tailieunhanh - Ebook Cisco security architectures: Phần 2

Part 1 of the book serial ebook Cisco security architectures to part 2 of you will continue to learn about relevant issues such as: Cisco router access lists, advanced cisco router security features, Non-IP access lists, the cisco PIX. | Chapter 7 Cisco Router Access Lists Overview In the previous chapters we have reviewed the operation of many protocols. As we will see an understanding of the inner workings of these protocols and their address structure is critical to the proper construction and implementation of Cisco access lists. In this chapter we will begin our discussion by defining Cisco access lists and examining their role in securing Cisco networks. We then examine the Cisco methodology for constructing and maintaining Cisco access lists. Once we have a basic understanding of how access lists are constructed we will begin our discussion of IP access lists and provide detailed examples showing their use. We will also make a distinction between traditional IP access lists and next-generation IP access lists. Next-generation IP access lists provide significant enhancements beyond the capability of traditional IP access lists. Cisco Access List Technology We will begin by discussing why access lists are important to Cisco security. There are many facets to security and one of the most important is the capability to control the flow of data packets within a network. Specifically preventing packets from entering a network by examining information within the packet header is critical. This capability is typically termed packet filtering and is one of the most important uses of Cisco access lists although as we shall see it is not the only use. Packet filtering allows you to control data flows in your network based on source and destination IP addresses and the type of application used. For example packet filtering allows you to prevent packets from entering your network if the packets are part of a telnet session that originated from certain address ranges. Additionally you can prevent all packets from a certain IP address range from entering your network regardless of the application used. These kinds of functions are especially useful when applied to routers. In many cases routers serve as a

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