Thursday, October 27, 2005

TCP/IP Subnetting Example


1) What Sub-net Mask Should I use ?

How many subnets are required ? = 27

Convert this number to low order Binary = 00011011

How many bits used to represent number ? = 5

Convert number of bits used to high order binary and convert to decimal = 248

2) How many subnets do I actually get using this mask ?

128 64 32 16 8 4 2 1

1 1 1 1 1 0 0 0
How Many bits were used for the subnet mask = 5
25 - 2 = no of subnets = 30

3) What are my subnet IDs

128 64 32 16 8 4 2 1

1 1 1 1 1 0 0 0 = 8

Starting at this number jump in increments of the same value (eg 8,16,24,32 etc..)
Until 1 below the subnet mask value ( i.e upto 240) There should be as many Ids as your calculated subnets figure.

4) How many HOSTS do I get per Subnet?

How many bits are remaining for Host ID? = 3 from third octet and 8 from fourth octet ie = 11 bits

11111111 11111111 11111000 00000000
255 255 248 0

2 11 -2 no of hosts per subnet = 2,046

5) What other HOSTS are on my Subnet ?
What value did you increment by {see 2) } = 8s
Which range does the subnet portion of your IP address fit into ?
Are the other hosts in the same range as you ?

If your IP address is with a subnet mask of you fit in the range
Between ->

Are these hosts in the same range as you = yes = no = no = yes

Thursday, October 20, 2005

Tech Links

Intro to Tcp/IP

Ireland ISP Point of Presence

Irish Free Dial-Up ISP Settings - Software
Eircom Net FreeAccess number - 1892 150 150Username - eircomnetPassword - eircomnetPrimary DNS - DNS - mail server (POP) - mail2.eircom.netOutgoing mail server (SMTP) - mail2.eircom.netnntp (news) server - news1.eircom.netwebspace ftp server - homepage.eircom.netftp server port number - 21default web folder - public_htmldefault web page - index.htm

IOLFreeAccess Number - 1890 924 042

Username - free
Password - freePrimary
DNS - DNS - mail server (POP) - pop.iolfree.ieOutgoing mail server (SMTP) - mail.iolfree.ieProxy - proxy.iolfree.iePort - 8080OceanfreeAccess Number - 1890923204Username - OceanfreePassword - OceanfreePrimary DNS - DNS - mail server (POP) - mail.oceanfree.netOutgoing mail server (SMTP) - smtp.oceanfree.netMore settings can be found at FreeDialupIsps on IIU Wiki

Wednesday, October 19, 2005

Exchange Service Pack 2 lands

Finally, Exchange SP2 for Exchange 2003 is available for download here

David Houston who manages the SBS Ireland Users group site was the first person to let me know.

So what! I here you say, well firstly it gives us the ability to increase the information store from 16GB to 75 Gb in size which has to be welcome as I am sure a lot of us and our customers are coming close to the 16GB limit.

The update also includes support for SenderID
which could potentially give us a decent tool to limit if not prevent someone spoofing a mail from our/your smtp domain.

Hands up how many of us are getting automated emails from Anti Virus software stating that a mail which we never sent contained a virus.

Good deed for today, please convince all those sys admins you know to turn off the email response that most AV products send to the sender of an infected mail because let's be honest in most cases the email address is spoofed.

The best post I have seen which both details the installation and the benefits of Exchange's new Service Pack has to be Vlad's on his blog.

who I had the pleasure to meet in SMB Nation in September but unfortunately I didn't get a chance to talk to properly, great article Vlad.

Regards Mark

Tuesday, October 18, 2005

APC Java issue causes Services to Hang

Thanks to Rob for this one.

Believe it or not the APC software usually version 6.x of Powerchute which a lot of IT shops run which provides the monitoring function for the UPS can cause a Windows Server to be become extremely unstable.

Basically the problem stems from an issue with the Sun java runtime which causes an event ID 7022 Service unresponsive.

Basically if you have a Windows 2000 / 2003 server that is extremely unresponsive before you suspect DNS / Active Directory or any other core service just check if are running a version of Powerchute prior to Version 7 and this just might be your issue.

As I was browsing for something else I came across Mark Wilson's great blog and a very detailed posting on how he resolved the issue

Regards Mark