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c i Subnets CIDR Wildcard Feedback Ads by Google IP Address Usage Route Calculator CIDR Netmask . 0 CIDR Calculator r / IP CIDR Calculator CIDR Calculator IP Address 0 . 0 d . 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: converted by Web2PDFConvert.com 66.100.50.0 255.255.255.0 would become 66.100.50.0/24 converted by Web2PDFConvert.com converted by Web2PDFConvert.com