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By Administrator in All, Linux administration

When it comes to redirecting TCP traffic, rinetd is a pretty old-school, frequently overlooked, simple and very efficient way to go. rinetd is an application layer port forwarder which, unfortunately, only supports the TCP protocol and not UDP. It is somehow similar to the once popular super-server daemons such as inetd, xinetd and rlinetd but it is simpler and best suited for redirecting TCP connections.

The settings of the rinetd daemon are by default stored in the /etc/rinetd.conf file and they follow a pretty intuitive syntax:

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By Administrator in All, Routing protocols

The purpose of stub areas in an OSPF network is to reduce the amount of routing information that routers within a single area have to manage. Essentially, this is achieved by the ABR of a stub area filtering all external advertisements and replacing them with a default route. In most cases, this could considerably affect the size of the routing table that must be maintained internally.

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By Administrator in All, Routing protocols

The OSPF and IS-IS routing protocols share a number of common features as both are link-state routing protocols based on the Dijkstra SPF (Shortest Path First) algorithm. Both protocols prevent routing loops, converge quickly, support a two-level hierarchy and variable length subnet masking.

Despite their many similarities, the two routing protocols do have several differences some of which are considered to be benefits of IS-IS over OSPF:

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By Administrator in All, Linux administration, SSH server

The sshfs tool is a file system client application based on the SSH communication protocol. It could be of great help when you want to mount a remote file system locally and work with the remote files as if they were on your own machine. Most Linux distributions would provide a pre-compiled package for the sshfs client so you should be able to quickly install it on your PC using apt-get, yum, etc.

Using sshfs is actually quite simple. All you need to make sure is that you have SSH connectivity to the remote host and that the SSH server has the SFTP Subsystem enabled.

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By Administrator in All, Linux administration

When working on the command line in Linux or Unix, it could be very useful to be able to search for files that have been last modified on a specific date.

Strangely enough, the almighty find command does not offer a single option that would allow you to find all files modified on let’s say May 31, 2011. Of course, you could use the -mtime option but it would require you to calculate the exact number of days that have passed since the target date, which is not always a straight-forward task.

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By Administrator in All, Cisco, Routing protocols

We are publishing this short post as we noticed a number of visitors to our website who have landed here via related search queries.

So, the main advantages of using a loopback interface on a Cisco router with OSPF enabled are:

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By Administrator in All, Linux administration

On my laptop, I have a VMWare virtual machine for testing. It is an Ubuntu Linux distribution with 20 GB of disk size and 512 MB of memory. Recently, I needed more Linux machines for simulating multi-router network environments. Because installing VMWare virtual machines is too much for the purpose, I decided to try the container-based virtualization supported by the Linux kernel – LXC. Below are the summary steps to add two new virtual machines on my ubuntu host with two network interfaces each.

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By Administrator in All, Linux administration, Routing protocols

This article illustrates how a scenario, similar to the one from our previous post Simulating VRF with OSPF instances on Cisco, could be implemented using Linux-based routers.

Scenario details and network topology

There are two companies A and B with offices in different towns. The offices are connected to the same service provider (SP). The goal is to establish layer 3 connectivity between each company’s offices in different towns, while maintaining separation of routing information and data traffic among different customers. A standard layer 3 VPN task, however, we try to accomplish it using neither MPLS nor VRF.

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By Administrator in All, Cisco, Routing protocols

Layer 3 separation with OSPF instances – conceptual overview

The main idea is that each provider router will be aware of all customer routes while each customer router will only learn routes relevant to their network. Separate OSPF instances are running for each customer, and are enabled on provider facing interface. One OSPF instance number 1 collects routes from all customers through redistribution. We will call it the super instance. Then, the routes are spread throughout the OSPF domain. The super instance is enabled only on provider-to provider links.

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By Administrator in All, Linux administration, Routing protocols

VRF Lite Introduction

The idea behind VRF is to separate IP networks in different groups. There are other ways to achieve layer 3 separation such as access lists, route filtering and NAT. VRF uses separate routing tables to divide network layer information. Packets are classified based on the interface they are received on. A single interface can be associated with a single VRF instance. VRF is very popular with MPLS and layer 3 VPNs offered by Service Providers. VRF Lite is the VRF implementation without MPLS.

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