IP Subnet Mask

It seems that something other than me periodically sets subnet mask on
my Win'98SE computer to "255.0.0.0". IPConfig /release_all and IPConfg
/renew_all correctly resets it to "255.255.255.0".

My Linksys router shows internal mask "255.255.255.0". I have DHCP on.

I checked TCP/IP properties and I have get IP automatically checked.

Any ideas where the "bad" mask could be coming from?

TIA, Eugene

"Eugene F." wrote in message
oups.com...
It seems that something other than me periodically sets subnet mask on
my Win'98SE computer to "255.0.0.0". IPConfig /release_all and IPConfg
/renew_all correctly resets it to "255.255.255.0".

My Linksys router shows internal mask "255.255.255.0". I have DHCP on.

I checked TCP/IP properties and I have get IP automatically checked.

Any ideas where the "bad" mask could be coming from?

TIA, Eugene

Default subnet masks are based on the IP address classes.

Hugh,

Thank you very much for the reply.

Default subnet masks are based on the IP address classes.

What does it mean exactly? Sorry, but networking is not my cup of tea.

"Eugene F." wrote in message
ups.com...
Hugh,

Thank you very much for the reply.

Default subnet masks are based on the IP address classes.

What does it mean exactly? Sorry, but networking is not my cup of tea.

It means that the network IP address range that you are using
is categorized as class A, ergo, the default subnet mask
used on a reset will be the class A default, 255.0.0.0

"Eugene F." wrote in message
ups.com...
Hugh,

Thank you very much for the reply.

Default subnet masks are based on the IP address classes.

What does it mean exactly? Sorry, but networking is not my cup of tea.


this might explain it for you

An IP address is composed of 32 bits. These 32 bits are divided into 4
octets of 8 bits each. You may have seen an IP address represented like
this: 172.68.15.24. We must remember, however, that the computer understands
this number only in binary, so we must often deal with them in binary. Many
people are intimidated by this initially, but soon find that it is not
difficult. If you do not allow yourself to be flustered, you can master this
topic.

IP addresses are assigned to orginazations in blocks. Each block belongs to
one of three classes: class A, class B, or class C. You can tell what class
an IP address is by the value in its first octet.

Class A 1-126
Class B 128-191
Class C 192 --

An IP address consists of two fields. The first field identifies the
network, and the second field identifies the node on the network. Which bits
of the address are in the network field and which bits are in the host field
is determined by the subnet mask.

When a class A IP license is granted, you are assigned something like this:
99.0.0.0. Only the value of the bits in the first octet are assigned. This
means you are free to assign any values you wish in the second, third and
fourth octets.

The defualt subnet mask for a class A network is 255.0.0.0. High bits, ones,
indicate the bits that are part of the network field of the IP address. The
default subnet mask does not create subnets. Therefor, a class A network
with the default subnet mask is one network. The three octets that are
unassigned and unmasked are part of the host field of the address. There is
a total of 24 bits in those three octets. Each bit can be in one of two
states. Therefor, 2^24 is the number of host addresses that can be assigned
on that network, almost. Two addresses are reserved on every network,
x.x.x.0 and x.x.x.255. So the total number of hosts possible on this network
is 2^24. 2^24-2=16,777,214 hosts for a class A IP network.

When a class B license is granted, the first two octets are assigned. For
example, 172.198.x.x. The default subnet mask for a class B is 255.255.0.0.
One network, two octets free, 16 bits for the host address field.
2^16-2=65,534 possible host addresses on a class B IP network.

When a class C license is granted, the first three octets are assigned, for
example: 193.52.16.0. The default subnet mask for a class C is
255.255.255.0. Once octet makes up the host address field. 2^8-2=254 host
addresses possible on a class C network.

Thanks. I'm starting to get it. (Have no problems understanding bits -
used to program in Assembler)

Where is the class A defined: on workstation or router? Is it
something "in stone" or can I change it?

TIA, Eugene

My router (Linksys) IP is 192.168.1.1 and the worksation 192.168.1.101.
Then it should be class "C" - right?

Yes, it is.
"Eugene F." wrote in message
ups.com...
My router (Linksys) IP is 192.168.1.1 and the worksation 192.168.1.101.
Then it should be class "C" - right?

Yes, you can change it. You have to be careful, though. The subnet
determines what part of the address it "The Network", and what part
designates the hosts. You can have 2 PCs with similar IP addresses but, if
the subnets are different, they won't see each other because they would be
on different networks.

For example, using your address of 192.168.1.1, if the PC has a subnet of
255.255.255.0, then the network portion of the address is 192.168.1, and the
host portion is 1. If you have another PC with 192.168.1.2 with the subnet
of 255.255.0.0, it would NOT see the first PC, because it would be on
network 192.168 as host 1.1, and not compatible.

What would cause the subnet to spontaneously change, I don't have a clue.

"Eugene F." wrote in message
oups.com...
Thanks. I'm starting to get it. (Have no problems understanding bits -
used to program in Assembler)

Where is the class A defined: on workstation or router? Is it
something "in stone" or can I change it?

TIA, Eugene

HH,

I understand the basic idea of subnets.

What would cause the subnet to spontaneously change, I don't have a
clue.

Most unfortunately me too. Still in the dark.