Showing posts with the label networking


GNS3 Version 2 Released!
For the uninitiated, GNS3 is an OpenSource, cross-platform network virtualization software, that’s “used by hundreds of thousands of network engineers worldwide to emulate, configure, test and troubleshoot virtual and real networks. GNS3 allows you to run a small topology consisting of only a few devices on your laptop, to those that have many devices hosted on multiple servers or even hosted in the cloud.“
Ever since the crowd-funding campaign a couple of years ago, the project has benefited from a surge in development, culminating in the latest release announced today. By the way, there’s a GNS3 Academy now, bringing a more democratized approach to training through the use of OpenSource software and affordable prices.  Hopefully, this will do for Networking courses and labs what Udemy, edX, and others have done for other technology-related fields.  Unfortunately, the proprietary hardware and software of industry giants like Cisco or VMWare will continue to be ba…

RHEL7 Fedora as Network Router and Gateway

Hardware Requirements:2 Ethernet Network Cards: 1 for WAN; 1 for LANOptional Wireless Router for wifi
Software Requirements:NIC Configuration Filessysctl Kernel ParametersFirewall Configurationdhcpd Server For the sake of clarity the two network cards will be called ifcfg-wan (WAN) and ifcfg-lan (LAN); make the necessary changes for your environment accordingly, e.g. eth0, ens1, enp0s77, etc., as I will not outline how to make naming changes for hardware devices.  The configuration files for the relevant network adapters/cards are located in /etc/sysconfig/network-scripts/ifcfg-wan and /etc/sysconfig/network-scripts/ifcfg-lan files.

First, make sure all the interfaces are "down" and the ethernet cables are unplugged from both adapters.  Assuming you're not using NetworkManager this can be accomplished on the commandline with "ifdown wan" and/or "ifdown lan".

Next, check the system's network activity for open ports and close them all for now:

# netst…

Troubleshoot USB-Printer Connected to Router

I had complained about a flood of error messages being continuously printed out every time a print job was sent to the USB-printer attached to my Asus AC56U router with merlin-378.55_beta1. Yesterday, after I had reverted to the official asuswrt firmware to troubleshoot the printer-sharing feature, I used nmap on my laptop to see the open common ports on the clients on my network:

Code: # nmap -T4 -F The router displayed two ports related to the printer service:

Code: Host is up (0.0065s latency). Not shown: 94 closed ports PORT STATE SERVICE 53/tcp open domain 80/tcp open http 139/tcp open netbios-ssn 445/tcp open microsoft-ds 515/tcp open printer 9100/tcp open jetdirect Anyway, long story short, I had been using the socket:// path to the printer; changing the configuration on my laptop (CUPS-server) to point to lpd:// finally resulted in SUCCESS!

Virtual Interfaces and VLANs in Fedora20

Setting up VLAN interfaces in Fedora20 VLAN is an acronym for Virtual Local Area Network. Several VLANs can co-exist on a single physical switch, which are configured via Linux software and not through hardware interface (you still need to configure actual hardware switch too).

Hardware Device Requirements
• To be able to use VLANs you will need a switch that support the IEEE 802.1q standard on an Ethernet network.
• You will also need a NIC (Network Interface Card) that works with Linux and support 802.1q standard. Setting Up 802.1q VLAN Tagging This is based on Fedora documentation, specifically F17-System Administrators Guide .
• First, ensure that the 8021q kernel module is loaded with the following command:
# lsmod | grep 8021q# modprobe 8021q is the command to load it if no output results from the grep command above.
• Configure the physical interf…

localtimeUpon a successful login into the VM system, changing the Timezone to which the system’s time is configured can be accomplished by changing the /etc/localtimelink. NOTE
Since the implementation of systemd in RHEL7, changing the system’s default
timezone manually is not persistent; as the /etc/localtime link gets recreated
by systemd after a reboot, the user must use timedatectl to make the desired
change persistentTo change the default timezone to the timezone of Chicago, for example, execute the following as the root user:# cd /etc/ # ls -alh localtime /etc/localtime -> ../usr/share/zoneinfo/America/NewYork # unlink /etc/localtime # ln -s /usr/share/zoneinfo/America/Chicago /etc/localtime /etc/localtime -> ../usr/share/zoneinfo/America/Chicago In the above example, we have changed the timezone from the previous value, pointing to the timezone to which “NewYork” belongs, to the timezone of Chicago.The systemd Method for Changing the Default TimezoneSynops…

Configure rsyslog Server on Fedora

It can be very beneficial for system administrators and network administrators, especially, to log system messages from other machines on the network to a centralized hub. Fedora 20 uses rsyslog as the default syslogd service; this allows administrators to configure remote logging. I'll be detailing the necessary configuration steps of rsyslog in Fedora 20 to allow logging messages from a DD-WRT router. This will entail Edit /etc/rsyslog.confSet up firewall rule to allow incoming connection to serverConfigure DD-WRT router to send syslogd messages to our server
rsyslog server Our server will be the Fedora 20 machine. There are two configuration files in the /etc/ directory that are of interest to us: /etc/rsyslog.conf /etc/sysconfig/rsyslog However, the latter file is not useful anymore as it states: # Options for rsyslogd # Syslogd options are deprecated since rsyslog v3. # If you want to use them, switch to compatibility mode 2 by "-c 2" # See rsyslogd(8) for mor…

Troubleshoot JavaScript Functionality--Firefox Browser and DD-WRT Network Router

HTML5 is here! On October 28th, 2014 the HTML Working Grouppublished HTML5 as W3C Recommendation. This specification defines the fifth major revision of the Hypertext Markup Language (HTML), the format used to build Web pages and applications, and the cornerstone of the Open Web Platform.

When the talk of HTML5 comes up generally it's understood that, for the most part, CSS3 and JavaScript are an intricate part of the "whole". Extended features such as responsive design among other things are nothing without all three languages. JavaScript in particular uproots the "operating system" and unshackles users from the confinement of locally-run software with seemingly boundless potential.

Well, if that wasn't a loaded statement then you still have faith that I know what I'm talking about. Regardless, this post is mainly meant to help troubleshoot the possible causes of a half-assed web-experience followed by constant, nagging banners suggesting that you…

wpa_supplicant and wifi in RHEL 7

If you have a desktop environment set up in Red Hat Enterprise Linux 7, chances are that you might have GNOME installed as it is the "default".  NetworkManager is pulled in as a dependency package of GNOME and it's integrated into gnome-shell in the top panel as a widget.  While NetworkManager is a great tool as it consolidates many different networking tools and facilitates the network configuration for many different use-cases, there might be instances where its broad reach becomes an obstacle rather than a benefit to system administrators.  One such instance is when dealing with network bridging.

Recently I was trying to set up a network bridge on my laptop, as it's equipped with a wifi adapter and an ethernet adapter, in order to dedicate the ethernet interface to a virtual machine in Red Hat 7--or at least to "share" it.  Bridged networking (also known as physical device sharing) is used to dedicate a physical device to a virtual machine. 
So, since w…

fail2ban configuration in Fedora/RHEL

The configuration files in Fedora20 for fail2ban are located in the /etc directory under /etc/fail2ban/
with further sub-directories for actions, filters and jails.drwxr-xr-x.2 root 4.0K May 162014 action.d drwxr-xr-x.2 root 4.0K Mar 192014 fail2ban.d drwxr-xr-x.2 root 4.0K May 162014 filter.d drwxr-xr-x.2 root 4.0K Mar 192014 jail.d -rw-r--r--.1 root 2.1K Mar 142014 fail2ban.conf -rw-r--r--.1 root 33 Dec 1000:16 fail2ban.local-rw-r--r--.1 root 14K Dec 1001:06 jail.conf -rw-r--r--.1 root 16K Dec 1000:54 jail.conf.rpmnew -rw-r--r--.1 root 805 Dec 1007:48 jail.local-rw-r--r--.1 root 1.5K Mar 142014 paths-common.conf -rw-r--r--.1 root 606 Mar 142014 paths-debian.conf -rw-r--r--.1 root 649 Mar 142014 paths-fedora.conf -rw-r--r--.1 root 1.2K Mar 142014 paths-freebsd.conf -rw-r--r--.1 root 290 Mar 142014 paths-osx.confNOTE: In order to preserve your edits and customizations you should create separate *.local files, as the normal *.conf files (may) get overwritten during an upgrade.…