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| monkeyboy 2001-05-23, 9:12 am |
| Say you were subnetting an IP address into 6 subnetworks - would you need a separate subnet mask for each? Is the subnet identifier the same as the subnet mask? | |
| strikeattack 2001-05-23, 9:21 am |
| You would use the same subnet mask for all 6 subnetworks, and no, the subnet identifier is not the same thing as the mask. In every subnetwork you have a subnet identifier and a broadcast address. This is why you have the minus two in the equation 2 to the Nth minus two.
A simple Class C Example:
192.168.001.000 network
255.255.255.000 subnet mask
192.168.001.000 is the subnetwork address.
192.168.001.255 is the broadcast address.
Hope this helps. | |
| monkeyboy 2001-05-23, 9:29 am |
| yeah - cheers for that - it's easy to get confused. so the only thing you manipulate is the IP address to define it's segment?
& once you've got your sn mask it's the same for the whole of the network | |
| strikeattack 2001-05-23, 9:35 am |
| It does not have to be the same for the entire internetwork, but it is the same for all nodes on that subnetwork. All nodes on a subnet will have the same subnet mask.
And, for clarification, you don't manipulate the IP address to define a segment, you change the IP address to define its HOST ID within that subnetwork. This is in comparison to the network ID, which falls directly above all the 1s in the subnet mask.
And, yes, it is easy to get confused. | |
| monkeyboy 2001-05-23, 9:56 am |
| so - going back to before - if I divide my IP address into subnetworks then the subnetworks/segments all share the same subnet mask? | |
| Trouble Man 2001-05-23, 10:21 am |
| quote:
so - going back to before - if I divide my IP address into subnetworks then the subnetworks/segments all share the same subnet mask?
Yes, unless you're using CIDR, which is not covered by the CCNA, but if you wanna know how CIDR works anyway, I'll send you an email w/attachments. | |
| monkeyboy 2001-05-23, 10:28 am |
| I get you now - & you only manipulate host part of id to define physical segment/ subnetwork (can these word be used interchangably) | |
| strikeattack 2001-05-23, 11:34 am |
| Trouble, Regarding this:
quote:
Yes, unless you're using CIDR, which is not covered by the CCNA, but if you wanna know how CIDR works anyway, I'll send you an email w/attachments.
Are you saying that if I combine multiple class C addresses into one supernetted subnet, the aggregated Class C subnets would all use a different mask? | |
| Trouble Man 2001-05-23, 11:52 am |
| I'll give an example of CIDR:
A warning for those studying for the CCNA test: This is not covered by the exam and might confuse the shit out of you so read with caution.
An ISP has a Class C network of 200.1.2.0 to lease out. Customer A needs 60 host address so the ISP gives them a subnet of 200.1.2.64 with a subnet mask of 255.255.255.192. This gives them a host range of 200.1.2.65-126, with the broadcast being 200.1.2.127.
Now Customer B asks the ISP for 30 addresses. The ISP doesn't want to give them a subnet of 200.1.2.128 with a mask of 255.255.255.192, because that would waste 32 addresses. With CIDR it can give them a subnet of 200.1.2.32 with a mask of 255.255.255.224, and the host range is 200.1.2.33-62 (broadcast 63). See how the same network can be broken into different subnets with different subnet masks.
Also with CIDR you can have Class C's act as A's and B's. and B's act as A's. I won't go into that here. If you want to know more, e-mail me and I'll send you a small class on it. | |
| strikeattack 2001-05-23, 12:17 pm |
| No, I understand all that. It just sounded from your post that a single ISP would have more than one mask to deal with, and thats the part that I did not agree with.
Just for clarification for those reading this: If CIDR did not have to work on binary boundaries, it would be able to combine addresses more efficently. However, because it uses powers of two (binary boundaries), it is rare that an ISP will be able to give a subnet mask that will FIT EXACTLY with what the requirements are. | |
| Trouble Man 2001-05-23, 1:32 pm |
| I see: I misunderstood your question to my answer to his question which was an aside to your answer to his question.
No problem | |
| Yankee 2001-05-24, 3:30 am |
| Me thinks what Strike is accurately pointing out is that the binary system causes some "wasted" IPs in many instances. That's why ISPs love giving out just one IP per account 
Yankee |
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