Reserved addresses in subnet & Number of subnets
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From: karthikbalaguru on 10 Jan 2010 21:17 Hi, In Class B Subnetting, 1. Consider that the subnet mask is 255.255.192.0 then, the number of hosts is 16382. The number of subnets is 2. 2. Similarly for the subnet mask of 255.255.224.0, the number of hosts is 8190. The number of subnets is 6. I understand that the reasons for 16382 and 8190 is that the first(all zeros) and the last addresses(all ones) have been reserved in every subnet due to historical reasons. Can you lemme know the historical reason ? I searched the internet, but did not find info except for some links mentioning the term 'historical reasons'. Further, shouldn't the number of subnets be 4 for the first scenario and 8 for the second scenario ? Any specific reasons for not using subnet-zero(all-zeros subnet) and all-ones-subnet ? Thx in advans, Karthik Balaguru
From: karthikbalaguru on 10 Jan 2010 21:40 On Jan 11, 7:17 am, karthikbalaguru <karthikbalagur...(a)gmail.com> wrote: > Hi, > In Class B Subnetting, > 1. Consider that the subnet mask is 255.255.192.0 > then, the number of hosts is 16382. The number of > subnets is 2. > 2. Similarly for the subnet mask of 255.255.224.0, > the number of hosts is 8190. The number of > subnets is 6. > > I understand that the reasons for 16382 and > 8190 is that the first(all zeros) and the last > addresses(all ones) have been reserved in > every subnet due to historical reasons. > Can you lemme know the historical reason ? > I searched the internet, but did not find info > except for some links mentioning the term > 'historical reasons'. > > Further, shouldn't the number of subnets be > 4 for the first scenario and 8 for the second > scenario ? Any specific reasons for not using > subnet-zero(all-zeros subnet) and > all-ones-subnet ? > On further seraching in internet, i got the below link throws some light on it, but not very explicitly - http://en.wikipedia.org/wiki/Subnetwork#Subnet_zero_and_the_all-ones_subnet It seems to convey that RFC 950 prohibits the usage while RFC 1878 allows the usage. I do find the below statement in RFC 1878, " This practice is obsolete! Modern software will be able to utilize all definable networks. " Eager to know the method followed by modern softwares to utilize all the definable networks. Why was it a problem earlier ? Any ideas ? Thx in advans, Karthik Balaguru
From: unruh on 10 Jan 2010 23:56 ["Followup-To:" header set to comp.os.linux.networking.] On 2010-01-11, karthikbalaguru <karthikbalaguru79(a)gmail.com> wrote: > Hi, > In Class B Subnetting, > 1. Consider that the subnet mask is 255.255.192.0 > then, the number of hosts is 16382. The number of > subnets is 2. ??? There can be almost any number of subnets, as I understand it. Subnets are not limited to groups of 256 addresses. > 2. Similarly for the subnet mask of 255.255.224.0, > the number of hosts is 8190. The number of > subnets is 6. > > I understand that the reasons for 16382 and > 8190 is that the first(all zeros) and the last > addresses(all ones) have been reserved in > every subnet due to historical reasons. > Can you lemme know the historical reason ? > I searched the internet, but did not find info > except for some links mentioning the term > 'historical reasons'. broadcast > > Further, shouldn't the number of subnets be > 4 for the first scenario and 8 for the second > scenario ? Any specific reasons for not using > subnet-zero(all-zeros subnet) and > all-ones-subnet ? > > Thx in advans, > Karthik Balaguru
From: samhas on 11 Jan 2010 02:53 > Eager to know the method followed by > modern softwares to utilize all the > definable networks. Why was it a problem > earlier ? I think you are confusing two things: classless vs. classful interdomain routing and subnets. In the beginning of the global internet the ip address space was separated in several address classes e.g. class A (having 3 bytes for host addressing), class B (2 bytes), class C (1 byte), etc.. The problem with that: you only have a very limited number of class A networks with too many host addresses (2^24 - 2). So the internet community switched to classless interdomain routing, that means you can cut the ip address at any position to seperated net- and host-part. This is now applicable for global routing, too. But for you as an organisation it was always possible to build some subnets within your address space. hth samhas
From: karthikbalaguru on 11 Jan 2010 10:58
On Jan 11, 9:56 am, unruh <un...(a)wormhole.physics.ubc.ca> wrote: > ["Followup-To:" header set to comp.os.linux.networking.] > On 2010-01-11, karthikbalaguru <karthikbalagur...(a)gmail.com> wrote: > > > Hi, > > In Class B Subnetting, > > 1. Consider that the subnet mask is 255.255.192.0 > > then, the number of hosts is 16382. The number of > > subnets is 2. > > ??? There can be almost any number of subnets, as I understand it. > Subnets are not limited to groups of 256 addresses. > I think, the below link also seems to convey 2 subnets if subnet mask is 255.255.192.0 - http://www.networkcomputing.com/unixworld/tutorial/001.html > > 2. Similarly for the subnet mask of 255.255.224.0, > > the number of hosts is 8190. The number of > > subnets is 6. > > > I understand that the reasons for 16382 and > > 8190 is that the first(all zeros) and the last > > addresses(all ones) have been reserved in > > every subnet due to historical reasons. > > Can you lemme know the historical reason ? > > I searched the internet, but did not find info > > except for some links mentioning the term > > 'historical reasons'. > > broadcast > > Thx for your inputs ! http://en.wikipedia.org/wiki/Subnetwork#Subnet_zero_and_the_all-ones_subnet The above link conveys some clear info. The remaining bits after the subnet are used for addressing hosts within the subnet.In the various configurations for the host identifier, the all zeros value and all ones value are reserved for the network ID and broadcast address respectively. So,the number of available hosts on a subnet is (2 to the powerof n) - 2, where n is the number of bits used for the host portion of the address except while dealing with 31-bit subnet masks where network and broadcast addresses is not necessary (RFC 3021). > > > Further, shouldn't the number of subnets be > > 4 for the first scenario and 8 for the second > > scenario ? Any specific reasons for not using > > subnet-zero(all-zeros subnet) and > > all-ones-subnet ? > The same link also conveys the below - - Problem in using subnet zero - confusion created by having a network and subnet with the same address. - Problem if subnetting has all bits in the subnet bit group set to one - Possible confusion with the broadcast address. Thx, Karthik Balaguru |