Notación CIDRCIDR
What is CIDR notation?
Classless Inter-Domain Routing format indicating leading network mask bits (e.g., /24 equals 255.255.255.0, designating a 256-address block).
NETWORKING & IP CONNECTIVITY
Calculator of IP Subnets & Network Planner
Calculate IPv4/IPv6 subnets, plan IPs by device type and download Excel inventory.
A/B/C are mask shortcuts (/8, /16, /24). Offices usually use C · /24.
IP planner (IPv4)
Pick networks → Auto or manual range → colored Excel (free IPs summarized if many).
Networks in the plan
Check networks to plan.
Calculate an IPv4 network above.
Select at least one network to configure categories.
IP Subnetting Architecture & CIDR
Subnet masks, binary host/network math, RFC 1918 private ranges, and IPv6.
CIDR Fundamentals & Network Splitting
CIDR replaced rigid Class A/B/C addressing. The prefix (/24, /16) denotes the contiguous network bits, allocating the remainder for host addresses.
RFC 1918 Private Ranges & NAT
Ranges 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 are non-routable over the internet, relying on NAT gateways to access public services.
Subnet Mask vs. Wildcard Mask (ACLs)
The subnet mask filters the network portion via bitwise AND. The wildcard mask (inverse of mask) is essential for Cisco Access Control Lists (ACLs) and OSPF.
IPv6 Address Space & Standard /64 Subnets
IPv6 uses 128-bit hexadecimal addressing. Standard local LAN allocations use /64 prefixes, granting 18.4 quintillion addresses per subnet for SLAAC autoconfig.
IP Subnetting & Routing Troubleshooting
Step-by-step fixes for IP conflicts, unreachable gateways, and DHCP pool shortages.
Issue 1
Duplicate IP Address Conflict in Local LAN
⚡ Quick Fix:Run `ipconfig /release && ipconfig /renew` to request a fresh, uncontested lease from DHCP.
🔧 Technical Fix:Reserve static IPs (.1 to .50) outside the active DHCP allocation pool range (.51 to .254) in router settings.
Issue 2
Default Gateway Outside Subnet Boundary
⚡ Quick Fix:Verify both host IP and gateway IP fall within the exact same CIDR boundary.
🔧 Technical Fix:Set gateway to a valid usable host (typically first .1 or last .254), never the network (.0) or broadcast (.255).
Issue 3
DHCP Pool Exhaustion in /24 Subnets
⚡ Quick Fix:Lower DHCP lease time from 24h to 2h to quickly reclaim addresses from transient guest devices.
🔧 Technical Fix:Expand subnet mask from /24 (254 hosts) to /23 (510 hosts, 255.255.254.0) or /22 (1022 hosts, 255.255.252.0).
Issue 4
Inter-VLAN Communication Breakdown
⚡ Quick Fix:Ping the local VLAN gateway to verify Layer 3 switch virtual interfaces (SVI) are up.
🔧 Technical Fix:Enable `ip routing` on Layer 3 switches or configure 802.1Q subinterfaces on the core firewall.
Did You Know? IP Subnetting Trivia
IPv4 exhaustion history, IPv6 cosmic scale, and the 127.0.0.1 loopback origin.
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February 3, 2011: IPv4 Pool Exhaustion
On this date, IANA allocated the final five /8 blocks (16.7M IPs each) to regional registries, formally exhausting global unallocated IPv4 space.
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340 Undecillion IPv6 Addresses (3.4 × 10^38)
IPv6 provides 3.4 × 10^38 addresses. There are enough IPs to assign trillions of addresses to every grain of sand on planet Earth.
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127.0.0.1: Why 16 Million IPs Were Reserved for Localhost
In 1981, RFC 790 reserved the entire 127.0.0.0/8 block (16.7M addresses) for internal loopback. Any address like 127.0.0.2 routes right back to localhost.
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Why We Subtract 2 (Network & Broadcast)
In every IPv4 subnet, all-zeros host bits designate the network ID and all-ones host bits designate the broadcast address, requiring (2^n - 2) usable hosts.
Subnetting Architecture & CIDR Masks Glossary
Learn the fundamental concepts, protocols, and technical terminology of this tool.
Dirección de BroadcastIPv4
What is a subnet Broadcast address?
The final address in an IPv4 subnet block reserved for broadcasting packets simultaneously to every connected host within that network broadcast domain.
Dirección de RedIPv4
What is a Network ID address?
The base address identifying the subnet where all host bits are zero, used by routing tables and unavailable for host device assignment.
Máscara WildcardRouting
What is a Wildcard mask?
The inverted binary complement of a subnet mask (e.g., 0.0.0.255), heavily utilized in Cisco IOS routing filters and Access Control Lists (ACLs).