shaheen@cs.odu.edu (Rafat Y. Shaheen) (06/15/90)
Robert W. (Bob) Hott writes: > > I have a quick question, hopefully you will not flame to loudly with > regard to viewing RFCs. I looked through RFC 950 to try to determine > how to specify a host when using a subnet. In my particular instance we > have a class B network. I am interested in how one would specify > addresses when a subnet of 6 bits is used. > > Suppose I want the 300th host on the 1 subnet of a class B network with > a netmask of 255.255.252! Should I specify the IP address as > 128.38.1.300 or 128.38.253.44 > > I guess my overall question is: Should I specify the addressing using > the 3rd octet field in the dot notation as the subnet or as the 3rd > octet of the 32 bit field? Bob: With all the ansewrs I have' read so far, only one answer looks allright: It was from Michael.E.Pare mep@aqua.whoi.edu. The following is to confirm: To get things straight now: You want to have 6 bits for a subnet: Your mask is : 255.255.252.0 And you can address up to 2**6 = 63 physical network And up to 2**10 = 1023 hosts within one such network. You declared the first 6 bits of the third octet to be the physical nets: 11111111|11111111|11111100|00000000 <---- Subnet Mask The first subnet will be to set the first bit in the physical net address, which is the third position from the right in the third octet, that is: 10000000|00100110|00000100|00000001 This correspond to: 128.38.4.1 <-----For the 1st host in the 1st subnet. and for the 300th host: 10000000|00100110|00000101|00101100 Which corresponds to: 128.38.5.44 <---- Same answer as Michael Another example, for the second subnet and the 300th host: 10000000|00100110|00001001|00101100 Which corresponds to: 128.38.9.44 References: [1] InterNetworking with TCP/IP, Douglas Comer (Purdu University),1988 RFCs: The standard for subnet addressing comes from Mogul[RFC 950]; Clark [RFC 932], Karels [RFC 936], Gads [RFC 940], and Mogul[RFC 917] All contain early proposals for subnet addressing schemes. Mogul[RFC 932] discusses broadcasting in the presence of subnets. Postel [RFC 925] considers the use of proxy ARP for subnets. Carl-Mitchell and Quarterman [RFC 1027] discusses using proxy ARP to implement transparent subnet gateways. Best Regards. ... Shaheen Old Dominion University (ODU) Rafat Y. Shaheen shaheen@cs.odu.edu