H3c-technologies H3C S5120 Series Switches User Manual Page 216
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1-2
Enabling Forwarding of Directed Broadcasts to a Directly Connected Network
If a device is enabled to receive directed broadcasts, the device will determine whether to forward them
according to the configuration on the outgoing interface.
Follow these steps to enable the device to forward directed broadcasts:
To do… Use the command… Remarks
Enter system view
system-view
—
Enter interface view
interface interface-type
interface-number
—
Enable the interface to forward
directed broadcasts
ip forward-broadcast [ acl
acl-number ]
Required
By default, the device is
disabled from forwarding
directed broadcasts.
z If an ACL is referenced in the ip forward-broadcast [ acl-number ] command, only packets
permitted by the ACL can be forwarded.
z If you repeatedly execute the ip forward-broadcast acl [ acl-number ] command on an interface,
the last executed command takes effect only. If the command executed last time does not include
the acl acl-number, the ACL configured previously will be removed.
Configuring TCP Attributes
Enabling the SYN Cookie Feature
As a general rule, the establishment of a TCP connection involves the following three handshakes:
1) The request originator sends a SYN message to the target server.
2) After receiving the SYN message, the target server establishes a TCP connection in the
SYN_RECEIVED state, returns a SYN ACK message to the originator, and waits for a response.
3) After receiving the SYN ACK message, the originator returns an ACK message. Thus, the TCP
connection is established.
Attackers may mount SYN Flood attacks during TCP connection establishment. They send a large
number of SYN messages to the server to establish TCP connections, but they never make any
response to SYN ACK messages. As a result, a large amount of incomplete TCP connections are
established, resulting in heavy resource consumption and making the server unable to handle services
normally.
The SYN Cookie feature can prevent SYN Flood attacks. After receiving a TCP connection request, the
server directly returns a SYN ACK message, instead of establishing an incomplete TCP connection.
Only after receiving an ACK message from the client can the server establish a connection, and then
enter the ESTABLISHED state. In this way, large amounts of incomplete TCP connections could be
avoided to protect the server against SYN Flood attacks.
- Configuration Guide 1
- All Rights Reserved 2
- Trademarks 2
- Preface 3
- 1 About This Document 4
- Conventions 8
- 2 Documentation Guide 9
- Technical Support 10
- Documentation Feedback 10
- 3 Product Features 11
- Distribution Layer Switches 12
- Access Switches 12
- S9500/S7500E 13
- S5120-SI 13
- Core/Aggregation 13
- 1 CLI Configuration 15
- Entering CLI Through Telnet 20
- Command Conventions 21
- CLI View Description 22
- Command View Reference 23
- Login command views 24
- Tips on Using the CLI 28
- Typing and Editing Commands 29
- Undo Form of a Command 31
- Controlling CLI Display 31
- Saving Configurations 34
- Supported User Interfaces 37
- User Interface Number 37
- Common Configuration 42
- Password 47
- Logging In Through SSH 66
- Management System 67
- Displaying Web Users 68
- 5 Logging In Through NMS 70
- Packets 72
- 7 Controlling Login Users 73
- [Sysname] ip http acl 2030 80
- Ethernet Port Configuration 82
- Configuring a Port Group 86
- Configuration 95
- Null Interface 96
- Operational key 100
- Configuration classes 100
- Reference port 101
- LACP protocol 101
- Link aggregation modes 102
- Selecting a reference port 103
- Configuration Guidelines 106
- Network requirements 110
- Configuration procedure 110
- Table of Contents 115
- Port Isolation Configuration 116
- Networking requirements 117
- Port Mirroring Configuration 120
- 1 LLDP Configuration 125
- LLDPDUs 127
- How LLDP Works 129
- LLDP Configuration Task List 130
- Enabling LLDP 131
- Enabling LLDP Polling 132
- Configuration Prerequisites 135
- Configuring LLDP Trapping 136
- LLDP Configuration Examples 137
- LLDP status on Switch A 139
- 3) Verify the configuration 141
- 1 VLAN Configuration 143
- VLAN Fundamentals 144
- Types of VLAN 145
- Port link type 147
- Default VLAN 147
- interface vlan-interface 151
- [ vlan-interface-id ] 151
- [ interface-type 151
- VLAN Configuration Example 152
- Verification 153
- 2 Voice VLAN Configuration 154
- Voice VLAN Assignment Modes 155
- Configuring a Voice VLAN 158
- 1 MSTP Configuration 166
- Basic Concepts in STP 167
- How STP works 168
- STP timers 173
- Introduction to RSTP 174
- Introduction to MSTP 174
- Basic Concepts in MSTP 175
- Common root bridge 177
- Boundary port 177
- Roles of ports 177
- Port states 178
- How MSTP Works 179
- MSTP Configuration Task List 180
- Configuring MSTP 181
- Configuring Timers of MSTP 185
- Configuration example 190
- Configuring Port Priority 191
- Enabling the MSTP Feature 193
- Performing mCheck 194
- Configuration Procedure 195
- Configuration Example 195
- Configuring Digest Snooping 196
- GE1/0/2 GE1/0/2 198
- Configuration prerequisites 200
- Enabling BPDU guard 200
- Enabling Root guard 201
- Enabling Loop guard 202
- Enabling TC-BPDU guard 203
- MSTP Configuration Example 204
- Figure 1-13 207
- IP Addressing Configuration 210
- Special IP Addresses 211
- Subnetting and Masking 211
- Configuring IP Addresses 212
- Directly Connected Network 215
- Configuring TCP Attributes 216
- 1 ARP Configuration 222
- ARP Operation 223
- Configuring ARP 224
- Enabling the ARP Entry Check 226
- ARP Configuration Example 226
- Configuring Gratuitous ARP 227
- Introduction 229
- Configuring ARP Detection 231
- Man-in-the-middle attack 232
- ARP detection mechanism 232
- Application Environment 241
- Fundamentals 241
- Enabling DHCP 243
- Prerequisites 247
- Symptom 251
- Analysis 251
- Solution 251
- 2 DHCP Client Configuration 252
- DHCP Snooping Configuration 254
- Untrusted Untrusted 255
- BOOTP Client Configuration 262
- Through BOOTP 263
- Network requirement 264
- 1 FTP Configuration 266
- Configuring the FTP Client 267
- Configuring the FTP Server 273
- 2 TFTP Configuration 278
- Configuring the TFTP Client 279
- IP Routing and Routing Table 284
- Static Routing Configuration 288
- Configuring a Static Route 289
- 1 Multicast Overview 295
- Broadcast 296
- Multicast 297
- Features of Multicast 298
- Advantages of multicast 299
- Applications of multicast 299
- Multicast Models 300
- Multicast Architecture 300
- Multicast Addresses 301
- Multicast Protocols 303
- Layer 2 multicast protocols 304
- IGMP Snooping Configuration 306
- GE1/0/1 GE1/0/2 307
- How IGMP Snooping Works 308
- IGMP Snooping Proxying 310
- Protocols and Standards 311
- Enabling IGMP Snooping 312
- Configuring Static Ports 315
- Multicast VLAN Configuration 338
- Configuring Multicast VLAN 339
- Network requirements 342
- Network diagram 343
- 1 QoS Overview 348
- QoS Techniques Overview 349
- 2 QoS Policy Configuration 350
- Defining a Traffic Behavior 352
- Defining a Policy 352
- Applying the QoS Policy 353
- Priority Mapping Overview 355
- Priority Mapping Tables 356
- Priority Mapping Procedure 356
- Configuring Priority Mapping 357
- 4 Line Rate Configuration 361
- <Sysname> system-view 362
- SP queuing 364
- WRR queuing 364
- Configuring SP Queuing 366
- Configure WRR Queuing 367
- Configuring SP+WRR Queuing 368
- Traffic Filtering Overview 370
- Traffic Redirecting Overview 373
- 8 Appendix 374
- 802.1p Priority 376
- 1 802.1X Configuration 379
- Basic Concepts of 802.1X 380
- EAP over LAN 381
- EAP Packet Format 382
- EAP over RADIUS 383
- EAP relay 384
- EAP termination 386
- 802.1X Access Control Method 387
- 802.1X Timers 387
- VLAN assignment 388
- Guest VLAN 389
- Auth-Fail VLAN 389
- ACL assignment 390
- 802.1X Basic Configuration 391
- Enabling 802.1X for a port 392
- Enabling the Quiet Timer 394
- Configuring a Guest VLAN 395
- 802.1X Configuration Example 397
- Internet 400
- 1 AAA Configuration 407
- Introduction to RADIUS 408
- RADIUS Packet Format 410
- AAA Configuration Task List 414
- Configuring AAA 415
- [ flow ] 416
- Configuring RADIUS 424
- Creating a RADIUS Scheme 425
- 430
- AAA Configuration Examples 434
- Troubleshooting AAA 444
- 1 PKI Configuration 447
- Architecture of PKI 448
- Applications of PKI 449
- Operation of PKI 449
- PKI Configuration Task List 450
- Configuring an Entity DN 450
- Configuring a PKI Domain 452
- Deleting a Certificate 457
- PKI Configuration Examples 459
- Troubleshooting PKI 467
- Failed to Retrieve CRLs 468
- 1 SSL Configuration 470
- SSL Protocol Stack 471
- SSL Configuration Task List 472
- Troubleshooting SSL 476
- 1 SSH2.0 Configuration 479
- Version negotiation 480
- Authentication 481
- Session request 482
- Interaction 482
- Configuring an SSH User 485
- 192.168.0.2/24 490
- Vlan-int1 490
- 192.168.0.1/24 490
- 2 SFTP Service 501
- Configuring an SFTP Client 502
- Working with SFTP Files 504
- Displaying Help Information 504
- 1 Public Key Configuration 512
- 2) Configure Device B 517
- 1 HABP Configuration 522
- Configuring HABP 523
- HABP Configuration Example 524
- 1 ACL Configuration 527
- ACL Classification 528
- ACL Numbering and Naming 528
- Match Order 528
- ACL Rule Numbering Step 529
- ACL Configuration Task List 530
- Configuring an ACL 531
- Configuring an Advanced ACL 533
- Copying an ACL 535
- ACL Configuration Examples 537
- 1 Device Management 539
- Rebooting a Device 540
- Upgrading Device Software 542
- 1 NTP Configuration 550
- Advantages of NTP 551
- How NTP Works 551
- NTP Message Format 552
- Operation Modes of NTP 554
- Broadcast mode 555
- Multicast mode 555
- NTP Configuration Task List 556
- NTP Configuration Examples 565
- Root delay: 31.00 ms 571
- delay disper 571
- 1 SNMP Configuration 577
- SNMP Protocol Version 578
- MIB Overview 578
- SNMP Configuration 579
- Configuring SNMP Logging 581
- Configuring SNMP Trap 582
- Configuring Trap Parameters 583
- SNMPv3 Configuration Example 586
- 2 MIB Style Configuration 589
- 1 RMON Configuration 591
- Working Mechanism 592
- RMON Groups 592
- Private alarm group 593
- History group 593
- Ethernet statistics group 593
- 1 File System Management 602
- Directory Operations 603
- File Operations 604
- Copying a File 605
- Moving a File 605
- Deleting a File 605
- Batch Operations 606
- Storage Medium Operations 606
- Checking files 607
- <Sysname> cd 609
- <Sysname> pwd 609
- Configuration File Overview 610
- Configuration Task List 613
- Configuring Ping 620
- Ping Configuration Example 621
- Tracert 623
- System Debugging 624
- Configuring System Debugging 625
- 1 Basic Configurations 628
- Configuring the Device Name 629
- Configuring the System Clock 629
- Displaying the system clock 630
- " is in 632
- Configuring a Banner 633
- Configuring CLI Hotkeys 634
- Modifying command level 641
- Information Center Overview 644
- System Information Format 648
- Overview 665
- Mac address aging time: 500s 671
- Cluster Management Overview 673
- How a Cluster Works 674
- Introduction to NDP 675
- Introduction to NTDP 675
- DisconnectConnect 676
- Management VLAN 677
- Configuring NDP Parameters 679
- Configuring NTDP Parameters 680
- Establishing a Cluster 681
- Devices Within a Cluster 683
- Cluster Member Management 684
- Member Devices 685
- 1 HTTP Configuration 695
- Enabling the HTTP Service 696
- HTTP Configuration Example 697
- 2 HTTPS Configuration 699
- Enabling the HTTPS Service 700
- Control Policy 701
- HTTPS Configuration Example 702
- 1 Stack Configuration 707
- Establishing a Stack 708
- Configuring Stack Ports 709
- Creating a Stack 709
- Stack Configuration Example 710
- 1 PoE Configuration 714
- PoE Configuration Task List 715
- Enabling PoE 716
- Detecting PDs 717
- Configuring the PoE Power 718
- Monitoring PD 720
- Configuring PoE Profile 720
- Applying PoE Profile 721
- PoE Configuration Example 722
- Troubleshooting PoE 724
- IP Source Guard Overview 726
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