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Hình 13.2: mạng nội bộ này đã rò rỉ một số định tuyến, máy chủ thông báo các tuyến đường bên ngoài vào mạng nội bộ. Các phần trong dòng in đậm là đường dẫn đến "mạng nội bộ" các điểm đến đi qua internet, tức là, đang ở bên ngoài mạng nội bộ. Những rò rỉ không phải là rất phổ biến và dễ dàng để sửa chữa. | Intranet Routing Tricks 251 Figure 13.2 This intranet has several routing leaks hosts that announce external routes into the intranet. The sections in bold lines are paths to intranet destinations that traverse the internet i.e. are outside the intranet. These leaks are not very common and are generally easy to fix. 252 Network Layout Table 13.1 Some interesting intranet statistics. This data was summarized from authorized scans of a number of Lumeta customers networks. Measurement Number of IP addresses found on the intranet 7 936-364.171 Potential number of hosts defined by the list of known intranet CIDR blocks. Some companies allocate their space more frugally than others which can ease network management and future network mergers. 81 340-745 014 656 Percent of all the routers discovered on the intranet that responded to SNMP community string public. Most companies want this value to be 0 0.14 -78.57 Percent of all the routers discovered on the intranet that responded lo common SNMP community strings other than public. 0.00 -31.59 Number of hosts in the intranet that appear to have uncontrolled outbound access to the Internet. Some companies have policies prohibiting this 0-176 981 Number of hosts that accept UDP packets from the Internet host leaks. and also have access to the intranet. This violates nearly all corporate security policies. Such hosts are often home computers with tunnels to corporate intranets. They may also be running personal Web sites. Some have been gateways for hackers into corporate networks 0-5 867 Percent of hosts running Windows software. This is a rough statistic based on crude TTL fingerprinting. 36.45 -83.84 In Host We Trust 253 13.3 In Host We Trust We need firewalls when the hosts cannot protect themselves from attack. We also use them to provide an extra layer of protection around hosts and network regions that are supposed to be secure. Traditionally firewalls have been used to protect organizations from attacks from the .
