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Showing posts from January, 2014

Cisco Router a DHCP Server

Here is the procedure how to run your Cisco Router as DHCP server. A small topology how to configure DHCP server in Cisco Router. Now use the following command to configure the Router running as DHCP server. Then verify from the PC connected to that interface. You can copy following command  and paste into your Router ******output omitted ******** ! ! ! ! ip dhcp excluded-address ! ip dhcp pool test  network  default-router  dns-server ! ! ! ! ! ! ! ! ! ! ! ! ! interface FastEthernet0/0  ip address

550 Access denied Invalid HELO name

On your outlook express while sending the emails and you get following error. Cannot send the message. Verify the e-mail address in your account properties. The server responded: 550 Access denied - Invalid HELO name (See RFC2821 Follow below procedure to solved the issue.  1. Click Tools>Account 2. Select"View or change existing e-mail accounts" and click next 3. Select desire email account and click change 4. Click on "More Settings" at bottom of the page 5. Select on "Outgoing server" tab 6. Check "My outgoing server (SMTP) requires Authentication" 7. Select "use same settings as my incoming email server" 8. Click "Ok" 9. Press Next and Finished 

Linux Tools to see What Process consume Bandwidth

I have to day to day network troubleshoot and I need such a tool which shows what program consume the network bandwidth. So the Nethogs tool is small net top tool which fit exactly under my requirements. Here is the process to install and use of the tool. The tool monitors traffic going to and from a machine, by per process basis. jpudasaini@jpudasaini:~$ sudo apt-get install nethogs   *****Output******* [sudo] password for jpudasaini: Reading package lists... Done Building dependency tree       Reading state information... Done The following packages were automatically installed and are no longer required:   kde-l10n-engb linux-image-generic Use 'apt-get autoremove' to remove them. The following NEW packages will be installed:   nethogs 0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded. Need to get 28.3 kB of archives. After this operation, 105 kB of additional disk space will be used. Get:1 saucy/universe

Open DNS Recursive Resolver Attack

Dear blog reader, few days back I have face a huge DNS Amplification/Reflection attack from Mikrotik (MT) router. The Attack has been organized from different source to different destination.  This attack also has been seen in different vendor router like d-link di-1705b, Buffalo,AirLive, Cisco(Cisco Systems, Inc. Firmware: 4608) The Attack is possible because of MT router apply following tcp and udp packet filter destination port 53.  IP>firewall>filter rules chain=input action=drop protocol=udp in-interface=ether1-WAN dst-port=53 chain=input action=drop protocol=tcp in-interface=ether1-WAN dst-port=53 Same rule can be maintain for other router to block and disable resolver. Please Note: in-interface should be your WAN port. How to check your IP is used as open resolver Linux command #dig -t A @ Note: Replace with your IP address