows you to transfer files such as software upgrades from a remote device using the local management capabilities of the Switch traffic prioritization A syst...

Страница 106: ...106 GLOSSARY...

Страница 107: ...How traffic is processed to provide CoS 52 service levels 53 traffic classification 53 D default gateway 96 Default VLAN 65 Designated Bridge 44 Designated Bridge Port 44 E event notification 20 Event...

Страница 108: ...QoS apply QoS profile 53 R RADIUS 81 83 authentication 82 Rapid Spanning Tree Protocol RSTP 18 40 registered IP address obtaining 92 Remote Monitoring See RMON Restore 17 RMON 20 alarm events 62 bene...

Страница 109: ...witch management login 75 T topology rules for Fast Ethernet 86 topology rules with full duplex 87 traffic classification 802 1D 54 traffic prioritization 19 51 802 1D 54 queues 56 V VLANs 63 benefits...

Страница 110: ...110 INDEX...

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