IPv4 CIDR Chart

VLSM/CIDR Reference Table (IPv4 Subnetting Chart)
Class Prefix  Subnet Mask  Subnets  Hosts / Usable IPs  Bits used
C  /31  255.255.255.254  128  2 (ppp only)  7 / 1
 /30  255.255.255.252  64  4 (2)  6 / 2
 /29  255.255.255.248  32  8 (6)  5 / 3
 /28  255.255.255.240  16  16 (14)  4 / 4
 /27  255.255.255.224  8  32 (30)  3 / 5
 /26  255.255.255.192  4  64 (62)  2 / 6
 /25  255.255.255.128  2  128 (126)  1 / 7
 /24  255.255.255.0  0  256 (254)  0 / 8
B  /23  255.255.254.0  128  512 (510)  7 / 9
 /22  255.255.252.0  64  1024 (1022)  6 / 10
 /21  255.255.248.0  32  2048 (2046)  5 / 11
 /20  255.255.240.0  16  4096 (4094)  4 / 12
 /19  255.255.224.0  8  8292 (8290)  3 / 13
 /18  255.255.192.0  4  16384 (16382)  2 / 14
 /17  255.255.128.0  2  32768 (32766)  1 / 15
 /16  255.255.0.0  0  65536 (65534)  0 / 16
A  /15  255.254.0.0  128  131072 (- 2)  7 / 17
 /14  255.252.0.0  64  262144 (- 2)  6 / 18
 /13  255.248.0.0  32  524288 (- 2)  5 / 19
 /12  255.240.0.0  16  1048576 (- 2)  4 / 20
 /11  255.224.0.0  8  2097152 (- 2)  3 / 21
 /10  255.192.0.0  4  4194304 (- 2)  2 / 22
 /9  255.128.0.0  2  8388608 (- 2)  1 / 23
 /8  255.0.0.0  0  16777216 (- 2)  0 / 24
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Adding RedHat DVD as Repository

When we try out a new linux OS its always a pain to download and install all the software and  add packages we needs on that. Its even worse if you don?t have an unlimited connection. But actually most of the software we need is already there in the CD/DVD in which the operating system comes with. So how do we install from the DVD then rather than from the internet?
For this you need to add the DVD as a repository so that rpm client picks up the rpm from the DVD and wont go to internet for it.
The Procedure and Files to be modified is a bit different for each OS so i will cover Red Hat Linux in this post.
In RHEL the repo list is maintained in the folder /etc/yum.repos.d/ . So lets create a new file in this directory , say lets call it rhel-cd.repo.
The Contents of this file should be as follows:

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Putty Auto Login Via Command Line

So lets say you want to open a new PuTTY session to a certain IP Address and have it automatically enter your username for you.

C:\putty.exe username@192.168.0.1

Now lets do the same thing but with a password too.

C:\putty.exe username@192.168.0.1 -pw password

The two above are fine if you don’t need to use any of the provided settings you get from within PuTTY (e.g. Tunnels, Proxy’s, Color Schemes etc) but if you’re like me and you need to use Tunnels to tunnel into a server using a number of ports then the simplest way to do is this to create a new PuTTY session and then use the following parameters.

C:\putty.exe -load “Session Name” -l username -pw password
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Exchange 2003 to 2010 mail flow issue

Durring the exchange 2010 install the routing group connector didn’t get created so we need to run the following command in the exchange management shell to create the routing group connector:

New-RoutingGroupConnector -Name "2010-2003" -SourceTransportServers "Ex2010Hub1.contoso.com" -TargetTransportServers "Ex2003BH1.contoso.com" -Cost 10 -Bidirectional $true -PublicFolderReferralsEnabled $true

You also want to make sure that your smtp virtual server on exchange 2003 and exchange 2010 is configured to work on port 25 or you will still have mail flow issues.

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