The system may support what is called an "ICMP Netmask" request where you
can send a specific ICMP packet to the host and it will respond with its
netmask in another ICMP packet. You can do the same to find the remote
time on the machine ("ICMP Timestamp" request) too.
A program called SING (Send ICMP Nasty Garbage) is available at
http://sourceforge.net/projects/sing/ that can send all kinds of ICMP
messages and may be able to retrieve this information from the
host.
-Jason
On Mon, 9 Oct 2000, Hafida Fouta wrote:
> Date: Mon, 9 Oct 2000 14:52:55 +0000 (GMT)
> From: Hafida Fouta <[EMAIL PROTECTED]>
> To: [EMAIL PROTECTED]
> Cc: [EMAIL PROTECTED]
> Subject: Re: Subnet mask
>
>
> 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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>
--
AT&T Wireless Services
IT Security
UNIX Security Operations Specialist
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