Subneting?

cisco training · 11-30-2010, 05:01 AM

I have been studying for the CCNA exam. Right now I"m studying
subnetting so I thought I might investigate the network where I work.

This is what I found.

10.31.1.125 with a subnet mask of 255.255.255.0

Other computers have IP addresses like 10.31.1.211 with a subnet mask
of 255.255.0.0

According to what I have learned 10.31.1.125 is not a valid host
address for a subnet mask of 255.255.255.0
Am I reading the book wrong? I can ping 10.31.1.211 from 10.31.1.125.
There is no router between them. HOw is this working..? Is windows
ignoring the third octet of the subnet mask for 10.31.1.125?

tr7man · 11-28-2011, 10:15 PM

Examine these networks:

IP Address-----Subnet Mask------Subnet---------IP Range
10.31.1.125----255.255.255.0----10.31.1.0/24----10.31.1.1 - 10.31.1.254
10.31.1.211----255.255.0.0------10.31.0.0/16----10.31.0.1 -10.31.255.254

Did both of these pc's have DHCP assigned IP addresses or were they manually assigned a static IP address and subnet mask? It's possible someone mistakenly entered the incorrect subnet mask on one of these pc's with a manually assigned static IP address.

Both of these IP addresses fit into the IP Ranges specified by both subnet masks.

11-30-2010, 05:01 AM	#1 (permalink)
cisco training Banned Join Date: Jun 2010 Posts: 3	Subneting? I have been studying for the CCNA exam. Right now I"m studying subnetting so I thought I might investigate the network where I work. This is what I found. 10.31.1.125 with a subnet mask of 255.255.255.0 Other computers have IP addresses like 10.31.1.211 with a subnet mask of 255.255.0.0 According to what I have learned 10.31.1.125 is not a valid host address for a subnet mask of 255.255.255.0 Am I reading the book wrong? I can ping 10.31.1.211 from 10.31.1.125. There is no router between them. HOw is this working..? Is windows ignoring the third octet of the subnet mask for 10.31.1.125?

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11-28-2011, 10:15 PM	#2 (permalink)
tr7man Junior Member Join Date: Nov 2011 Posts: 1	Examine these networks: IP Address-----Subnet Mask------Subnet---------IP Range 10.31.1.125----255.255.255.0----10.31.1.0/24----10.31.1.1 - 10.31.1.254 10.31.1.211----255.255.0.0------10.31.0.0/16----10.31.0.1 -10.31.255.254 Did both of these pc's have DHCP assigned IP addresses or were they manually assigned a static IP address and subnet mask? It's possible someone mistakenly entered the incorrect subnet mask on one of these pc's with a manually assigned static IP address. Both of these IP addresses fit into the IP Ranges specified by both subnet masks.