CCNA Training Daily Bits - Your Daily Dose of Web and Technology NAT Order of Operation [IP Addressing Services Introduction This document illustrates that the order in which transactions are processed using Network Address Translation (NAT) is based on whether a packet goes from the inside network to the outside network, or from the outside network to the inside network. Prerequisites Requirements Readers of this document should have knowledge of this topic: Network Address Translation (NAT). Components Used This document is not restricted to specific software and hardware versions. Note: The information in this document is based on the Software Version, Cisco IOS® Software Release 12.2(27) Conventions Refer to the Cisco Technical Tips Conventions for more information on document conventions. NAT Overview In this table, when NAT performs the global to local, or local to global, translation is different in each flow. NAT Configuration and Output This example demonstrates how the order of operations can effect NAT. ! The translation table indicates that the intended translation exists. Related Information
Recovery From Corrupt or Missing Software Image on Cisco Catalyst 2900XL and 3500XL Series Switches Introduction This document describes how to recover from a corrupt or missing software image on the Cisco Catalyst 2900XL and 3500XL Series Switches. When this problem exists, the error message error loading flash appears when you boot up after power loss or after an incorrect software upgrade. Note: Trivial File Transfer Protocol (TFTP) may be used to transfer software image files from a PC to your device. Prerequisites Requirements There are no specific requirements for this document. Components Used To create the examples in this document, this equipment is used: Hyperterminal software used in Microsoft Operating Systems. The information presented in this document was created from devices in a specific lab environment. Conventions For more information on document conventions, refer to the Cisco Technical Tips Conventions. Problem If you receive the error loading flash message, this indicates that there is a problem loading the current image in Flash. Unplug the power cable. Solution
Using Linux iptables or ipchains to set up an internet gateway / firewall / routerfor home or office. Note: References to ipfwadm and ipchains refer to older deprecated software. Note: Red Hat 7.1-9.0 and the default Linux 2.4 kernel may use ipchains or iptables but not both. Iptables is the preferred firewall as it supports "state" and can recognize if a network connection has already been "ESTABLISHED" or if the connection is related to the previous connection (required for ftp which makes multiple connections on different ports). Ipchains can not. Ipchain rules take precedence over iptables rules. Red Hat 7.1 will not support ipchains unless that option is configured (during install or later). GUI configuration: iptables: The GUI configuration tool /usr/bin/redhat-config-securitylevel can be used to choose a preconfigured firewall (High, Medium or no firewall) or it can be used to manually configure rules based on the network services your server will offer. The default Red Hat 7.1+ Linux 2.4 kernel is compiled to support both iptables and ipchains. iptables: ipchains:
OpenDNS From DD-WRT Wiki OpenDNS is a free DNS (Domain Name Server) service which makes internet browsing safer and allegedly faster. By simply using their DNS servers instead of your ISP's you are automatically protected from their list of Phishing websites. However, in order to restrict a variety of adult website content you will need to create a free account with them, register your IP address and select the categories you want restricted (i.e. sexuality, nude, pornography, lingerie, grotesque, etc...). Since most of us have DHCP assigned WAN IP addresses that change periodically we need to instruct our router to tell OpenDNS what our new IP address is when it changes. [edit] Basic Setup In order to configure dd-wrt with OpenDNS you need to specify the OpenDNS DNS servers in the control panel. Option 1 - Configure DHCP with OpenDNS DNS server If you want the DNS servers to be queried in the order they're listed rather than randomly: Option 2 - Configure DNSMasq for OpenDNS DNS forwarding Or
Web interface for OpenWrt and more - X-Wrt.org 10 quick tips to make Linux networking easier | 10 Things | TechRepublic.com Linux makes networking simple and secure -- if you know a few tricks. Jack Wallen shares some pointers to help admins knock out various Linux networking tasks with a minimum of effort. Linux makes networking simple and secure -- if you know a few tricks. Jack Wallen shares some pointers to help admins knock out various Linux networking tasks with a minimum of effort. Networking is a must-have on all levels of computing. Be it home or corporate, networking is the one aspect of computing that is, without a shadow of a doubt, a deal breaker. Note: This information is also available as a PDF download. #1: Make use of your /etc/hosts file The hosts file is used for static host names and offers a quick way to create networking shortcuts. For example, if I use one machine for a backup location at IP address 192.168.1.101, I could enter: 192.168.1.101 backups Now if I have to connect to that machine, say with secure shell, I can just type ssh -v -l username backups to make the connection. DEVICE=eth0
How to Build a Simple Wireless Authenticated Gateway (SWAG) Using OpenBSD :: Hack In The Box :: Keeping Knowledge Free By: Rosli Sukri Now, without spending a lot of money you to can build an authenticated gateway solution to verify your WIFI users. First and foremost you need to get your hands on the coolest free BSD system for firewalls and security devices. In this example I will be using OpenBSD3.6 stock standard as a build and a base system (but I guess you could use FreeBSD5.3 – me thinks the newer FreeBSD are getting a bit bloated but the background fscking, fscking rocks dude!) Once you have installed your neighborhood OS in your server (go ahead and install all the packages from the OpenBSD installation CD, heck I have 40G worth of SATA drive on my brand spanking new Dell 1U server so I don't really care) you only need to change a couple of files within your /etc directory before you can start rocking. The Setup By the way my rig is a Dell 1U server with 4 NIC cards and a lot of RAM. The ultimate goal is to have 2 internal network segments and 1 uplink to the Internet. /etc/rc.conf.local 1.) 2.)