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Chapter 10 Firewalls
NN47923-500
These custom rules work by evaluating the network traffic source IP address,
destination IP address, IP protocol type, and comparing these to rules set by the
administrator.
Below is a brief technical description of how these connections are tracked.
Connections can either be defined by the upper protocols (for instance, TCP), or
by the Business Secure Router itself (as with the virtual connections created for
UDP and ICMP).
TCP security
The Business Secure Router uses state information embedded in TCP packets.
The first packet of any new connection has its SYN flag set and its ACK flag
cleared; these are initiation packets. All packets that do not have this flag structure
are called subsequent packets, since they represent data that occurs later in the
TCP stream.
If an initiation packet originates on the WAN, someone is trying to make a
connection from the Internet into the LAN. Except in a few special cases, (see
“Upper layer protocols” on page 165
), these packets are dropped and logged.
If an initiation packet originates on the LAN, someone is trying to make a
connection from the LAN to the Internet. Assuming that this is an acceptable part
of the security policy (as is the case with the default policy), the connection is
allowed. A cache entry is added, which includes connection information such as
IP addresses, TCP ports, and sequence numbers.
After the Business Secure Router receives any subsequent packet (from the
Internet or from the LAN), its connection information is extracted and checked
against the cache. A packet is only allowed to pass through if it corresponds to a
valid connection (that is, if it is a response to a connection that originated on the
LAN).
Note:
The ability to define firewall rules is a very powerful tool. Using
custom rules, it is possible to disable all firewall protection or block all
access to the Internet. Use extreme caution when creating or deleting
firewall rules. Test changes after creating them to make sure they work
correctly.
Содержание BSR252
Страница 28: ...28 Tables NN47923 500 ...
Страница 44: ...44 Chapter 1 Getting to know your Business Secure Router NN47923 500 ...
Страница 52: ...52 Chapter 2 Introducing the WebGUI NN47923 500 ...
Страница 70: ...70 Chapter 3 Wizard setup NN47923 500 ...
Страница 91: ...Chapter 5 System screens 91 Nortel Business Secure Router 252 Configuration Basics Figure 20 Time and Date ...
Страница 96: ...96 Chapter 5 System screens NN47923 500 ...
Страница 100: ...100 Chapter 6 LAN screens NN47923 500 Configuring IP Click LAN to open the IP screen Figure 22 LAN IP ...
Страница 111: ...Chapter 7 WAN screens 111 Nortel Business Secure Router 252 Configuration Basics Figure 26 WAN WAN ISP ...
Страница 114: ...114 Chapter 7 WAN screens NN47923 500 Figure 27 WAN IP ...
Страница 120: ...120 Chapter 7 WAN screens NN47923 500 Figure 31 Dial Backup Setup ...
Страница 128: ...128 Chapter 7 WAN screens NN47923 500 ...
Страница 152: ...152 Chapter 9 Static Route screens NN47923 500 ...
Страница 194: ...194 Chapter 11 Firewall screens NN47923 500 ...
Страница 210: ...210 Chapter 13 VPN NN47923 500 Figure 67 Summary IP Policies ...
Страница 222: ...222 Chapter 13 VPN NN47923 500 Figure 71 VPN Branch Office rule setup ...
Страница 231: ...Chapter 13 VPN 231 Nortel Business Secure Router 252 Configuration Basics Figure 72 VPN Branch Office IP Policy ...
Страница 249: ...Chapter 13 VPN 249 Nortel Business Secure Router 252 Configuration Basics Figure 78 VPN Client Termination ...
Страница 256: ...256 Chapter 13 VPN NN47923 500 Figure 81 VPN Client Termination advanced ...
Страница 260: ...260 Chapter 13 VPN NN47923 500 ...
Страница 264: ...264 Chapter 14 Certificates NN47923 500 Figure 83 My Certificates ...
Страница 270: ...270 Chapter 14 Certificates NN47923 500 Figure 85 My Certificate create ...
Страница 274: ...274 Chapter 14 Certificates NN47923 500 Figure 86 My Certificate details ...
Страница 282: ...282 Chapter 14 Certificates NN47923 500 Figure 89 Trusted CA details ...
Страница 298: ...298 Chapter 14 Certificates NN47923 500 ...
Страница 316: ...316 Chapter 16 IEEE 802 1x NN47923 500 ...
Страница 320: ...320 Chapter 17 Authentication server NN47923 500 Figure 106 Local User database edit ...
Страница 328: ...328 Chapter 17 Authentication server NN47923 500 ...
Страница 376: ...376 Chapter 20 Logs Screens NN47923 500 Figure 150 Log settings ...
Страница 386: ...386 Chapter 20 Logs Screens NN47923 500 ...
Страница 392: ...392 Chapter 21 Call scheduling screens NN47923 500 Figure 157 Applying Schedule Sets to a remote node ...
Страница 393: ...Chapter 21 Call scheduling screens 393 Nortel Business Secure Router 252 Configuration Basics ...
Страница 394: ...394 Chapter 21 Call scheduling screens NN47923 500 ...
Страница 409: ...Chapter 22 Maintenance 409 Nortel Business Secure Router 252 Configuration Basics Figure 170 Restart screen ...
Страница 410: ...410 Chapter 22 Maintenance NN47923 500 ...
Страница 430: ...430 Appendix A Troubleshooting NN47923 500 ...