February 2nd, 2012
I discussed Enhanced Interior Gateway Routing Protocol (EIGRP) briefly in a prior blog, Load Balancing with EIGRP, however, in this lab I use two Cisco 3725 routers [IOS 12.4(15)T10] to demonstrate how to configure EIGRP; additionally, I’ll discuss some useful troubleshooting commands. Remember EIGRP is a Cisco proprietary routing protocol which allows for load balancing over equal and unequal links. When EIGRP is enabled, the router attempts to discover neighbors on interfaces by sending multicast EIGRP Hello messages via multicast address 224.0.0.10. The router then advertises to other neighbors about the subnets connected to its respective interfaces. Below is a diagram of the lab setup I will be using. Read the rest of this entry »
Tags: Cisco, Cisco 3725, Cisco 3725 router, Cisco 3725 routers, dynamic routing, EIGRP, Enhanced Interior Gateway Routing Protocol, router
Posted in Cisco, Labs, Networking, Protocols, Technology, Troubleshooting | No Comments »
February 1st, 2012
Per VLAN Spanning Tree Plus (PVST+) is a flavor of Spanning Tree Protocol (see prior blog, Default STP Behavior on Cisco Switches) which maintains a spanning tree instance for each VLAN in the network. This means certain VLAN trunks (using 802.1q) can be forwarded for some VLANs while being blocked for others. Further, changes in one STP domain will not effect other spanning tree instances on other VLANs. Additionally, since each VLAN is treated as a separate network, layer 2 load balancing can be accomplished by forwarding some VLANs on one trunk and other VLANs on another trunk. Read the rest of this entry »
Tags: avoid loop, Cisco, Cisco 3560, Cisco 3560 switch, Cisco switch, dot1q, loop, Per VLAN Spanning Tree Plus, prevent loop, PVST+, Spanning Tree Protocol, STP, switch, vlan
Posted in Cisco, Labs, Networking, Protocols, Technology | No Comments »
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. Read the rest of this entry »
Tags: Blocking, BPDUs, bridge ID, Bridge Protocol Data Units, broadcast storm, change root bridge, Cisco, Cisco 3560, designated port, device priority, Disabled, Forwarding, layer 2, layer 2 loop, Learning, Listening, loop, MAC address, prevent layer 2 loop, prevent loop, redundancy, root bridge, root port, Spanning Tree Protocol, STP
Posted in Cisco, Labs, Networking, Protocols, Technology | 1 Comment »
January 15th, 2012
As 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. Read the rest of this entry »
Tags: Amazon S3, Amazon Simple Storage Service, American cloud companie, avoid US cloud, avoid US-based cloud, cloud, controversial Patriot Act, hybrid cloud, Jon Stokes, non-US cloud provider, Patriot Act, PATRIOT Act Gives Foreigners Good Reason to Avoid US Cloud, private cloud, public cloud, unconstitutional Patriot Act, United States Patriot Act, VPN
Posted in Business, Technology, Technology, Virtualization and Cloud Computing | No Comments »
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. Read the rest of this entry »
Tags: export putty, export putty settings, export windows putty, export windows putty settings, hack, putty, putty hack, putty hack to export settings, putty windows registry hack, regedit, registry hack, Simon Tathamm, ssh client, telnet client, transfer putty settings, transfer putty settings between computers, transfer putty settings between pcs, windows, Windows 7, windows 7 registry hack, windows regedit, windows registry, windows registry hack
Posted in Applications, Hacks, Networking, Operating Systems, Technology, Tips & Tricks, Windows, Windows 7, Windows Server 2008 R2 | No Comments »
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. Read the rest of this entry »
Tags: access list, access lists, acess-lists, ACL, ACLs, block host, block ip address, block packet, block traffic, Cisco, Cisco 2611, Cisco 2611 router, deny host, deny ip address, deny packet, deny traffic, extended access list, filter, filter host, filter ip address, filter packet, filter traffic, named access list, router, standard access list, standard access-lists
Posted in Cisco, Labs, Networking | No Comments »
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. Read the rest of this entry »
Tags: $/, $/ system variable, change the input line separator, chomp, chomp function, input line separator, input line separator system variable, input line separator variable, perl, perl input line separator system variable, perl input line separator variable, remove newline, remove newline character
Posted in Perl, Programming Languages, Technology | No Comments »
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. Read the rest of this entry »
Tags: code, conversion, convert, lc, lc function, perl, perl code, substitute, substitute group of characters, substitution, translation, translation operator, uppercase to lowercase
Posted in Perl, Programming Languages, Technology | No Comments »
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. Read the rest of this entry »
Tags: 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
Posted in Cisco, Labs, Networking, Protocols, Technology, Troubleshooting | 1 Comment »
December 29th, 2011
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. Read the rest of this entry »
Tags: 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
Posted in Perl, Programming Languages, Technology | No Comments »
