Archive for January, 2012

Default STP Behavior on Cisco Switches

Tuesday, January 31st, 2012

In a prior blog, Functionality of Layer 2 Switches/Bridges, I discussed the core functionality of layer 2 switches. In this blog, I hit upon the Spanning Tree Protocol (STP) used on layer 2 switches to prevent loops. As mentioned before, loops can be created via layer 2 switches by using more than one link to connect to the same switches. This is often done for redundancy purposes but is not possible without STP. (more…)

Twitt

The Rise of the Hybrid Cloud

Sunday, January 15th, 2012

Hybrid CloudAs many organizations move their corporate services to private clouds to cut costs, enable rapid provisioning of resources, enable advanced monitoring, and increase up-time, I believe we will see a continuous uptake of solutions which tie private cloud services and public cloud services together into something called the “hybrid cloud”. The key will be to use a secure connection such as a VPN tunnel to connect the private and public clouds together. This can be a great cost-effective solution as a company, especially a start-up, doesn’t have to carry the burden of building the entire infrastructure from scratch. (more…)

Twitt

How to Transfer Your Putty Settings Between PCs Running Windows

Sunday, January 8th, 2012

I can’t tell you how many times I’ve had people ask me how they can export their Putty settings. For those of you who have been completely in the dark for the last decade, Putty is a Telnet and SSH client for Windows and Unix. Below I outline the steps to accomplish this goal; these steps should work for all versions of Windows. (more…)

Twitt

Cisco – Filtering Unwanted Packets with Standard Access Lists

Saturday, January 7th, 2012

Access lists (ACLs) are basically statements that packets are compared against for the purpose of taking some action if a match occurs. After an access list is created, it can be applied to inbound or outbound traffic; in some cases it is applied in both directions. You can think of an ACL as a method for filtering packets that meet a specific criteria so further action can be taken on them. (more…)

Twitt

Perl – Changing the Input Line Separator and Using the “chomp” Function

Friday, January 6th, 2012

In this blog I demonstrate how you can change the input line separator in Perl and use Perl’s “chomp” function. Note, the input line separator is operating system dependent; see the following prior blog of mine where I discuss this subject in more detail: Unix shell script – convert Mac ASCII file to Unix ASCII file. The “chomp” function checks to see if the last character of a string or list of strings matches the line separator character stored in the ‘$/’ system variable; if there is a match, the character is deleted. (more…)

Twitt

Perl – Uppercase to Lowercase Conversion via the Translation Operator

Wednesday, January 4th, 2012

Perl’s translation operator provides a way to substitute one group of characters for another. In the below script I demonstrate how easy it is to use the translation operator to convert standard input from the command prompt from uppercase letters to lowercase. You can also use Perl’s lc() function to accomplish the same thing more easily. (more…)

Twitt

OSPF Explained and Useful Troubleshooting Commands

Wednesday, January 4th, 2012

Open Shortest Path First (OSPF) is an open standard link-state routing protocol that supports multiple equal-cost routes to the same destination (four by default). OSPF constructs a shortest path tree and then updates the routing table with the best paths. In this blog I I will be explaining OSPF in the context of OSPF on Cisco routers, so I will be using Cisco IOS command syntax. For some of the commands I have included screenshots from a Cisco 2621XM [IOS 12.3(16a)] router. (more…)

Twitt