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Assurance of loop-free networks, Ability to import non-OSPF routing information

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452 CHAPTER 19: OPEN SHORTEST PATH FIRST (OSPF) ROUTING s Support for virtual links to noncontiguous areas - As discussed earlier, OSPF can partition large autonomous systems into smaller, more manageable subdivisions, called areas. An OSPF backbone is responsible for distributing routing information between the areas of an autonomous system. This backbone itself has all the properties of an area and consists of those networks that are not contained in any area. Although the backbone must be contiguous, backbone routers can also be connected by means of a virtual link. Virtual links can be configured between any two backbone routers that have an interface to a common nonbackbone area. OSPF treats two routers that are joined by a virtual link as if they were connected by an unnumbered point-to-point network. For more information, see "Virtual Links" later in this chapter. s Variable length subnet mask support - OSPF considers both the IP address and subnet mask in determining the best route for a packet. An IP address mask is distributed with each advertised route. The mask indicates the range of addresses that are being described by the particular route. Including this mask enables the implementation of variable-length subnet masks (VLSMs), which means that a single IP network number can be subnetworked or broken up into many subnetworks of various sizes. When networks are subnetworked, OSPF forwards each IP packet to the network that is the best match for the packet's destination. It determines the best match by examining both the network address and the mask for each destination and finding the longest or most specific match. VLSM support is a key advantage for OSPF, especially when you consider the shortage of IP addresses. Another advantage is its flexibility. s Ability to import non-OSPF routing information - Connectivity from one autonomous system to another is achieved through OSPF autonomous system boundary routers (ASBRs). ASBRs can import external link advertisements that contain information about external networks from other protocols like RIP and redistribute them as LSAs to the OSPF network. In this way, ASBRs flood information about external networks to routers within the OSPF network. s Assurance of loop-free networks - The algorithm that dynamically calculates routing paths within the autonomous system does not generate a path with internal loops.

Section	Page
Contents	3
About This Guide	31
Audience	31
Scope of this Guide	32
Conventions	32
Switch 4007 Documentation	34
Documentation Comments	35
Year 2000 Compliance	35
Configuration Overview	39
Physical Configuration Requirements and Options	40
Requirements	40
Options	41
Order of Installation Activities	41
System Architecture	41
Management Options	42
Management Module Console	42
Switching Module Administration Console	43
Web Management software	43
SNMP-Based Network Management Overview	44
Management Access	45
Terminal Port Access	45
Modem Port Access	46
Access Levels	46
System Configuration Process	47
Configuration Procedure	47
Configure the Management Module	47
Configure Each Switching Module	47
Overview of the ManagementModule	53
Before You Start	53
Module Overview	54
Module Components	54
Module Functions	55
Impact on the Network	56
Installing Management Modules	57
Before You Start	57
Installing Modules	58
Hot Insert and HotSwap	58
Installing Non-Management Modules	58
Creating a Redundant Configuration	59
Installation	59
The Relationship Between Two Management Modules	59
The Failover Process	60
Connectivity Rules	61
Verifying Management Module Operation	62
The Display Button	63
Making Management Connections	63
Connecting to a 10BASE-T Ethernet Port	63
Using an MDI-to-MDI Crossover Cable	64
Connecting to an RS-232 Console Port	64
Using a Modem	66
Verifying Network Connectivity	67
EME Technical Specifications	69
Configuring and Using EME Options	71
Quick Reference Configuration	72
Saving Configuration Values	72
Connecting to the System	73
Initial Access	73
Logging into the System	73
Terminating a Connection	73
Setting Up an IP Address for Telnet	73
Connecting to Remote Devices	74
In-band Connections	75
Serial Line Internet Protocol Connections	75
Configuring Access to the Web Interface	76
Entering Commands	77
The Command Completion Feature	77
Listing Command Options	78
Keystroke Functions	80
Configuring the Terminal	81
Configuring the Terminal to Default Settings	81
Changing the Terminal Configuration	82
Customizing Terminal Settings	82
Setting Terminal Hangup	83
Setting Terminal Prompt	83
Setting Terminal Timeout Value	83
Setting Terminal Type	84
Troubleshooting the Terminal Interface	84
Customizing Your System	86
Assigning a UniqueName	86
Setting EME Diagnostics	86
Assigning a Contact Name and Location	86
Configuring the Internal Clock	87
Configuring User Logins	89
User Access Levels	89
User Login Functions	89
Login Limitations	89
Administer Access	89
Setting the Password	90
Adding New Users	90
Showing Current Users	91
Clearing Login Names	93
Configuring SNMP Values	94
Interaction Between the EME and SNMP	94
Setting Up IP Connectivity	94
Assigning an IP Address to the EME	94
Setting a Subnet Mask	95
Defining a Default Gateway	95
Showing and Clearing IP Settings	95
Creating a Community Table	96
Configuring a Trap Destination	97
Configuring the Authentication Alert Setting	97
Configuring Trap Options	97
Viewing SNMP Extensions and Traps	98
Interpreting EME Trap Messages	98
Obtaining More Information About SNMP	99
Configuring the Event Log	100
Using the File System	101
Software Configuration Files	101
Displaying Files in the File System	101
Deleting Specified Files From the File System	102
Deleting All Files and Resetting the Management Module	102
Resetting System Components	104
Resetting the Chassis	104
Resetting Switching Modules	104
Resetting the EME	105
Resetting the EME to Default Values	105
Accessing the Administration Console	106
Running Diagnostic Tests	107
Reporting Diagnostic Errors	108
Setting servdiag Characteristics	108
The cont_mode Characteristic	108
The loop_count Characteristic	108
The verbosity Characteristic	109
Displaying servdiag Characteristics	109
Obtaining Technical Assistance	109
Managing the Chassis Power and Temperature	111
Managing Power in the Chassis	112
Intelligent Power Subsystem Features	112
Load-Sharing Power Supplies	113
Power Non-Fault-Tolerant Mode	114
Power Fault-Tolerant Mode	114
Setting Power Fault-Tolerance	115
Enabling and Disabling Power to Slots	116
Power Class Settings	117
Using the Default Power Class Setting	117
Setting Power Class	117
Power Class 10 Warnings	118
Budgeting Power	118
Allocating Power for Installed Modules	118
Increasing the Unallocated Power Budget	119
Determining Chassis Power Budget	120
Power Supply Output in Non-Fault-Tolerant Mode	121
Power Supply Output in Fault-Tolerant Mode	121
Overheat Conditions	122
Enabling and Disabling Automatic Module Power-off	123
The Overheat Management Area	123
Overheat Power-off Process	124
Overheat Recovery Process	125
Saved Power Management Configurations	125
Displaying Operating Conditions	126
Displaying Chassis Information	126
Displaying Module Information	127
Basic Information For One Module	127
Basic Information For All Modules	127
Detailed Information For All Modules	127
Displaying Power Information	128
Displaying Chassis Inventory Information	129
Displaying EME Information	129
Module Parameters	133
Module Parameters Overview	134
Features	134
Benefits	134
Key Concepts	135
How to Set and Modify Module Parameters	135
Terminology	135
nvData	136
Physical Port Numbering	137
Slot Architecture	137
Default Port Settings	138
Configuring Port Status	139
Allocating Switch Fabric Capacity to Slots	140
9-port GEN Switch Fabric Module	140
Using Table33: Examples	140
24-port GEN Switch Fabric Module	141
Using Table34: Examples	142
Key Guidelines for Implementation	142
Effects of Removing a Module	143
VLAN Changes	143
Trunk Changes	143
Effects of Replacing Modules	144
Replacing Modules of the Same Type	144
Replacing Modules of Different Types	144
Ethernet	145
Ethernet Overview	146
Features	146
Benefits	147
Link Bandwidths	147
Link Availability	147
Other Benefits	147
Key Concepts	148
Ethernet Packet Processing	150
Key Guidelines for Implementation	152
Link Bandwidths	152
Trunks	152
Port Enable and Disable (Port State)	153
Important Considerations	153
Port Labels	153
Implementing PortLabels	153
Autonegotiation	154
Important Considerations	154
Port Mode	156
Important Considerations	156
Flow Control	157
Important Considerations	157
PACE Interactive Access	158
Important Considerations	158
Port Monitoring	158
Standards, Protocols, and Related Reading	159
Ethernet Protocol	159
Media Specifications	159
Related Reading	160
Bridge-Wide and Bridge Port Parameters	161
Bridging Overview	162
Benefits	162
Key Bridging Concepts	163
Learning Addresses	163
Aging Addresses	163
Forwarding, Filtering, and Flooding	164
Loop Detection and Network Resiliency	164
Bridging Implementation Summary	165
Key Guidelines for Implementation	167
Physical Ports and Bridge Ports	167
Option For FastAging	167
If You Want ToUseSTP	167
Port Forwarding Behavior	168
Routing Over BlockedSTP Ports	168
STP Compatible with Trunking	168
STP Not Compatible with Resilient Links	169
Bridge Ports and Trunks	169
Multicast Limits and Trunks	169
Bridge Port Addresses in Closed VLAN Mode	169
GVRP Usefulness	169
STP Terms and Concepts	170
Configuration Messages	170
Bridge Hierarchy	170
Actions That Result from CBPDU Information	171
Contents of CBPDUs	173
Comparing CBPDUs	173
How a Single Bridge Interprets CBPDUs	174
How Multiple Bridges Interpret CBPDUs	175
Determining the Root Bridge	178
Determining the Root Ports	178
Determining the Designated Bridge and Designated Ports	178
Spanning Tree PortStates	180
Reconfiguring the Bridged Network Topology	182
Resulting Actions	182
STP Bridge and Port Parameters	183
Bridge-wide STP Parameters	183
Bridge-Wide STP State	183
Bridge Priority	184
Bridge Maximum Age	184
Bridge Hello Time	184
Bridge Forward Delay	184
STP Group Address	185
Bridge Port STPParameters	186
Port State	186
Port Path Cost	186
Port Priority	186
MAC Address Table Design	187
Address Space	187
Important Considerations	187
Address Aging	189
Address Table Dependencies	189
Normal Aging Process	190
If the STP State isEnabled	190
STP Topology Change	190
Port Down Events	191
If the STP State isDisabled	191
If STP State is “AgingOnly”	192
Important Considerations	192
Frame Processing	194
IP Fragmentation	194
IPX SNAP Translation	195
Broadcast and Multicast Limits	195
Important Considerations	196
GARP VLAN Registration Protocol (GVRP)	197
Important Considerations	197
Standards, Protocols, and Related Reading	198
Class of Service (CoS)	199
Overview	200
Key Concepts	201
Basic Elements of theStandard	201
Format of PrioritizedPackets	202
Queues and PriorityLevels	202
CoS in Your System	203
CoS Architecture	203
Important Considerations	204
Configuring Priority Levels	204
Configuring a Rate Limit on Queue1	204
Important Considerations	205
Handling Tagged and Untagged Packets	206
Standards, Protocols, and Related Reading	206
IP Multicast Filtering with IGMP	207
Overview	208
Benefits	208
Key Concepts	210
Devices That Generate IP Multicast Packets	210
Group Addresses and Group Members	210
Communication Protocols	210
IP Multicast DeliveryProcess	211
How Routers and Switches UseIGMP	211
Tracking Group Member Locations	212
How Hosts Use IGMP	213
Host Membership Reports	213
Join Message	213
Leave-Group Messages	213
Report Suppression and Effect on Switch Activity	213
Configuring IGMP in Your System	214
Key Implementation Guidelines	215
ProcessingIP MulticastPackets	217
Effects of MAC Address Aliasing	218
Important Considerations	219
Operating as theQuerier	220
Locating Multicast Routers	220
Aging the IGMP Tables	221
Standards, Protocols, and Related Reading	221
Trunking	223
Trunking Overview	224
Features	224
Benefits	224
Key Concepts	225
Port Numbering in a Trunk	225
Trunk Control Message Protocol (TCMP)	226
Key Guidelines for Implementation	227
General Guidelines	227
Trunk Capacity Guidelines	229
Automatic Backplane Trunking	230
Important Considerations	230
Defining Trunks	231
Important Considerations	231
Modifying Trunks	233
Important Considerations	233
Removing Trunks	233
Important Consideration	233
Standards, Protocols, and Related Reading	234
Resilient Links	235
Resilient Links Overview	236
Features	237
Benefits	237
Key Concepts	237
Key Guidelines for Implementation	238
General Guidelines	238
Resilient Link Define and Modify	238
Important Considerations	238
Resilient LinkState	239
Important Considerations	239
Resilient Link ActivePort	239
Important Considerations	239
Resilient LinkRemove	239
Important Consideration	239
Virtual LANs (VLANs)	241
VLAN Overview	242
Need for VLANs	242
Benefits	243
VLANs on the Switch4007	243
Features	245
Key Concepts	246
Related Standards and Protocols	246
Tagging Types	247
VLAN IDs	248
Terminology	249
Key Guidelines for Implementation	250
Migration Path for Network-based VLANs	250
VLANs Created by Router Port IP Interfaces	252
Design Guidelines	253
Procedural Guidelines	254
Number of VLANs	256
Equation for VLANs on Multilayer Switching Modules	256
VLAN Aware Mode	258
General Guidelines	259
VLAN allOpen or allClosed Mode	261
Important Considerations	261
Modifying the VLAN Mode	263
Mode Requirements	264
Using allOpen Mode	265
Using allClosed Mode	265
Port-based VLANs	266
The Default VLAN	266
Modifying the Default VLAN	267
Trunking and the Default VLAN	268
User-Configured Port-based VLANs	270
Important Considerations	270
Example 1: A Single VLAN Configuration	271
Example 2: VLANs with Tagged Backplane Ports	272
Example 3: VLANs with Tagged Front-Panel Ports	274
Dynamic Port-based VLANs Using GVRP	277
Important Considerations	277
Example: GVRP	279
Protocol-based VLANs	280
Important Considerations	280
Selecting a Protocol Suite	281
Establishing Routing Between VLANs	282
Important Considerations	282
Example 1: Routing Between Multilayer Modules	283
Example 2: One-Armed Routing Configuration	286
Network-based IP VLANs	289
Important Considerations	289
Example: Network-based VLANs	290
Ignore STP Mode	293
Important Considerations	293
Example: Ignore STP Mode	293
Rules of VLAN Operation	295
Ingress Rules	295
Egress Rules	298
Standard Bridging Rules for Outgoing Frames	298
Tag Status Rules	298
Examples of Flooding and Forwarding Decisions	299
Example 1: Flooding Decisions for Protocol-based VLANs	299
Example 2: VLAN Exception Flooding	300
Rules for Network-based (Layer 3) VLANs	300
Example 3: Decisions for One Network-based VLAN	301
Modifying and Removing VLANs	302
Monitoring VLAN Statistics	303
Packet Filtering	305
Packet Filtering Overview	306
What Can You Filter?	306
When Is a Filter Applied? — Paths	307
Input Packet Filtering: Receive Path	307
Output Packet Filtering: Transmit Path	307
Internal Packet Filtering: Receive Internal Path	307
Path Assignment	308
Key Concepts	309
Standard Packet Filters	309
Custom Packet Filters	310
Important Considerations	311
Managing Packet Filters	311
Tools for Writing Filters	313
ASCII Text Editor	313
Built-in Line Editor	313
Web Management Filter Builder Tool	315
Downloading Custom Packet Filters	317
Setting Up Your Environment	317
Loading a Custom Filter on the Switch4007	318
The Packet Filtering Language	319
Principles for Writing a Custom Filter	319
How the Packet Filter Language Works	319
Procedure for Writing a Custom Filter	320
Packet Filter Opcodes	322
Implementing Sequential Tests in a Packet Filter	329
Common Syntax Errors	331
Custom Packet Filter Examples	333
Destination AddressFilter	333
Source Address Filter	333
Length Filter	333
Type Filter	334
Ethernet Type IPX and Multicast Filter	334
Multiple Destination Address Filter	334
Source Address and Type Filter	335
Accept XNS or IP Filter	335
XNS Routing Filter	335
Port Group Filter	336
Limits to Filter Size	336
Storage Rules for Preprocessed Packet Filters	336
Run-time Storage of Packet Filters	336
Using Port Groups in Custom Packet Filters	337
Port Group Packet Filter Example	337
Port Group Filter Operation	337
Port Group Management and Control Functions	340
Defining Port Groups	340
Important Considerations	340
Long Custom Filter Example	341
Filtering Problem	341
Packet Filter Solution	342
Packet Filter One	344
Packet Filter Two	345
Combining a Subset of the Filters	346
Combining All the Filters	347
Optimizing the Filter with Accept and Reject Commands	348
IP Routing	351
Routing Overview	352
Routing in a Subnetworked Environment	354
Integrating Bridging and Routing	355
Bridging and Routing Models	355
3Com Bridging and Routing	356
IP Routing Overview	358
Features and Benefits	359
Key Concepts	359
Multiple IP Interfaces per VLAN	359
Media Access Control (MAC) Address	360
Network-Layer Address	360
IP Addresses	360
Dotted Decimal Notation	361
Network Portion	361
Subnetwork Portion	362
Subnet Mask Numbering	363
Variable Length Subnet Masks (VLSMs)	364
How VLSMs Work	364
Guidelines for Using VLSMs	364
Router Interfaces	365
Routing Table	366
Default Route	368
Routing Models: Port-based and VLAN-based	368
Key Guidelines for Implementing IP Routing	369
Configure Trunks (Optional)	369
Configure IP VLANs	370
Establish Your IP Interfaces	370
Interface Parameters	370
Important Consideration	371
Defining an IP Interface	371
Enable IP Routing	372

Match case Limit results 1 per page

452

HAPTER

19: O

PEN

HORTEST

ATH

IRST

(OSPF) R

OUTING

■

Support for virtual links to noncontiguous areas

— As discussed

earlier, OSPF can partition large autonomous systems into smaller,

more manageable subdivisions, called areas. An OSPF backbone is

responsible for distributing routing information between the areas of

an autonomous system. This backbone itself has all the properties of

an area and consists of those networks that are not contained in any

area. Although the backbone must be contiguous, backbone routers

can also be connected by means of a virtual link. Virtual links can be

configured between any two backbone routers that have an interface

to a common nonbackbone area. OSPF treats two routers that are

joined by a virtual link as if they were connected by an unnumbered

point-to-point network. For more information, see “Virtual Links”

later in this chapter.

■

Variable length subnet mask support

— OSPF considers both the

IP address and subnet mask in determining the best route for a

packet. An IP address mask is distributed with each advertised route.

The mask indicates the range of addresses that are being described by

the particular route. Including this mask enables the implementation

of variable-length subnet masks (VLSMs), which means that a single IP

network number can be

subnetworked

or broken up into many

subnetworks of various sizes. When networks are subnetworked,

OSPF forwards each IP packet to the network that is the best match

for the packet’s destination. It determines the best match by

examining both the network address and the mask for each

destination and finding the longest or most specific match. VLSM

support is a key advantage for OSPF, especially when you consider the

shortage of IP addresses. Another advantage is its flexibility.

■

Ability to import non-OSPF routing information

— Connectivity

from one autonomous system to another is achieved through OSPF

autonomous system boundary routers (ASBRs). ASBRs can import

external link advertisements that contain information about external

networks from other protocols like RIP and redistribute them as LSAs

to the OSPF network. In this way, ASBRs flood information about

external networks to routers within the OSPF network.

■

Assurance of loop-free networks

— The algorithm that

dynamically calculates routing paths within the autonomous system

does not generate a path with internal loops.