Learning Simple NAT

NAT(Network Address Translation) is the most basic and important technique used almost everywhere wherein you want 'n' number of clients on your LAN gain access to internet with just holding on to one public IP address. A very brief and nice persentation I found on Cisco Blog. Hope it will be useful

in reference to:

"Learning Simple NAT"
- Cisco Blog: Learning Simple NAT (view on Google Sidewiki)

Explanation of port forwarding and reverse tunnel

A nice article. Run through the wizard explanation on the left navigation to know more

in reference to: Article about port forwarding and reverse tunnel (view on Google Sidewiki)

DHCP Option 60 Use

The DHCP functionality supports the DHCP vendor class identifier option (option 60). This support allows DHCP relay to compare option 60 strings in received DHCP client packets against strings that you configure on the router. You can use the DHCP relay option 60 feature when providing converged services in your network environment—option 60 support enables DHCP relay to direct client traffic to the specific DHCP server that provides the service that the client requires. Or, as another option, you can configure option 60 strings to direct traffic to the DHCP local server in the current virtual router.

For example, you might have an environment in which some DHCP clients require only Internet access, while other clients require IPTV service. The clients that need Internet access get their addresses assigned by the DHCP local server on the E-series router (in equal-access mode). Clients requiring IPTV must be relayed to a specific DHCP server that provides the service. To support both types of clients, you configure two option 60 strings on the DHCP relay. Now, when any DHCP client packets are received with option 60 strings configured, the strings are matched against all strings configured on the DHCP relay. If the client string matches the first string you configured, that client is directed to the DHCP local server and gains Internet access. Client traffic with an option 60 string that matches your second string is relayed to the DHCP server that provides the IPTV service. In addition, you can configure a default action, which DHCP relay performs when a client option 60 string does not match any strings you have configured—for example, you might specify that all clients with non-matching strings be dropped.

in reference to: Using Option 60 Strings to Forward Client Traffic to Specific DHCP Servers (view on Google Sidewiki)

Change the Maximum Transmission Unit (MTU) Size in Windows XP

To Change the Maximum Transmission Unit (MTU) Size in Windows XP. Follow this link: http://www.pctools.com/guides/registry/detail/280/

in reference to:

"Change the Maximum Transmission Unit (MTU) Size"
- Change the Maximum Transmission Unit (MTU) Size at Registry Guide for Windows (view on Google Sidewiki)

TCP/IP Protocol Formats

For Quick reference to TCP/IP header formats visit http://www.sans.org/resources/tcpip.pdf

For Our Network Testers

This one is for our dear network testers who are into testing of network devices. Do use following books as reference:

• Network performance open source toolkit by Richard Blum
• The art of testing network systems

Difference between Good Tester and Good Developer

Good Testers	Good Developers
Get up to speed quickly	Thorough understanding
Domain knowledge	Knowledge of product internals
Ignorance is important	Expertise is important
Focus on what can go wrong	Focus on how it can work
Comfortable with conflict	Avoid conflict
Report problems	Understand problems

Software Testing Life Cycle

Software testing life cycle identifies what test activities to carry out and when (what is the best time) to accomplish those test activities. Even though testing differs between organizations, there is a testing life cycle.

Software Testing Life Cycle consists of six (generic) phases:

* Test Planning,
* Test Analysis,
* Test Design,
* Construction and verification,
* Testing Cycles,
* Final Testing and Implementation and
* Post Implementation.

Software testing has its own life cycle that intersects with every stage of the SDLC. The basic requirements in software testing life cycle is to control/deal with software testing – Manual, Automated and Performance.

Test Planning

This is the phase where Project Manager has to decide what things need to be tested, do I have the appropriate budget etc. Naturally proper planning at this stage would greatly reduce the risk of low quality software. This planning will be an ongoing process with no end point.

Activities at this stage would include preparation of high level test plan-(according to IEEE test plan template The Software Test Plan (STP) is designed to prescribe the scope, approach, resources, and schedule of all testing activities. The plan must identify the items to be tested, the features to be tested, the types of testing to be performed, the personnel responsible for testing, the resources and schedule required to complete testing, and the risks associated with the plan.). Almost all of the activities done during this stage are included in this software test plan and revolve around a test plan.

Test Analysis

Once test plan is made and decided upon, next step is to delve little more into the project and decide what types of testing should be carried out at different stages of SDLC, do we need or plan to automate, if yes then when the appropriate time to automate is, what type of specific documentation I need for testing.

Proper and regular meetings should be held between testing teams, project managers, development teams, Business Analysts to check the progress of things which will give a fair idea of the movement of the project and ensure the completeness of the test plan created in the planning phase, which will further help in enhancing the right testing strategy created earlier. We will start creating test case formats and test cases itself. In this stage we need to develop Functional validation matrix based on Business Requirements to ensure that all system requirements are covered by one or more test cases, identify which test cases to automate, begin review of documentation, i.e. Functional Design, Business Requirements, Product Specifications, Product Externals etc. We also have to define areas for Stress and Performance testing.

Test Design

Test plans and cases which were developed in the analysis phase are revised. Functional validation matrix is also revised and finalized. In this stage risk assessment criteria is developed. If you have thought of automation then you have to select which test cases to automate and begin writing scripts for them. Test data is prepared. Standards for unit testing and pass / fail criteria are defined here. Schedule for testing is revised (if necessary) & finalized and test environment is prepared.

Construction and verification

In this phase we have to complete all the test plans, test cases, complete the scripting of the automated test cases, Stress and Performance testing plans needs to be completed. We have to support the development team in their unit testing phase. And obviously bug reporting would be done as when the bugs are found. Integration tests are performed and errors (if any) are reported.

Testing Cycles

In this phase we have to complete testing cycles until test cases are executed without errors or a predefined condition is reached. Run test cases --> Report Bugs --> revise test cases (if needed) --> add new test cases (if needed) --> bug fixing --> retesting (test cycle 2, test cycle 3….).

Final Testing and Implementation

In this we have to execute remaining stress and performance test cases, documentation for testing is completed / updated, provide and complete different matrices for testing. Acceptance, load and recovery testing will also be conducted and the application needs to be verified under production conditions.

Post Implementation

In this phase, the testing process is evaluated and lessons learnt from that testing process are documented. Line of attack to prevent similar problems in future projects is identified. Create plans to improve the processes. The recording of new errors and enhancements is an ongoing process. Cleaning up of test environment is done and test machines are restored to base lines in this stage.

Software Testing Life Cycle

Planning Phase
Activities: Create high level test plan
Outcome: Test plan, Refined Specification

Analysis Phase
Activities: Create detailed test plan, Functional Validation Matrix, test cases
Outcome: Revised Test Plan, Functional validation matrix, test cases

Design Phase
Activities: test cases are revised; select which test cases to automate
Outcome: evised test cases, test data sets, sets, risk assessment sheet

Construction Phase
Activities: scripting of test cases to automate,
Outcome: test procedures/Scripts, Drivers, test results, Bugreports.

Testing cycles Phase
Activities: complete testing cycles
Outcome: Test results, Bug Reports

Final testing Phase
Activities: execute remaining stress and performance tests, complete documentation
Outcome: Test results and different metrics on test efforts

Post implementation Phase
Activities: Evaluate testing processes
Outcome: Plan for improvement of testing process

Control & Data Plane in networking

Routers (also known as layer-3 switches) perform two basic functions:

• Forward packets between interfaces (layer-3 switching).
• Exchange reachability information between routers (routing).

There is no conceptual difference between a router and a layer-3 switch. Layer-3 switching is a product of creative vendor marketing.

Switching (packet forwarding) is performed in the data (forwarding) plane. Routing (exchange of routing information) is performed in the control plane. The information collected with routing protocols (for example, ) is used to build topology databases (also known as link state databases or routing databases depending on the terminology of the routing protocol). The routing protocols extract best paths from the protocol-specific data structures and insert them in the routing table. The routing table might contain recursive information and is thus not suitable for fast packet forwarding. The routers use two mechanisms to speed up packet forwarding:

• They can cache the results of routing table lookup for recently used destinations (fast switching in Cisco IOS terminology).
• They can pre-compute the actual forwarding data for every destination and store them in the forwarding table that can be directly used by the data plane.

Figure 1 illustrates the relationships between the control and the data planes.

Figure 1: Control and data planes

Processing of inbound packets

In most router implementations, the data plane receives and processes all inbound packets and selective forwards packets destined for the router (for example, routing protocol updates) or packets that need special processing (for example, IP datagrams with IP options or IP datagrams that have exceeded their TTL) to the control plane.

The control plane might pass outbound packets to the data plane or use its own forwarding mechanisms to determine the outgoing interface and the next-hop router (for example, when using the local policy routing).

Figure 2 shows typical packet flow in a router.

Figure 2: Typical packet flow

Common architectures

In devices with distributed (multiple CPU) architecture, the central CPU implements the control plane (most routing protocols are designed to operate on a single control plane node), while the CPUs on linecards implement distributed high-speed data plane.

High-speed layer-3 switches commonly implement data plane with special hardware (for example, Ternary Content Addressable Memory; TCAM).

Single-CPU devices that perform layer-3 switching in software usually implement the data plane in the interrupt code (high-priority process-independent code in the kernel of the operating system) to minimize the overhead associated with forwarding of individual packet. For example, Cisco IOS implements the Cisco Express Forwarding (CEF) and the fast switching in the interrupt code.

Tackling With Endianess

Writing endian-independent code in C  

Architectures, processors, network stacks, and communication protocols all have to define endianness at some point. This article explains how endianness affects code, how to determine endianness at run time, and how to write code that can reverse byte order and free you from being bound to a certain endian.

Learn more:
Tackling Endianness 

VIM Editor Cheat Sheet

We all use VIM editor and we love it, but most of us don't know there are lots of cheat commands which are really useful. Do explore the VIM world and enjoy editing
Visual mode allows several commands to be run in conjuction with it. To use it type 'v' then move the cursor, this will create a highlighted block of text. In the windows version of gvim, you can use the mouse to select blocks of text. I prefer to use 'V' which is line based visual mode.

Here are some commands commonly used with visual mode.

• > shift the block right one shiftwidth
• <>
• = reindent the block
• y yank ( copy ) the block ( paste with a p )
• d delete the block
• c change the block

Porting Software

In the near future, I may work on a project which requires porting skills. So while searching for a book in that area, I came across this one "Porting UNIX Software" from O'reilly.

Top 25 Programming Errors by NSA

by M. E. Kabay on 2/12/09

The National Security Agency, working with MITRE Corp., SANS, and dozens of industry experts from many other organizations, has published a valuable list of the top 25 most dangerous programming errors. A must-read for professionals, educators and students.

The Basics of Using LinkedIn to Find a Job

via The LinkedIn Blog by Adam Nash on 2/3/09

There was a great post yesterday on Guy Kawasaki's blog on 10 ways to find a job using LinkedIn.

It's a very timely post because I find that, even among my fairly young and tech-savvy friends, people still have trouble imagining how to best leverage their professional network online to help them with their job search. Too often, people think of social networks as just an online Rolodex or messaging client. They don't realize that while there is great advantage in keeping up with your connections, the true transformative power is the ability to look past the people you know directly to explore options in your broader network.

Here is a quote from the article:

Searching for a job can suck if you constrain yourself to the typical tools such as online jobs boards, trade publications, CraigsList, and networking with only your close friends. In these kinds of times, you need to use all the weapons that you can, and one that many people don't—or at least don't use to the fullest extent, is LinkedIn.

I won't paraphrase the entire article here - it's worth reading directly. But it is worth noting the three steps that I highly recommend, regardless of whether you are looking for a job or not:

• Be found. It's almost criminal to leave your LinkedIn profile unfinished. Think of it as search optimization, but not for a website - for you. The more positions you list, education you cite, and skills you highlight, the more likely it is that the right people will find you. It's not hard - in fact, if you have a resume handy from your last job search, you can fill in a profile typically with a few minutes of cut & paste. Most people are shocked to find out how many great opportunities find them once they fill out their professional profile.

Build your LinkedIn Profile

• Bring your network online. Your network is one of your most valuable assets, but it does little good for you offline. Upload your Address Book, invite the people you want to connect with, and get connected. Most people don't realize that having your network online means that you can now use it as a personalized search engine for both who and what you know. That's exactly you only want to connect with people you actually know. It's no good finding out you are one degree away from the company of your dreams, if that connection doesn't know you from Adam (pardon the expression). Worse, that false connection can even "crowd out" a real connection to that company in the LinkedIn search engine. Your relationships are the heart of social relevance - use them.

Build your Online Professional Network on LinkedIn

• Search! You'd think that after a decade of search engines people would get this, but it's amazing to watch the light go on once they search for something other than a name. Interested in working for clean tech? Try searching for it. Search the company directory on LinkedIn. Find companies in your favorite industry, in your favorite city. Then search your network ("People Search") for that company name. If you've done steps 1 & 2, you'll be pleasantly surprised at what a small world it is. If you are looking for a job, and you aren't spending hours a day on LinkedIn, chances are it's because you haven't discovered the power of people search.

Search for people, companies or jobs on LinkedIn

LinkedIn, of course, has a complete Jobs section to help you actually search for posted openings.

Hope this helps people out there who want to get started. We're all hoping that LinkedIn can be a real force for good in 2009, helping people find the right opportunity in a tough job market.

TACACS+ and RADIUS Comparison

Following link will take you to differences between most widely used security protocols RADIUS and TACACS+

http://www.cisco.com/en/US/tech/tk59/technologies_tech_note09186a0080094e99.shtml#comp_udp_tcp

Writing Network Device Drivers for Linux

via Linux Gazette on 11/1/08

This article has been written for kernel newcomers interested in learning about network device drivers. It assumes that reader has a significant exposure to C and the Linux environment.