Download Online IP CIDR / VLSM Supernet Calculator

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Route Calculator
CIDR Netmask
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0
CIDR Calculator
r
/
IP
CIDR Calculator
CIDR Calculator
IP Address
0 . 0
d
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0
Mask Bits
1
Maximum Subnets
2147483648
CIDR Network (Route)
0.0.0.0
128.0.0.0
Wildcard Mask
127.255.255.255
Maximum Addresses
2147483646
Net: CIDR Notation
0.0.0.0/1
CIDR Address Range
0.0.0.0 - 127.255.255.255
The CIDR Calculator enables CIDR network
calculations using IP address, CIDR mask (subnet
mask), mask bits, maximum required IP addresses and
maximum required subnets.
Results of the CIDR calculation provide the wildcard
mask, for use with ACL (Access Control Lists), CIDR
network address (CIDR route), network address in
CIDR notation and the CIDR address range for the
resulting CIDR network.
For classful subnets, please use the IP Subnet
Calculator. For classful supernets, please use the IP
Supernet Calculator. For simple ACL (Access Control
List) wildcard mask calculations, please use the ACL
Wildcard Mask Calculator.
CIDR - Classless Inter Domain Routing
CIDR - Classless Inter Domain Routing - was adopted to help ease
the load imposed on internet and large network backbone routers
by the increasing size of routing tables.
Large routing tables have several adverse effects:
Routers require more memory in order to store and
manipulate their routing tables which increases operation
costs.
Routing latency is increased due to the large amount of data
contained in the routing tables.
Network bandwidth usage is increased by routing updates
when routers exchange their routing tables.
A solution to these problems was found in CIDR. CIDR permits IP
Address aggregation which in turn reduces the size of routing tables
and so addresses the problems listed above.
CIDR and IP Address Aggregation
So what is IP Address Aggregation? Quite simply, IP Address Aggregation means that several networks can be spanned
by a single routing entry. Consider the following case:
Our router needs to route traffic for eight seperate networks through the same gateway (ip address 194.1.1.1):
ip
ip
ip
ip
ip
ip
ip
ip
route
route
route
route
route
route
route
route
66.100.50.0 255.255.255.224 194.1.1.1
66.100.50.32 255.255.255.224 194.1.1.1
66.100.50.64 255.255.255.224 194.1.1.1
66.100.50.96 255.255.255.224 194.1.1.1
66.100.50.128 255.255.255.224 194.1.1.1
66.100.50.160 255.255.255.224 194.1.1.1
66.100.50.192 255.255.255.224 194.1.1.1
66.100.50.224 255.255.255.224 194.1.1.1
Without CIDR, our routing table would need to maintain a seperate entry for each of the eight individual networks.
As the eight example networks are contiguous, i.e. their address spaces follow numerically with no gaps, we can
encapsulate all eight with a single CIDR route by simply changing the subnet mask:
ip route 66.100.50.0 255.255.255.0 194.1.1.1
It's easy to see the benefit of IP Address Aggregation and CIDR when we see the difference in routing table entries
between the "before CIDR" and "after CIDR" cases above. This is a very simple example but it is easy to imagine how
CIDR can help in the real world with much larger aggregations.
CIDR brings with it its own simplified form of IP network address notation. Instead of using the network address and
subnet mask, CIDR notation uses the network address followed by a slash ("/") and the number of mask bits. For
example, taking the CIDR network from the above case:
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66.100.50.0 255.255.255.0
would become
66.100.50.0/24
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