Vslm
- Thread starter Heather
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Harold III
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when you turn classless on, the routing protocol that supports classless will send subnet mask information in the routing messages/updates/whatever. Therefore if your router interface has a subnet address, and two other routers connecting to this interface, they can have different subnet masks. 192.168.1.64/26 has two available subnets, you can further divide the subnet 192.168.1.64/26 into 2 more subnets: 192.168.1.208/28 and 192.168.1.224/28
mikesgroovin
HONK if you route packets
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Heather, does this make sense?
I have to admit.....I might have explained it in the same fashion. But If you dont understand.....we can try to explain a little better.
-Mike
I have to admit.....I might have explained it in the same fashion. But If you dont understand.....we can try to explain a little better.
-Mike
Harold III
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It's been a long time since Heather posted this thread so I don't think Heather is still browsing the forum.
thanks so much Harold III for trying to help, yes I've been out of touch, had finals and stuff going on. You know how it is when you're taking cisco!!!!!!!!!
The main problem I am having with the whole concept is how do you know what subnet mask to give the new subnet when using vlsm? how do you figure the range of addresses?
yours truley,
daised and confused,
Heather
The main problem I am having with the whole concept is how do you know what subnet mask to give the new subnet when using vlsm? how do you figure the range of addresses?
yours truley,
daised and confused,
Heather
Harold III
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- 333
In vlsm you just borrow bits from the parent subnet mask as you did in traditional subnetting. For example,
the parent network is 192.168.1.64/255.255.255.192
there are 2 bits in the last octet of the subnetmask turned on. If you want, say, 5 subnets. 2^3-2=6>5, then you need to borrow 3 bits from the host portion and get 255.255.255.248
since subnet mask information is sent with the network number of each route, the routing protocol compares the new subnet mask with that of the parent network number, rather than a default subnet mask of classes (like, in non-vlsm protocols, if a router see 10 as the first octet of an IP address, its subnet mask will automatically be 255.0.0.0)
The range of the new address is, you have 6 available subnets, with 6 hosts in each subnet. the first subnet will be 192.168.1.200 because in its parent subnet mask shown below, any bit in the bold portion can be turned on and 001 is the smallest number (can't be all turned off):
parent subnet mask: 11111111.11111111.11111111.11000000
parent IP address: 11000000.10101000.00000001.01000000
New subnet mask: 11111111.11111111.11111111.11111000
New Ip address: 11000000.10101000.00000001.01001000
And then you can just add 8 to each subnet address to get the next subnet address. add 1 to get the first host address and add 7 to get broadcast address. you can get the last subnet address by turning on all the bits in the bold portion except the last one on the right. In this case, it is 11000000.10101000.00000001.01110000
the parent network is 192.168.1.64/255.255.255.192
there are 2 bits in the last octet of the subnetmask turned on. If you want, say, 5 subnets. 2^3-2=6>5, then you need to borrow 3 bits from the host portion and get 255.255.255.248
since subnet mask information is sent with the network number of each route, the routing protocol compares the new subnet mask with that of the parent network number, rather than a default subnet mask of classes (like, in non-vlsm protocols, if a router see 10 as the first octet of an IP address, its subnet mask will automatically be 255.0.0.0)
The range of the new address is, you have 6 available subnets, with 6 hosts in each subnet. the first subnet will be 192.168.1.200 because in its parent subnet mask shown below, any bit in the bold portion can be turned on and 001 is the smallest number (can't be all turned off):
parent subnet mask: 11111111.11111111.11111111.11000000
parent IP address: 11000000.10101000.00000001.01000000
New subnet mask: 11111111.11111111.11111111.11111000
New Ip address: 11000000.10101000.00000001.01001000
And then you can just add 8 to each subnet address to get the next subnet address. add 1 to get the first host address and add 7 to get broadcast address. you can get the last subnet address by turning on all the bits in the bold portion except the last one on the right. In this case, it is 11000000.10101000.00000001.01110000
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