Icnd210 s06l01

Editor's Notes

• #3: <number> Layer 2 of 2 Emphasize: An access list is a mechanism for identifying particular traffic. One application of an access list is for filtering traffic into or out of a router interface.
• #4: <number> Purpose: This figure illustrates common uses for IP access lists. Emphasize: While this chapter focuses on IP access lists, the concept of access lists as mechanisms to control traffic in a network applies to all protocols. Note: An improved security solution is the lock-and-key access feature, which is available only with IP extended access lists. Lock-and-key access allows you to set up dynamic access lists that grant access per user to a specific source/destination host through a user authentication process. You can allow user access through a firewall dynamically, without compromising security restrictions. Transition: The following figure is the first of a three-layer build that presents other uses of access lists specific to Cisco IOS™ features.
• #5: <number> Layer 3 of 3 Purpose: This figure is the last layer of the build for other uses of access lists. Emphasize: Access lists are used to define input traffic for route filtering to restrict the contents of routing updates. Transition: The following figure is a two-layer build to show the difference between inbound and outbound access lists.
• #6: <number> Layer 3 of 3 Purpose: Shows a deny result of the access list test. Emphasize: Now the packet is discarded into the packet discard bucket. The unwanted packet has been denied access to the outbound interface. The Notify Sender message shows a process like ICMP, returning an “administratively prohibited” message back to the sender.
• #7: <number> Layer 4 of 4 Purpose: Shows the implicit “deny all.” Emphasize: Describe the final access list test to match any packets not covered by earlier access list statements. All remaining packets match the “Implicit Deny” and are discarded into the bit bucket.
• #8: <number> Layer 3 of 3 Purpose: Describe an inbound versus outbound access list on an interface.
• #9: <number> Layer 3 of 3 Emphasize: Layer 3—Adds the Novell IPX access lists covered in Chapter 11, “Configuring Novell IPX,” and the number ranges for these types of access lists. As of Release 11.2.4(F), IPX also supports named access lists. Point out that number ranges generally allow 100 different access lists per type of protocol. When a given hundred-number range designates a standard access list, the rule is that the next hundred-number range is for extended access lists for that protocol. Exceptions to the numbering classification scheme include AppleTalk and DECnet, where the same number range can identify various access list types. For the most part, number ranges do not overlap between different protocols. Note: With Cisco IOS 12.0, the IP access-lists range has been expanded to also include: <1300-1999> IP standard access list (expanded range) <2000-2699> IP extended access list (expanded range)
• #10: <number>
• #11: <number>
• #12: <number>
• #13: <number>
• #14: <number>
• #15: <number> Purpose: This graphic describes the binary wildcard masking process. Emphasize: Introduce the wildcard bit process. Tell students that the wildcard bit matching process is different than the IP subnet addressing mask covered earlier. Illustrate how wildcard masking works using the examples shown in the graphic table. The term wildcard masking is a nickname for this access list mask-bit-matching process. This nickname comes from an analogy of a wildcard that matches any other card in a poker game. Emphasize the contrast between wildcard masks and subnet masks, stated in the Student Guide note. The confusion over wildcard and subnet masks can be a key obstacle to learning if students fail to understand the different uses of binary 0 and binary 1 in the two mask types. Point out that the 1 bits in a wildcard mask need not be contiguous, while the 1 bits in a subnet mask need to be contiguous. Wildcard is like the DOS “*” character.
• #16: <number> Purpose: This slide describes an example of how wildcard mask bits will match all hosts on subnets 172.30.16.0/24 to 172.30.31.0/24. Emphasize: This process requires a thorough understanding of binary numbering, what values to use in the power of two bit positions, and how to convert a number from decimal to binary. If some of your students seem to lack this understanding, tell them that responsibility for complex access list design is an advanced configuration skill. Later, this course offers a hands-on lab to allow practice designing simple access lists. If you feel that your students need another example to improve their understanding of the process, prepare another example as a chalk talk. Consider having students volunteer to help as you solve your own example that lines up the binary bits of the address and the binary bits of the wildcard mask.
• #17: <number> Purpose: This graphic shows students how to use the host abbreviation in the extended access list wildcard mask. Emphasize: This abbreviation means check the bit value in all bit positions, which has the effect of matching only the specified IP host address in all bit positions.