subnet
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... network names,
addresses, and subnets, as well as an instance of the general method
for mapping between allocated network ...
... network name
syntax, the mappings to be provided, and possible support for similar
functions at the subnet level.
...
... Similar mappings for subnets, even when nested. ...
...
The primary application is to be able to identify all of the
subnets involved in a particular IP address. A secondary
requirement ...
...
The main advantage of this scheme over the first is that it
allows convenient names for subnets as well as networks. A
secondary advantage is that it uses names which are not in use
...
... host-zero IP
addresses. The same method is used for subnets in a nested
fashion. For example, 0.0.0.10.IN-ADDR.ARPA. for net 10.
...
... RRs, which
are present if the network (or subnet) is subnetted further.
If a type A RR is present, then it has the address ...
... ARPANET is a Class A network without subnets. The RRs which
would be added, assuming the ARPANET ...
... class B number. Suppose the ISI network
was organized into two levels of subnet, with the first level using
an additional 8 bits of address ...
... subnet.isi.edu. PTR 0.1.9.128.IN-ADDR.ARPA.
div2-subnet.isi.edu. PTR 0.2.9.128.IN-ADDR.ARPA.
...
... IN-ADDR.ARPA.
; Define second level subnets
inc-subsubnet.isi.edu. PTR 16.2.9.128.IN-ADDR.ARPA.
...
... A 255.255.255.0 ;aka X'FFFFFF00'
; Define one of the first level subnet numbers and masks
0.1.9.128.IN-ADDR.ARPA. PTR div1-subnet ...
... subnet numbers and masks
0.1.9.128.IN-ADDR.ARPA. PTR div1-subnet.isi.edu.
A 255.255.255.240 ;aka X'FFFFFFF0'
...
... A 255.255.255.240 ;aka X'FFFFFFF0'
; Define another first level subnet number and mask
0.2.9.128.IN-ADDR.ARPA. PTR div2-subnet ...
... subnet number and mask
0.2.9.128.IN-ADDR.ARPA. PTR div2-subnet.isi.edu.
A 255.255.255.240 ;aka X'FFFFFFF0'
...
... A 255.255.255.240 ;aka X'FFFFFFF0'
; Define second level subnet number
16.2.9.128.IN-ADDR.ARPA. PTR inc-subsubnet.isi.edu.
...
... This assumes that the ISI network is named isi-net.isi.edu., first
level subnets are named div1-subnet.isi.edu. and div2-
subnet ...
... network is named isi-net.isi.edu., first
level subnets are named div1-subnet.isi.edu. and div2-
subnet.isi.edu., and a second level subnet ...
... subnets are named div1-subnet.isi.edu. and div2-
subnet.isi.edu., and a second level subnet is called inc-
subsubnet.isi.edu. (In a real system as complicated as this there
...
... subnet.isi.edu. and div2-
subnet.isi.edu., and a second level subnet is called inc-
subsubnet.isi.edu. (In a real system as complicated as this there
would be more first and second level subnets ...
... subnet is called inc-
subsubnet.isi.edu. (In a real system as complicated as this there
would be more first and second level subnets defined, but we have
shown enough to illustrate the ideas.)
...
... Procedure for finding all subnets involved with an IP address ...
... RR.
If the A RR is found, look up the next level of subnet using the
original IP address and the mask in the A RR ...
...
0.2.9.128.IN-ADDR.ARPA. PTR div2-subnet.isi.edu.
A 255.255.255.240
...