Posts Tagged ‘ipconfig’

Fix temporary DNS problems on Windows – ipconfig /flushdns

Monday, March 17th, 2014

fix temporary dns issues ipconfig /fush
My internet connection is coming router over a strange Belarusian ADSL modem "Промсвязь". This device serves as ADSL modem and a Wireless Router.
promsviaz_belarusian_adsl_and_wifi_modem

Periodically I'm experiencing issues with DNS, where there is internet but DNS resolving stops woring even though in ipconfig /all I can see DNS settings are proper:

C:\Users\hipo> ipconfig /all

...
Wireless LAN adapter Wireless Network Connection:

   Connection-specific DNS Suffix  . :
   Description . . . . . . . . . . . : Intel(R) Centrino(R) Ultimate-N 6300 AGN
   Physical Address. . . . . . . . . : 3C-A9-F4-4C-E7-98
   DHCP Enabled. . . . . . . . . . . : Yes
   Autoconfiguration Enabled . . . . : Yes
   Link-local IPv6 Address . . . . . : fe80::5d2f:97b8:9e1a:2b13%63(Preferred)
   IPv4 Address. . . . . . . . . . . : 192.168.100.2(Preferred)
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Lease Obtained. . . . . . . . . . : March 17, 2014 16:57:40 PM
   Lease Expires . . . . . . . . . . : March 18, 2014 16:57:40 PM
   Default Gateway . . . . . . . . . : 192.168.100.1
   DHCP Server . . . . . . . . . . . : 192.168.100.1
   DHCPv6 IAID . . . . . . . . . . . : 1094494708
   DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-19-CB-1A-5D-A4-5D-36-5A-EB-84

   DNS Servers . . . . . . . . . . . : 8.8.8.8
                                       192.168.100.1
                                       8.8.4.4

   NetBIOS over Tcpip. . . . . . . . : Enabled

 

The fix to situation is to Restart Promsvijazy and restart my Notebook. As this fix takes a lot of time I found another "work around". Make Windows Flush its DNS servers (forget old DNS servers and re-assign them again)

C:\Users\hipo> ipconfig /flushdns

Windows IP Configuration Successfully flushed the DNS Resolver Cache.


 

Other useful commands to make connection re-initiate completely are:

ipconfig /renew

Renews all Adapter settings (Lan, Wiki, PPP etc.) – re-assign IPs / re-initiate connections and

ipconfig /release

Releases any established connection

How to renew IP address, Add Routing and flush DNS cache on Windows XP / Vista / 7

Friday, November 25th, 2011

There are two handy Windows commands which can be used to renew IP address or flush prior cached DNS records which often create problems with resolving hosts.

1. To renew the IP address (fetch address from DHCP server)C:> ipconfig /release
C:> ipconfig /renew

In above cmd ipconfig /release will de-assign the IP address configured on all Windows LAN and Wireless interfaces, whether ipconfig /renew will send request for IP address to the DNS server.

To unassign and assign again IP address from DHCP server only for a particular LAN or WLAN card:

C:> ipconfig /release LAN
C:> ipconfig /renew LAN
C:> ipconfig /release WLAN
C:> ipconfig /renew WLAN

2. Adding specific routing to Windows

Windows has a Route command similar by syntax to Linux’s route command.
To add routing via a specific predefined IP addresses on Windows the commands should be something like:

C:> Route add 192.168.40.0 mask 255.255.255.0 192.168.41.253
C:> Route add 0.0.0.0 mask 0.0.0.0 192.168.41.254
The first command adds IP 192.168.40.0 in the network of 255 hosts to be routed via 192.168.41.253
The second one adds 192.168.41.254 as a default gateway for all outbound traffic from the Windows host.
To make permanent routing -p switch is used.
3. To clear Windows DNS cache (flush DNS cached records) C:> ipconfig /flushdns
This will clear all IP records corresponding to hostnames previously cached on the Windows host. Using ipconfig /flushdns is especially handy when IP address for a specific DNS host is changed. Flushing the Windows DNS cache can save us a lot of waiting before the domain example.com starts resolving to the new IP address let’s say 1.2.3.4 instead of the old one 2.2.2.2