I know that this is pretty basic information but I having a problem trying to figure it out. I have run across a configuration issue on my vpn concentrator where I should put in the network list addresses that include the subnet and wildcard mask. Will some explain what is meat by a SUBNET MASK. Thanks.
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Subnet Wildcard Question
- Thread starter JRMS
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simply put, a subnet mask is an indicator to separate subnetwork and its host.
for an example, you have a class A network: 1.0.0.0
the default mask is 255.0.0.0
which means, the first octet (8 bits) is the network bits and the next 3 octets are (24 bits) host bits.
the network bits u cannot control. the host bits however, u can manupulate them to suit your need.
given the fact u have 24 bits -> 2^24 - 2 = number of hosts in a network.
but seriously, who has 16777214 PCs hooked up on their LAN? Not only LAN has its host limit but too many packet collision would make the network fail all the time.
To rectify the possible problem, you need to create subnetworks.
Simply put, subnetwork is network within a network.
with the network address 1.0.0.0, if one needs around 253 additional networks you would use the 2nd octets.
with that, each subnet still have 2^16-2 host available.
1.0.0.0 -> mask -> 255.0.0.0
1.0.0.0 -> 253 network = subnet mask -> 255.255.0.0
given the subnet mask 255.255.0.0
"255" portion is the network portion (whereas all binary bits equal to "1")
"0" portion is the host portion (whereas all binary bits equal to "0").
the network and subnet portion is masked out by using the binary value "1" to its network bit.
i hope i have made this clear.
Microbyte
![[medal]](/data/assets/smilies/medal.gif "[medal] [medal]")
for an example, you have a class A network: 1.0.0.0
the default mask is 255.0.0.0
which means, the first octet (8 bits) is the network bits and the next 3 octets are (24 bits) host bits.
the network bits u cannot control. the host bits however, u can manupulate them to suit your need.
given the fact u have 24 bits -> 2^24 - 2 = number of hosts in a network.
but seriously, who has 16777214 PCs hooked up on their LAN? Not only LAN has its host limit but too many packet collision would make the network fail all the time.
To rectify the possible problem, you need to create subnetworks.
Simply put, subnetwork is network within a network.
with the network address 1.0.0.0, if one needs around 253 additional networks you would use the 2nd octets.
with that, each subnet still have 2^16-2 host available.
1.0.0.0 -> mask -> 255.0.0.0
1.0.0.0 -> 253 network = subnet mask -> 255.255.0.0
given the subnet mask 255.255.0.0
"255" portion is the network portion (whereas all binary bits equal to "1")
"0" portion is the host portion (whereas all binary bits equal to "0").
the network and subnet portion is masked out by using the binary value "1" to its network bit.
i hope i have made this clear.
Microbyte
Subnet masks and Wildcard masks are essentially opposites. Where subnet masks use 1's to indicate the network portion, wildcards use 0's.
To specify the subnet mask for the 192.168.2.0 network (default class), you'd use 255.255.255.0 as Microbyte indicated.
To specify the wildcard for the same network, use 0.0.0.255.
Whether you need subnets or wildcards depends upon your equipment. IOS-based routers use wildcards, the Pix (FOS) uses subnet masks. I'm not sure, but I think the VPN concentrator uses subnets also.
To specify the subnet mask for the 192.168.2.0 network (default class), you'd use 255.255.255.0 as Microbyte indicated.
To specify the wildcard for the same network, use 0.0.0.255.
Whether you need subnets or wildcards depends upon your equipment. IOS-based routers use wildcards, the Pix (FOS) uses subnet masks. I'm not sure, but I think the VPN concentrator uses subnets also.
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