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  • How to fix Exchange & Outlook connection issues over IPSec VPN

    Recently we had this problem with this problem with an Exchange 2003 server in the HQ and Outlook Clients in a particular branch office. The Branch office connects into the HQ through a site to site IPSec VPN using Juniper Netscreen SSG20 firewalls on either end of tunnels.

    The Problem
    The Outlook clients would connect OK but suddenly loose connection to the Exchange server and never connect back. The Outlook Client status will say "Disconnected". The client PCs will however be able to ping the server and network connections look OK. This happened in random times and sometimes when sending large emails.

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  • How to enable Path MTU Discovery in Juniper Netscreen Firewalls (ScreenOS)

    If you have site to site IPSec VPNs configured between two network with your Juniper Netscreen or SSG firewalls and clients from one network access servers or services from the other network then it is advisable to enable Path MTU Discovery support on the Juniper firewalls.

    Juniper Netscreen or SSG firewalls running Screen OS by default disable the Path MTU Discovery support. This means, when an IP Packet with DF bit set ("1") in the ip Header and its size after IPSec Encapsulation is more the MTU of the Juniper VPN Firewall arrives at the VPN Firewall, the firewall will ignore the "DF" bit and simply fragments the packets and forwards it to the appropriate tunnel interface. This can cause serious problems with some applications. A classic example is the Microsoft Applications that rely on NetBIOS over TCP/IP which wouldn't prefer the packets being fragmented (and hence DF set).

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  • Dr.TCP – Fine Tune TCP/IP Parameters including MTU in Windows

    Dr.TCP is a simple but powerful utility that can let you fine tune the TCP/IP parameters for your Network Interface Card (NIC). It works on Windows XP, 2003,2000.

    Dr.TCP takes the hassle out of editing the Windows Registry and modifying keys to fine tune the TCP/IP Parameters at

    [HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\<AdapterID>] 

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  • Yersinia – Free Network Testing tool for CDP,STP,VTP,DHCP,DTP,ISL,802.1Q,802.1X

    Yersinia is a free Network Penetration testing tool used to test and analyse some of the most commonly used protocols on your network. Penetration testing tools of this kind will provide deep insight on network security issues. Yersinia is a UNIX based tool that works on Linux, Solaris 8, FreeBSD.

    NOTE: The tool is described as a tool to perform network tests and exercise responsible actions when performing tests which includes obtaining the permission from responsible authorities. DO NOT USE THIS TOOL FOR ANY UNAUTHROSIED HACKING PURPOSES

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  • mturoute – Free utility to find the MTU Value to a host or IP Address

    One of the most important thing that is ignored most of the time while troubleshooting a network problem to a host or a network is checking the MTU related issue. This makes more sense in situations like troubleshooting VPN related issues.

    MTUROUTE is a small but smart utility that uses ICMP pings of various sizes in order to determine the MTU values (Maximum Transmission Unit) on the path between itself and the target system. MTUROUTE can operate in normal mode where it sends multiple ICMP packets to each hop on the path to identify the smallest MTU between the host and hop or in a Traceroute mode where it will attempt to determine the lowest MTU between the local host and each hop in the communication.

    It is important to note that care has to be taken as it generates muti fold ICMP traffic as it tries to determine the MTU Values.

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  • File Shredder – Free Opensource tool to Secure File Destruction

    Secure destruction of data like personal details, banking information, confidential company information or critical customer data when they are no longer required is very important to information security for the simple reason that they can always be recovered in many ways from the hard disk. This is even more important when you sell or throw away your old PCs. Simply deleting the files from the PC doesn't really remove the files for good. They can always be recovered. FileShredder just protects you from that. File Shredder is an opensource free file secure destruction software for permanent removal of critical confidential files from the hard disk. With File Shredder you can remove files from your hard drive without fear they could be recovered. File Shredder has been developed as fast, safe and reliable tool to shred company files.

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  • How to add Static routes and Default routes in Cisco IOS

    Static routes allow administrators to configure routes for specific hosts or networks manually as against learning dynamically using routing protocols like RIP, EIGRP and OSPF. Static routes basically tells the Cisco IOS of which next hop router or the exit interface on the local router that the traffic for a particular host or network needs to be passed to.

    To add a Static Route in cisco ios based switches and routers the following is the command syntax. This command is run from the global configuration mode.

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