
166
Chapter 10 Firewalls
NN47922-500
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Restrict use of certain protocols, such as Telnet, to authorized users on the
LAN.
These custom rules work by evaluating the network traffic’s 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 167
), 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.
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 BSR222
Страница 28: ...28 Tables NN47922 500 ...
Страница 50: ...50 Chapter 2 Introducing the WebGUI NN47922 500 ...
Страница 66: ...66 Chapter 3 Wizard setup NN47922 500 ...
Страница 87: ...Chapter 5 System screens 87 Nortel Business Secure Router 222 Configuration Basics Figure 17 Time and Date ...
Страница 92: ...92 Chapter 5 System screens NN47922 500 ...
Страница 96: ...96 Chapter 6 LAN screens NN47922 500 Configuring IP Click LAN to open the IP screen Figure 19 LAN IP ...
Страница 104: ...104 Chapter 6 LAN screens NN47922 500 ...
Страница 115: ...Chapter 7 WAN screens 115 Nortel Business Secure Router 222 Configuration Basics Figure 27 WAN IP ...
Страница 123: ...Chapter 7 WAN screens 123 Nortel Business Secure Router 222 Configuration Basics Figure 32 Dial Backup Setup ...
Страница 154: ...154 Chapter 9 Static Route screens NN47922 500 ...
Страница 196: ...196 Chapter 11 Firewall screens NN47922 500 ...
Страница 212: ...212 Chapter 13 VPN NN47922 500 Figure 68 Summary IP Policies ...
Страница 223: ...Chapter 13 VPN 223 Nortel Business Secure Router 222 Configuration Basics Figure 72 VPN Branch Office rule setup ...
Страница 249: ...Chapter 13 VPN 249 Nortel Business Secure Router 222 Configuration Basics Figure 79 VPN Client Termination ...
Страница 256: ...256 Chapter 13 VPN NN47922 500 Figure 82 VPN Client Termination advanced ...
Страница 260: ...260 Chapter 13 VPN NN47922 500 ...
Страница 264: ...264 Chapter 14 Certificates NN47922 500 Figure 84 My Certificates ...
Страница 273: ...Chapter 14 Certificates 273 Nortel Business Secure Router 222 Configuration Basics Figure 87 My Certificate details ...
Страница 281: ...Chapter 14 Certificates 281 Nortel Business Secure Router 222 Configuration Basics Figure 90 Trusted CA details ...
Страница 290: ...290 Chapter 14 Certificates NN47922 500 Figure 95 Trusted remote host details ...
Страница 314: ...314 Chapter 16 IEEE 802 1x NN47922 500 ...
Страница 318: ...318 Chapter 17 Authentication server NN47922 500 Figure 107 Local User database edit ...
Страница 326: ...326 Chapter 17 Authentication server NN47922 500 ...
Страница 374: ...374 Chapter 20 Logs Screens NN47922 500 Figure 151 Log settings ...
Страница 384: ...384 Chapter 20 Logs Screens NN47922 500 ...
Страница 390: ...390 Chapter 21 Call scheduling screens NN47922 500 Figure 158 Applying Schedule Sets to a remote node ...
Страница 402: ...402 Chapter 22 Maintenance NN47922 500 Figure 170 Restart screen ...
Страница 422: ...422 Appendix A Troubleshooting NN47922 500 ...