Chapter 22 Advanced DHCP Server Properties

Using Extensions to Affect DHCP Server Behavior

You can solve the problem of the two IP addresses by writing either of these extensions:

•One that causes the DHCP server to drop the Token Ring (6) hardware type packet.

•One that changes the Token Ring packet to an Internet packet and then switches it back again on exit. Although this extension would be more complex, the DHCP client could thereby use either return from the DHCP server.

You can write extensions in TCL or C/C++:

•TCL—Makes it a bit easier and quicker to write an extension. If the extension is short, the interpreted nature of TCL does not have a serious effect on performance. When you write an extension in TCL, you are less likely to introduce a bug that can crash the server.

•C/C++—Provides the maximum possible performance and flexibility, including communicating with external processes. However, the complexity of the C/C++ API is greater and the possibility of a bug in the extension crashing the server is more likely than with TCL.

You create extensions at specific extension points. Extension points include three types of dictionaries—request, response, and environment. One or more of these dictionaries are available for each of the following extension points:

1.init-entry—Extension point that the DHCP server calls when it configures or unconfigures the extension. This occurs when starting, stopping, or reloading the server. This entry point has the same signature as the others for the extension. Dictionaries: environment only.

2.post-packet-decode—Rewrites the input packet. Dictionaries: request and environment.

3.post-class-lookup—Evaluates the result of a client-class-lookup-idoperation on the client-class. Dictionaries: request and environment.

4.pre-client-lookup—Affects the client being looked up, possibly by preventing the lookup or supplying data that overrides the existing data. Dictionaries: request and environment.

5.post-client-lookup—Reviews the operation of the client-class lookup process, such as examining the internal server data structures filled in from the client-class processing. You can also use it to change any data before the DHCP server does additional processing. Dictionaries: request and environment.

6.check-lease-acceptable—Changes the results of the lease acceptability test. Do this only with extreme care. Dictionaries: request, response, and environment.

7.lease-state-change—Determines when the lease state changes this only with extreme care. Dictionaries: response and environment.

8.pre-packet-encode—Changes the data sent back to the DHCP client in the response, or change the address to which to send the DHCP response. Dictionaries: request, response, and environment.

9.pre-dns-add-forward—Alters the name used for the DNS forward (A record) request. Dictionaries: environment only.

10.post-send-packet—Used after sending a packet for processing that you want to perform outside of the serious time constraints of the DHCP request-response cycle. Dictionaries: request, response, and environment.

To extend the DHCP server, do the following:

Step 1 Write the extension in Tcl, C or C++ and install it in the server extensions directory, on:

•UNIX:

–Tcl—/opt/nwreg2/extensions/DHCP/tcl

–C or C++—/opt/nwreg2/extensions/DHCP/dex

Cisco CNS Network Registrar User’s Guide

 

OL-6240-02

22-9

 

 

 

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Cisco Systems OL-6240-02 manual Unix, 22-9
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OL-6240-02 specifications

Cisco Systems OL-6240-02 is a highly regarded certification exam that delves into the realm of enterprise networking, particularly focusing on the Cisco Certified Network Professional (CCNP) Routing and Switching track. This particular exam serves as a critical test for network professionals aiming to validate their skills and knowledge in advanced routing technologies and network design.

One of the main features of OL-6240-02 is its emphasis on in-depth understanding of IP routing principles. Candidates are expected to demonstrate proficiency in configuring, maintaining, and troubleshooting complex routing protocols like OSPF (Open Shortest Path First), EIGRP (Enhanced Interior Gateway Routing Protocol), and BGP (Border Gateway Protocol). This includes comprehending routing algorithms, path selection, and the implementation of route redistribution, which are essential for optimizing network performance.

The exam also covers the characteristics of network security and infrastructure, where candidates must exhibit knowledge of implementing security protocols and best practices to safeguard network communications. This includes configuring virtual private networks (VPNs), utilizing access control lists (ACLs), and applying encryption techniques to secure data in transit.

Another crucial technology tested in OL-6240-02 is Quality of Service (QoS). Professionals must be adept at configuring QoS mechanisms to prioritize traffic, ensuring that critical applications receive the necessary bandwidth and latency requirements. This is increasingly important as businesses rely on a multitude of applications that have varying performance needs.

Cisco's emphasis on network automation and programmability is also a focal point of this certification. Candidates are expected to be familiar with using Cisco's software-defined networking (SDN) solutions and automation tools, which are essential for modern network management. This involves understanding how to leverage APIs and modeling tools to streamline network operations and enhance efficiency.

To succeed in OL-6240-02, candidates should possess a solid foundation in network fundamentals and have hands-on experience with Cisco devices. The certification not only validates expertise but also prepares professionals for real-world challenges in designing, implementing, and troubleshooting enterprise networks. Overall, OL-6240-02 is a stepping stone for network professionals seeking higher-level certifications and career advancements in the ever-evolving field of networking.
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