Yes, What I wanted to say is that I know the IP address of a host. How
can I communicate with this host to get its subnet mask. I know that it is
using row sockets and ICMP packets but I don't know how?
On Mon, 9 Oct 2000 [EMAIL PROTECTED] wrote:
>
> #I have the IP address of a host and I want to get its subnet mask
> #can any one tell me how I can do this?
>
> I got the following information off of the Cisco website a while ago (I
> think). The IP address alone no longer gives you the netmask because of
> CIDR. Any IP address can have a number of different netmasks depending on
> how the network engineers are divvying up the network.
>
> Regards,
> Jeffery Gieser
>
>
> Netmasks and Netblock Sizes
>
> Netblock Sizes, Netmasks, and Bit-sized Networks
> The following table shows the relationship between IP network's block
> sizes, classful interpretation, netmasks, "supernets" [bit-length], "cisco
> wild bits" and the actual bit-sizes of the networks.
>
>
> An IP address on its own does not communicate what size network block to
> which it belongs. A netmask associated with an IP address describes
> "masked" portions [the left-most bits 'blocked out' by the ones in the
> netmask] of an IP address. These masked portions create the "network part"
> of the address, commonly called the "prefix".
>
> Block Size
> The block size tells you how many addresses are within the network. The
> "bottom" [all-zero] is reserved to refer to the network itself and "top"
> [all-ones] is reserved as the broadcast address, so these are unusable.
> therefore, any given netblock has two less usable addresses that the
> literal block size.
>
>
> Eg, a network 10.0.0.64 with a block size of four has only two usable
> addresses, 10.0.0.65 and 10.0.0.66.
>
> Netmask
> The netmask indicates the final (or final two) octets of what should be
> masked against the address to configure equipment or define routes with the
> apropriately-sized network. All leading [leftmost] octets in a netmask are
> ones.
>
>
> Eg, a network 10.0.16.0 with a netmask of 252.0 would result in a network
> netmask pair of 10.0.16.0 255.255.252.0, while the previous example from
> block size would result in 10.0.0.64 255.255.255.252.
> Cisco "Wild Bits"
> The cisco wild bits indicate the apropos value for the final (or final two)
> octets of what is needed when creating a Cisco router's access list for a
> certain network size. It is one less than the block size, merely because
> given the network number [the "zero" or "bottom" of the network], the "wild
> bits" define all the remaining possible values within the network.
>
> "Supernet"
> The supernet notation indicates the literal bitsize of a network.
> "Supernet" is actually a misnomer, stemming from the perceived need to
> differentiate prefixes longer than 24-bits [subnets of "Class C" blocks]
> from those shorter than 24-bits in traditional "Class C space" (eg, the
> 207.* network), calling ther latter "supernets". The number actually
> represents the "prefix length" - what part of an address is the
> network-part.
>
>
> Given that IPv4 addresses are 32-bits long, this is the most common and
> easy way of describing a network. A network of one device (a host route) is
> defined as easily as a network of two hundred fifty-six devices:
> 10.0.99.99/32 is a host and 10.0.98.0/24 is a "C-sized block".
>
>
> This notation is the UltraNet standard for describing network sizes.
>
> Raw Bits
> The raw bits define the bits "within" the network. These are the inverse of
> the supernet notation, and are a bitwise representation of the blocksize.
> Lastly, this is the exponent for "2" when describing the network
> mathematically.
>
> Classful
> The classful row merely gives a "backwards compatible" reference. All
> classful interpretations [Class A, B, C, D and E networks] of IPv4 space
> are archaic. This row is provided to give a reference point when speaking
> to customers that do not yet have a firm grasp of "supernet" notation.
>
> Reference Table
> Netmasks and Wild Bits refer to the RIGHTMOST octets.
>
>
> block size 1 2 4 8 16 32 64 128 256
> netmask 255 254 252 248 240 224 192 128 0
> cisco wild bits 0 1 3 7 15 31 63 127 255
> supernet /32 /31 /30 /29 /28 /27 /26 /25 /24
> raw bits 0 1 2 3 4 5 6 7 8
> Classful |------ Subnets of Class C addresses ------|
>
>
> block size 512 1024 2048 4096 8192 16384 32768
> netmask 254.0 252.0 248.0 240.0 224.0 192.0
> 128.0
> cisco wild bits 1.255 3.255 7.255 15.255 31.255
> 63.255 127.255
> supernet /23 /22 /21 /20 /19 /18 /17
> raw bits 9 10 11 12 13 14 15
>
> Classful |--------- Subnets of Class B addresses --------|
>
>
> block size 65536
> netmask 0.0
> cisco wild bits 255.255
> supernet /16
> raw bits 16
> Classful Class B
>
>
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