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Transparent Mode, 4.6.1. Overview of Transparent Mode, 4.6.2. Comparison with Routing mode

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4.6. Transparent Mode Chapter 4. Routing 4.6. Transparent Mode 4.6.1. Overview of Transparent Mode Deploying D-Link Firewalls operating in Transparent Mode into an existing network topology can significantly strengthen security. It is simple to do and doesn't require reconfiguration of existing nodes. Once deployed, NetDefendOS can then allow or deny access to different types of services (for example HTTP) and in specified directions. As long as users of the network are accessing permitted services through the D-Link Firewall they are not aware of its presence. Transparent Mode is enabled by specifying a Switch Route instead of a standard Route. A typical example of Transparent Mode's ability to improve security is in a corporate environment where there might be a need to protect different departments from one another. The finance department might require access to only a restricted set of services (HTTP for example) on the sales department's servers whilst the sales department might require access to a similarly restricted set of applications on the finance department's network. By deploying a single D-Link Firewall between the two department's networks, transparent but controlled access can be achieved using the Transparent Mode feature. Another example might be an organisation allowing traffic between the external Internet and a range of public IP address' on an internal network. Transparent mode can control what kind of service is permitted to these IP addresses and in what direction. For instance the only services permitted in such a situation may be HTTP access out to the Internet. 4.6.2. Comparison with Routing mode The D-Link Firewall can operate in two modes: Routing Mode or Transparent Mode. In Routing Mode, the D-Link Firewall performs all the functions of a Layer 3 router; if the firewall is placed into a network for the first time, or if network topology changes, the routing configuration must therefore be thoroughly checked to ensure that the routing table is consistent with the new layout. Reconfiguration of IP settings may be required for pre-existing routers and protected servers. This mode works well when complete control over routing is desired. In Transparent Mode, where Switch Route is used instead of Route, the firewall acts in a way that has similarities to a switch; it screens IP packets and forwards them transparently to the correct interface without modifying any of the source or destination information on the IP or Ethernet levels. Two benefits of Transparent Mode are: • When a client moves from one interface to another without changing IP address, it can still obtain the same services as before (for example HTTP, FTP) without routing reconfiguration. • The same network address range can exist on several interfaces. Note D-Link Firewalls need not operate exclusively in Transparent Mode but can combine Transparent Mode with Routing Mode to operate in a hybrid mode. That is to say, the firewall can have both Switch Routes as well as standard routes defined. It is also possible to create a hybrid case by applying address translation on otherwise transparent traffic. 4.6.3. Transparent Mode Implementation In transparent mode, NetDefendOS allows ARP transactions to pass through the D-Link Firewall, and determines from this ARP traffic the relationship between IP addresses, physical addresses and interfaces. NetDefendOS remembers this address information in order to relay IP packets to the correct receiver. During the ARP transactions, neither of the endpoints will be aware of the firewall's presence. 119

Section	Page
User Manual	3
Table of Contents	4
Preface	12
Chapter 1. Product Overview	14
1.1. About D-Link NetDefendOS	14
1.2. NetDefendOS Architecture	16
1.2.1. State-based Architecture	16
1.2.2. NetDefendOS Building Blocks	16
1.2.3. Basic Packet Flow	17
1.3. NetDefendOS State Engine Packet Flow	19
Chapter 2. Management and Maintenance	23
2.1. Managing NetDefendOS	23
2.1.1. Overview	23
2.1.2. Default Administrator Accounts	23
2.1.3. The CLI	24
2.1.4. The WebUI	26
2.1.5. Working with Configurations	29
2.2. Events and Logging	35
2.2.1. Overview	35
2.2.2. Event Messages	35
2.2.3. Event Message Distribution	35
2.2.3.1. Logging to Syslog Hosts	36
2.2.3.2. SNMP Traps	37
2.3. RADIUS Accounting	39
2.3.1. Overview	39
2.3.2. RADIUS Accounting Messages	39
2.3.3. Interim Accounting Messages	41
2.3.4. Activating RADIUS Accounting	41
2.3.5. RADIUS Accounting Security	41
2.3.6. RADIUS Accounting and High Availability	41
2.3.7. Handling Unresponsive Servers	42
2.3.8. Accounting and System Shutdowns	42
2.3.9. Limitations with NAT	42
2.4. Monitoring	43
2.4.1. SNMP Monitoring	43
2.5. Maintenance	45
2.5.1. Auto-Update Mechanism	45
2.5.2. Configuration Backup and Restore	45
2.5.3. Resetting to Factory Defaults	45
Chapter 3. Fundamentals	48
3.1. The Address Book	48
3.1.1. Overview	48
3.1.2. IP Addresses	48
3.1.3. Ethernet Addresses	50
3.1.4. Address Groups	51
3.1.5. Auto-Generated Address Objects	51
3.2. Services	52
3.2.1. Overview	52
3.2.2. TCP and UDP Based Services	53
3.2.3. ICMP Services	55
3.2.4. Custom IP Protocol Services	55
3.3. Interfaces	57
3.3.1. Overview	57
3.3.2. Ethernet	58
3.3.3. VLAN	60
3.3.4. PPPoE	61
3.3.4.1. Overview of PPP	61
3.3.4.2. PPPoE Client Configuration	62
3.3.5. GRE Tunnels	63
3.3.6. Interface Groups	66
3.4. ARP	68
3.4.1. Overview	68
3.4.2. ARP in NetDefendOS	68
3.4.3. ARP Cache	68
3.4.4. Static and Published ARP Entries	69
3.4.5. Advanced ARP Settings	71
3.5. The IP Rule Set	73
3.5.1. Security Policies	73
3.5.2. IP Rule Evaluation	74
3.5.3. IP Rule Actions	75
3.5.4. Editing IP rule set Entries	76
3.6. Schedules	77
3.7. X.509 Certificates	79
3.7.1. Overview	79
3.7.2. X.509 Certificates in NetDefendOS	80
3.8. Setting Date and Time	82
3.8.1. General Date and Time Settings	82
3.8.2. Time Servers	83
3.9. DNS Lookup	87
Chapter 4. Routing	89
4.1. Overview	89
4.2. Static Routing	90
4.2.1. Basic Principles of Routing	90
4.2.2. Static Routing	91
4.2.3. Route Failover	94
4.2.4. Proxy ARP	96
4.3. Policy-based Routing	98
4.3.1. Overview	98
4.3.2. Policy-based Routing Tables	98
4.3.3. Policy-based Routing Rules	98
4.3.4. Policy-based Routing Table Selection	99
4.3.5. The Ordering parameter	99
4.4. Dynamic Routing	103
4.4.1. Dynamic Routing overview	103
4.4.2. OSPF	104
4.4.3. Dynamic Routing Policy	107
4.5. Multicast Routing	110
4.5.1. Overview	110
4.5.2. Multicast Forwarding using the SAT Multiplex Rule	110
4.5.2.1. Multicast Forwarding - No Address Translation	111
4.5.2.2. Multicast Forwarding - Address Translation Scenario	112
4.5.3. IGMP Configuration	114
4.5.3.1. IGMP Rules Configuration - No Address Translation	115
4.5.3.2. IGMP Rules Configuration - Address Translation	116
4.6. Transparent Mode	119
4.6.1. Overview of Transparent Mode	119
4.6.2. Comparison with Routing mode	119
4.6.3. Transparent Mode Implementation	119
4.6.4. Enabling Transparent Mode	120
4.6.5. High Availability with Transparent Mode	120
4.6.6. Transparent Mode Scenarios	120
Chapter 5. DHCP Services	127
5.1. Overview	127
5.2. DHCP Servers	128
5.3. Static DHCP Assignment	130
5.4. DHCP Relaying	131
5.5. IP Pools	132
Chapter 6. Security Mechanisms	135
6.1. Access Rules	135
6.1.1. Introduction	135
6.1.2. IP spoofing	135
6.1.3. Access Rule Settings	136
6.2. Application Layer Gateways	138
6.2.1. Overview	138
6.2.2. HTTP	139
6.2.3. FTP	140
6.2.4. TFTP	145
6.2.5. SMTP	146
6.2.5.1. DNSBL SPAM Filtering	147
6.2.6. POP3	151
6.2.7. SIP	152
6.2.8. H.323	155
6.3. Web Content Filtering	169
6.3.1. Overview	169
6.3.2. Active Content Handling	169
6.3.3. Static Content Filtering	170
6.3.4. Dynamic Web Content Filtering	172
6.3.4.1. Content Filtering Categories	176
6.4. Anti-Virus Scanning	183
6.4.1. Overview	183
6.4.2. Implementation	183
6.4.3. Activating Anti-Virus Scanning	184
6.4.4. The Signature Database	184
6.4.5. Subscribing to the D-Link Anti-Virus Service	184
6.4.6. Anti-Virus Options	184
6.5. Intrusion Detection and Prevention	188
6.5.1. Overview	188
6.5.2. IDP Availability in D-Link Models	188
6.5.3. IDP Rules	190
6.5.4. Insertion/Evasion Attack Prevention	191
6.5.5. IDP Pattern Matching	192
6.5.6. IDP Signature Groups	192
6.5.7. IDP Actions	194
6.5.8. SMTP Log Receiver for IDP Events	194
6.6. Denial-Of-Service (DoS) Attacks	198
6.6.1. Overview	198
6.6.2. DoS Attack Mechanisms	198
6.6.3. Ping of Death and Jolt Attacks	198
6.6.4. Fragmentation overlap attacks: Teardrop, Bonk, Boink and Nestea	199
6.6.5. The Land and LaTierra attacks	199
6.6.6. The WinNuke attack	199
6.6.7. Amplification attacks: Smurf, Papasmurf, Fraggle	200
6.6.8. TCP SYN Flood Attacks	201
6.6.9. The Jolt2 Attack	201
6.6.10. Distributed DoS Attacks	201
6.7. Blacklisting Hosts and Networks	202
Chapter 7. Address Translation	204
7.1. Dynamic Network Address Translation	204
7.2. NAT Pools	207
7.3. Static Address Translation	210
7.3.1. Translation of a Single IP Address (1:1)	210
7.3.2. Translation of Multiple IP Addresses (M:N)	213
7.3.3. All-to-One Mappings (N:1)	215
7.3.4. Port Translation	216
7.3.5. Protocols handled by SAT	216
7.3.6. Multiple SAT rule matches	217
7.3.7. SAT and FwdFast Rules	217
Chapter 8. User Authentication	220
8.1. Overview	220
8.2. Authentication Setup	221
8.2.1. Setup Summary	221
8.2.2. The Local Database	221
8.2.3. External Authentication Servers	221
8.2.4. Authentication Rules	222
8.2.5. Authentication Processing	223
8.2.6. HTTP Authentication	223
Chapter 9. VPN	229
9.1. Overview	229
9.1.1. The Need for VPNs	229
9.1.2. VPN Encryption	229
9.1.3. VPN Planning	229
9.1.4. Key Distribution	230
9.2. VPN Quickstart Guide	231
9.2.1. IPsec LAN to LAN with Pre-shared Keys	231
9.2.2. IPsec Roaming Clients with Pre-shared Keys	232
9.2.3. IPsec Roaming Clients with Certificates	234
9.2.4. L2TP Roaming Clients with Pre-Shared Keys	234
9.2.5. L2TP Roaming Clients with Certificates	236
9.2.6. PPTP Roaming Clients	236
9.2.7. VPN Troubleshooting	237
9.3. IPsec	240
9.3.1. Overview	240
9.3.2. Internet Key Exchange (IKE)	240
9.3.3. IKE Authentication	245
9.3.4. IPsec Protocols (ESP/AH)	247
9.3.5. NAT Traversal	248
9.3.6. Proposal Lists	249
9.3.7. Pre-shared Keys	250
9.3.8. Identification Lists	251
9.4. IPsec Tunnels	253
9.4.1. Overview	253
9.4.2. LAN to LAN Tunnels with Pre-shared Keys	253
9.4.3. Roaming Clients	253
9.4.3.1. PSK based client tunnels	254
9.4.3.2. Self-signed Certificate based client tunnels	255
9.4.3.3. CA Server issued Certificates based client tunnels	256
9.4.3.4. Using Config Mode	257
9.4.4. Fetching CRLs from an alternate LDAP server	259
9.5. PPTP/L2TP	260
9.5.1. PPTP	260
9.5.2. L2TP	261
Chapter 10. Traffic Management	267
10.1. Traffic Shaping	267
10.1.1. Introduction	267
10.1.2. Traffic Shaping in NetDefendOS	268
10.1.3. Simple Bandwidth Limiting	269
10.1.4. Limiting Bandwidth in Both Directions	270
10.1.5. Creating Differentiated Limits with Chains	271
10.1.6. Precedences	272
10.1.7. Guarantees	274
10.1.8. Differentiated Guarantees	274
10.1.9. Groups	275
10.1.10. Recommendations	276
10.1.11. A Summary of Traffic Shaping	277
10.2. Threshold Rules	279
10.2.1. Overview	279
10.2.2. Connection Rate/Total Connection Limiting	279
10.2.3. Grouping	279
10.2.4. Rule Actions	279
10.2.5. Multiple Triggered Actions	280
10.2.6. Exempted Connections	280
10.2.7. Threshold Rules and ZoneDefense	280
10.2.8. Threshold Rule Blacklisting	280
10.3. Server Load Balancing	281
10.3.1. Overview	281
10.3.2. Identifying the Servers	282
10.3.3. The Load Distribution Mode	282
10.3.4. The Distribution Algorithm	282
10.3.5. Server Health Monitoring	284
10.3.6. SLB_SAT Rules	284
Chapter 11. High Availability	289
11.1. Overview	289
11.2. High Availability Mechanisms	291
11.3. High Availability Setup	293
11.3.1. Hardware Setup	293
11.3.2. NetDefendOS Setup	294
11.3.3. Verifying Cluster Functioning	294
11.4. High Availability Issues	296
Chapter 12. ZoneDefense	298
12.1. Overview	298
12.2. ZoneDefense Switches	299
12.3. ZoneDefense Operation	300
12.3.1. SNMP	300
12.3.2. Threshold Rules	300
12.3.3. Manual Blocking and Exclude Lists	300
12.3.4. Limitations	302
Chapter 13. Advanced Settings	304
13.1. IP Level Settings	304
13.2. TCP Level Settings	307
13.3. ICMP Level Settings	311
13.4. ARP Settings	312
13.5. Stateful Inspection Settings	314
13.6. Connection Timeouts	316
13.7. Size Limits by Protocol	318
13.8. Fragmentation Settings	320
13.9. Local Fragment Reassembly Settings	324
13.10. DHCP Settings	325
13.11. DHCPRelay Settings	326
13.12. DHCPServer Settings	327
13.13. IPsec Settings	328
13.14. Logging Settings	330
13.15. Time Synchronization Settings	331
13.16. PPP Settings	333
13.17. Hardware Monitor Settings	334
13.18. Packet Re-assembly Settings	335
13.19. Miscellaneous Settings	336
Appendix A. Subscribing to Security Updates	338
Appendix B. IDP Signature Groups	340
Appendix C. Checked MIME filetypes	344
Appendix D. The OSI Framework	348
Appendix E. D-Link worldwide offices	349

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4.6. Transparent Mode

4.6.1. Overview of Transparent Mode

Deploying D-Link Firewalls operating in Transparent Mode into an existing network topology can

significantly strengthen security. It is simple to do and doesn't require reconfiguration of existing

nodes. Once deployed, NetDefendOS can then allow or deny access to different types of services

(for example HTTP) and in specified directions. As long as users of the network are accessing

permitted services through the D-Link Firewall they are not aware of its presence. Transparent

Mode is enabled by specifying a

Switch Route

instead of a standard

Route.

A typical example of Transparent Mode's ability to improve security is in a corporate environment

where there might be a need to protect different departments from one another. The finance

department might require access to only a restricted set of services (HTTP for example) on the sales

department's servers whilst the sales department might require access to a similarly restricted set of

applications on the finance department's network. By deploying a single D-Link Firewall between

the two department's networks, transparent but controlled access can be achieved using the

Transparent Mode feature.

Another example might be an organisation allowing traffic between the external Internet and a range

of public IP address' on an internal network. Transparent mode can control what kind of service is

permitted to these IP addresses and in what direction. For instance the only services permitted in

such a situation may be HTTP access out to the Internet.

4.6.2. Comparison with Routing mode

The D-Link Firewall can operate in two modes: Routing Mode or Transparent Mode. In Routing

Mode, the D-Link Firewall performs all the functions of a Layer 3 router; if the firewall is placed

into a network for the first time, or if network topology changes, the routing configuration must

therefore be thoroughly checked to ensure that the routing table is consistent with the new layout.

Reconfiguration of IP settings may be required for pre-existing routers and protected servers. This

mode works well when complete control over routing is desired.

In Transparent Mode, where

Switch Route

is used instead of

Route

, the firewall acts in a way that

has similarities to a switch; it screens IP packets and forwards them transparently to the correct

interface without modifying any of the source or destination information on the IP or Ethernet

levels. Two benefits of Transparent Mode are:

•

When a client moves from one interface to another without changing IP address, it can still

obtain the same services as before (for example HTTP, FTP) without routing reconfiguration.

•

The same network address range can exist on several interfaces.

Note

D-Link Firewalls need not operate exclusively in Transparent Mode but can combine

Transparent Mode with Routing Mode to operate in a hybrid mode. That is to say, the

firewall can have both

Switch Route

s as well as standard routes defined. It is also

possible to create a hybrid case by applying address translation on otherwise

transparent traffic.

4.6.3. Transparent Mode Implementation

In transparent mode, NetDefendOS allows ARP transactions to pass through the D-Link Firewall,

and determines from this ARP traffic the relationship between IP addresses, physical addresses and

interfaces. NetDefendOS remembers this address information in order to relay IP packets to the

correct receiver. During the ARP transactions, neither of the endpoints will be aware of the

firewall's presence.

4.6. Transparent Mode

Chapter 4. Routing

119