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Q: Five-octet network ID's ( Answered,   1 Comment )
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 Subject: Five-octet network ID's Category: Computers > Internet Asked by: idunnoman-ga List Price: \$15.00 Posted: 12 Nov 2006 09:21 PST Expires: 12 Dec 2006 09:21 PST Question ID: 782103
 ```I am studying for my MCSE and have noticed in the study materials that it mentions network ID's containing five subnets. (e.g. 207.206.64.1.19) I am not familiar with this convention and don't know what it's used for. I am used to regular old IP addresses with four subnets. An explanation would be great.``` Request for Question Clarification by sublime1-ga on 12 Nov 2006 12:31 PST ```idunnoman... I'm wondering if you're seeing the word 'subnet' and understanding it to mean a fifth decimal section (octet) in the IP address, or do the study materials actually contain an address such as the example you've given (207.206.64.1.19)? If no such example was given, I think you're misunderstanding the word subnet. The 4 sections of the IP address are called 'octets', from their derivation from binary math. 'Subnets' refer to a portion of an IP network defined by a subnet mask. Devices on the same subnet have the same subnet mask. An informative discussion of all of this is provided in this question posted by bagelboy and the answers given on the MCSE forum on the VelocityReviews site: "For a class C network, a subnet mask of 255.255.255.224 (binary 11111111 11111111 11111111 11100000) indicates that the first three octets and the first 3 bits [digits] of the last octet identify the subnetted network ID. The remaining 5 bits identify the hosts on that subnet. Because 3 bits are used to define the subnetting structure of this class C network, the network will support up to 8 subnets and up to 30 hosts per subnet." More on the page: http://www.velocityreviews.com/forums/t52742-calculating-subnet-hosts.html Let me know if this satisfies your interests... sublime1-ga```
 ```Hello idunnoman, Thank you for your question. I feel absolutely certain that I know exactly what you are referring to. You are talking about the short hand notation of Network + host address with subnet identifiers. For example: 192.168.254.1/24 means the subnet mask of 255.255.255.0 This gives you one subnet on the network with a network address of 192.168.254.0 and a broadcast address of 192.168.254.255 The notation shown as 192.168.254.1/26 means your subnet mask is shown as 255.255.255.192 This gives you a network address of 192.168.254.64 and a broadcast address of 192.168.254.127, also a network address of 192.168.254.128 with a broadcast address of 192.168.254.191, also a network address of 192.168.254.192 and a broadcast address of 192.168.254.255. Remember that Microsoft does not accept subnet zero! Things get a lot hairier when you get into supernets. I will let you find that out for yourself. The final number in that 5 octet address just defines the number of bits used for the network MASK of the IP ADDRESS that is borrowed from the host identifier and from there you can work out the bits used for the host identifiers. I have to admit that I got a little stuck with this but I kept with it and it became clear at the end. What books are you reading? I would really advise you to read the MSPRESS 70-291 and 70-293 books dedicated to the MCSE syllabus. They are by far the best books I read pertaining to the MCSE and you will not go wrong with them. Let me know if you need any additional clarification and I'll be glad to assist you. --keystroke-ga``` Clarification of Answer by keystroke-ga on 12 Nov 2006 18:18 PST ```This is also known as Classless InterDomain Routing or CIDR. This webpage will really help you out with the understanding. Wikipedia Entry-- Classless Inter-Domain Routing http://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing --keystroke-ga```
 `Maybe he means the MAC address`