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. Continue reading
OSPF Explained and Useful Troubleshooting Commands
Posted in Cisco, Labs, Networking, Protocols, Technology, Troubleshooting
Tagged ABRs, adjacency, area 0, Area Border Routers, AS, ASBR, Autonomous System, Autonomous System Border Router, backbone area, Backup Designated Router, BDR, Cisco, Cisco 2126XM, Cisco 2126XM router, Cisco IOS, cisco router, cost, Designated Router, Hello packets, Link State Advertisement, LSA, neighbor, Neighbors, Open Shortest Path First, OSPF, OSPF Adjacencies, OSPF area, OSPF Backup Designated Router, OSPF BDR, ospf cost, ospf database, OSPF Designated Router, OSPF Hello Packets, ospf neighbor, OSPF Neighbors, OSPF process, OSPF Router ID, ospf troubleshooting, router, Router ID, Shortest Path First, shortest path tree, SPF
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Perl – Using Pattern-sequence Memory with Regular Expressions
Pattern-sequence memory is very useful when you want to match the same character in several places but don’t care which character you match as long as all occurrences are the same character. For example, the below code matches the date format “dd-mm-yy” where the dashes can be any two of the same non-word characters (in regex notation the range would be [^_0-9a-zA-Z]). Pattern sequences are stored in memory from left to right, so “\1” would represent the first match. Continue reading
Posted in Perl, Programming Languages, Technology
Tagged pattern memory, pattern-sequence, pattern-sequence memory, Pattern-sequence Memory with Regular Expressions, perl, perl regular expressions, regex, regular expressions, sequence memory, Using Pattern-sequence Memory with Regular Expressions
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Setting-up DHCP with IP Helper-Address on Cisco Routers
In a prior lab, Setting-up DHCP on Cisco Routers, I discussed how to setup a Cisco router as a DHCP server. In this lab, I use a DHCP server setup on one subnet to provide DHCP services to two different subnets. For this lab I use a Cisco 2126XM router [IOS Version 12.2(28)] as the layer 3 device and two Cisco WS-C2950-24 switches [IOS Version 12.1(22)EA4X] as the layer 2 devices. The network diagram and DHCP server configuration for this lab is shown below. Continue reading
Posted in Cisco, Labs, Networking, Protocols, Technology
Tagged Cisco, Cisco 2126XM, Cisco 2126XM router, Cisco WS-C2950-24, Cisco WS-C2950-24 switch, configure DHCP, dhcp, DHCP broadcasts, dhcp configuration, Dynamic Host Configuration Protocol, ip helper, ip helper-address, Setting-up DHCP with IP Helper-Address on Cisco Routers
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HumairAhmed.com: Top 500,000 Websites in US – Not Bad for a Blog!
Well, it looks like I’ve finally broken into the top 500,000 websites in the US in terms of traffic according to Alexa. Not bad for a semi-periodically updated blog I suppose. Most sites, especially personal blogs, don’t even make the ranking let alone break the 1,000,000 barrier. My global ranking is still around 4,000,000 to 5,000,000, which is still good for a blog. Continue reading
Posted in Blogging, Business, Humair's News Releases, Internet Search, News, Technology, Technology, Websites
Tagged ahmed, alexa, blog, blog rank, blogging, humair, Humair Ahmed, Humair Ahmed's blog, Humair's blog, site, site rank, website, website rank
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Setting-up DHCP on Cisco Routers
The Dynamic Host Configuration Protocol (DHCP) provides the capability to automatically allocate reusable network addresses and configuration options to hosts. Continue reading
Posted in Cisco, Labs, Networking, Protocols, Technology
Tagged BOOTP, Cisco, Cisco 2126XM, Cisco 2126XM router, cisco dhcp configuration, cisco router, cisco setup dhcp, Cisco switch, Cisco WS-C2960-24TT, Cisco WS-C2960-24TT switch, dhcp, dhcp configuration, Dynamic Host Configuration Protocol, router, switch
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Perl – Obtain the File Size
Here is a cool one line Perl script you can use to quickly obtain the file size of a file. The syntax to run the script is “perl [scriptname] [filename]”; in the below example I use the script itself as the file. Continue reading
Posted in Perl, Programming Languages, Technology
Tagged -s, file size, file size operator, get file size, perl, perl file size operator, perl get file size
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Perl – Writing the Linux ‘cat’ Utility
The below Perl code will give you similar results compared to the Linux ‘cat’ utility. At the command prompt, just enter “perl [scriptname] [filename1] [filename2] etc … Continue reading
Perl – File-Test Operators
In Perl, file-test operators are useful for determining the status of a file. Some of the operators below refer to the “real user” which is the User ID specified at login rather than “effectve User ID” which refers to the User ID you are currently working under. The general syntax is -[file-test operator] [operand being tested]. Continue reading
W3C Feed Validation Service and Markup Validation Service
The W3C Feed Validation Service is a very useful tool to validate the syntax of Atom or RSS feeds. I just used it to determine why my LinkedIn WordPress application could no longer connect to my WordPress RSS feed. Continue reading
Posted in CSS, HTML, Technology, Web Development, WordPress
Tagged Atom, Atom feed, CSS, CSS Validator, Feed Validation, Feed Validation Service, Link Checker, LinkedIn, LinkedIn WordPress application, LinkedIn WordPress application not working, LinkedIn WordPress blog, LinkedIn WordPress blog not working, LinkedIn WordPress issue, LinkedIn WordPress issues, LinkedIn WordPress problem, LinkedIn WordPress problems, Markup Validation, Markup Validation Service, RSS, RSS feed, W3C, W3C CSS Validator, W3C Feed Validation Service, W3C Link Checker, W3C Markup Validation Service, WordPress
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University of Berkeley Astronomers Discover Largest Known Black Holes
University of California, Berkeley Astronomers have discovered the largest black holes known to date. The black holes are estimated to be have masses equivalent to about 10 billion suns each (one black hole being slightly bigger than the other). The two black holes are in clusters of elliptical galaxies greater than 300 million light years away (1 light year is approximately 5.8 trillion miles). Continue reading
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