
Chapter 10 Firewalls
167
Nortel Business Secure Router 222 Configuration — Basics
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).
UDP/ICMP security
UDP and ICMP do not contain any connection information (such as sequence
numbers). However, at the very minimum, they contain an IP address pair (source
and destination). UDP also contains port pairs, and ICMP has type and code
information. All of this data can be analyzed in order to build virtual connections
in the cache.
For instance, any UDP packet that originates on the LAN creates a cache entry. Its
IP address and port pairs are stored. For a short period of time, UDP packets from
the WAN that have matching IP and UDP information are allowed back in through
the firewall.
A similar situation exists for ICMP, except that the Business Secure Router is
even more restrictive. Specifically, only outgoing echoes allow incoming echo
replies, outgoing address mask requests allow incoming address mask replies, and
outgoing timestamp requests allow incoming timestamp replies. No other ICMP
packets are allowed in through the firewall, simply because they are too
dangerous and contain too little tracking information. For instance, ICMP redirect
packets are never allowed in, since they can be used to reroute traffic through
attacking machines.
Upper layer protocols
Some higher layer protocols (such as FTP and RealAudio) utilize multiple
network connections simultaneously. In general terms, they usually have a control
connection, which is used for sending commands between endpoints, and then
data connections, which are used for transmitting bulk information.
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 ...