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:
Continued…
Tags: loopback, networking, ospf, routing
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.
Continued…
Tags: containers, linux, lxc, virtualization
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.
Continued…
Tags: bird, cisco, instances, linux, loopback, networking, ospf, routers, routing, vrf
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.
Continued…
Tags: cisco, loopback, networking, ospf, routing, vrf
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.
Continued…
Tags: cisco, iproute2, linux, networking, vrf
By Administrator in All, Linux administration
Every Linux machine that has at least two networking interfaces can be configured to route network packets between these interfaces. Whether or not a Linux box will be capable of routing is determined by the value of the ip_forward kernel parameter. Most modern Linux systems would come with this value set to 0 which means that routing is disabled by default.
In order to enable routing, you can do the following:
Continued…
Tags: forwarding, linux, routing
By Administrator in All, Linux administration, SSH server
Forwarding ports over SSH or the so called SSH tunneling is a very convenient capability of the OpenSSH server. It allows you to establish a secure connection to a service that does not support secure connections provided that you have SSH access to the same machine and tunneling is permitted.
Let’s start with a short and straight-forward description of how SSH tunneling works. Let’s say that you have a remote MySQL server to connect to and it does not support SSL connections. The same server, however, also runs an OpenSSH daemon that you have access to. Using SSH tunneling to connect to the MySQL service securely, pretty much consists of the following:
Continued…
Tags: forwarding, ports, server, ssh, tunneling
By Administrator in All, Linux administration
The command below can be very useful in identifying which folders on your system are containing the largest numbers of files (inodes). It frequently happens that a caching or logging component of a web application goes berserk and starts generating an enormous amount of files in a certain subfolder. Such an event might be trouble if the system imposes inode usage limitations as many web hosting providers do. If we are lucky, the folder would be called “cache” but in the less fortunate cases, the following sequence of commands can come in handy:
Continued…
Tags: files, inodes, linux, unix
By Administrator in All, Linux administration
This article is inspired by a blogpost (http://geekmondo.tumblr.com/) I recently ran into, about the axel program. It made me think that I had always been using the wget command to download files via the HTTP protocol while on the Linux command line and I had never looked for an alternative. Sure, wget is a great, proven, do-it-all tool but is it really the best option for simple HTTP file downloads? I decided to run a very basic test, comparing the download speed of several command line download tools – wget, axel, curl and aria2c.
Continued…
Tags: aria2c, axel, curl, download, linux, wget
By Administrator in All, Apache server, Linux administration, MySQL server
This is just a tiny article that I decided to write because I kept forgetting the single command that quickly creates a functional LAMP (Linux, Apache, MySQL, PHP) server. A system administrator or a web developer might frequently need to set up a basic LAMP environment for experimental purposes.
Continued…
Tags: apache, LAMP, linux, mysql, php, server, ubuntu