Subnet Calculator (IPv4 + IPv6)
Available Tools
1. subnet_calculator — IPv4 Subnet Details
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator '{"cidr":"192.168.1.0/24"}'Parameters:
cidr(required): IPv4 CIDR notation, e.g.,10.0.0.0/8,172.16.0.0/12,192.168.1.0/24
Returns:
- Network address, broadcast address, netmask, wildcard mask
- Prefix length, host bits
- Number of total and usable addresses
- First and last usable host addresses
- Usable hosts preview (up to 10)
- Previous and next subnets (same size)
- Address classification: private, global, link-local, multicast, loopback, reserved
- Human-readable summary
2. subnet_calculator_v6 — IPv6 Subnet Details
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator_v6 '{"cidr":"2001:db8::/48"}'Parameters:
cidr(required): IPv6 CIDR notation, e.g.,2001:db8::/32,fd00::/64,fe80::/10
Returns:
- Network address (compressed and exploded forms)
- Last address in range
- Prefix length, host bits
- Number of addresses (exact for /64+, exponential notation for larger)
- Number of /64 subnets contained
- Previous and next subnets
- Address classification: ULA, global unicast, link-local, multicast
- Standard allocation annotation (e.g., "/64 = SLAAC capable", "/48 = site allocation")
- Human-readable summary
3. subnet_calculator_auto — Auto-Detect IPv4/IPv6
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator_auto '{"cidr":"10.0.0.0/24"}'
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator_auto '{"cidr":"2001:db8:abcd::/48"}'Automatically detects IP version and calls the appropriate calculator.
When to Use
- Interface addressing: Calculate the correct subnet for a new interface
- VLSM planning: Break a large block into appropriately sized subnets
- ACL wildcard masks: Get the wildcard mask for access-list entries
- Routing verification: Confirm that route entries match expected subnets
- IPv6 migration planning: Understand IPv6 allocation standards (/48, /64, /128)
- Network design: Validate addressing schemes before deployment
- Troubleshooting: Verify if two IPs are in the same subnet
Common Network Engineering Scenarios
Scenario 1: Point-to-Point Link Addressing
IPv4 /30 link:
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator '{"cidr":"10.1.1.0/30"}'Result: 4 addresses, 2 usable (10.1.1.1 and 10.1.1.2). Standard for router-to-router links.
IPv4 /31 link (RFC 3021):
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator '{"cidr":"10.1.1.0/31"}'Result: 2 addresses (10.1.1.0 and 10.1.1.1). No broadcast waste.
IPv6 /127 link (RFC 6164):
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator_v6 '{"cidr":"2001:db8:1::/127"}'Result: 2 addresses. Recommended for IPv6 point-to-point links.
Scenario 2: VLSM Subnet Planning
Break 10.10.0.0/16 into subnets for different departments:
# Engineering: 500 hosts needed → /23 (510 usable)
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator '{"cidr":"10.10.0.0/23"}'
# Sales: 100 hosts needed → /25 (126 usable)
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator '{"cidr":"10.10.2.0/25"}'
# Management: 10 hosts needed → /28 (14 usable)
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator '{"cidr":"10.10.2.128/28"}'
# Server VLAN: 30 hosts needed → /27 (30 usable)
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator '{"cidr":"10.10.2.192/27"}'Produce an addressing plan:
Subnet Plan — 10.10.0.0/16
┌────────────┬─────────────────┬────────┬───────────┬───────────────┐
│ Department │ Subnet │ Prefix │ Usable │ Gateway │
├────────────┼─────────────────┼────────┼───────────┼───────────────┤
│ Engineering│ 10.10.0.0/23 │ /23 │ 510 hosts │ 10.10.0.1 │
│ Sales │ 10.10.2.0/25 │ /25 │ 126 hosts │ 10.10.2.1 │
│ Management │ 10.10.2.128/28 │ /28 │ 14 hosts │ 10.10.2.129 │
│ Servers │ 10.10.2.192/27 │ /27 │ 30 hosts │ 10.10.2.193 │
│ P2P Links │ 10.10.3.0/24 │ /30 ea │ 2 per link│ varies │
└────────────┴─────────────────┴────────┴───────────┴───────────────┘Scenario 3: IPv6 Site Allocation
Plan a /48 allocation for a campus:
# Site allocation
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator_v6 '{"cidr":"2001:db8:abcd::/48"}'
# Building 1 — first /56 from the /48
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator_v6 '{"cidr":"2001:db8:abcd::/56"}'
# Floor 1, Building 1 — first /64 from the /56
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator_v6 '{"cidr":"2001:db8:abcd::/64"}'
# Loopback /128
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator_v6 '{"cidr":"2001:db8:abcd::1/128"}'
# Point-to-point /127
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator_v6 '{"cidr":"2001:db8:abcd:ffff::/127"}'IPv6 Allocation — 2001:db8:abcd::/48
┌──────────────┬──────────────────────────┬────────┬──────────────────────┐
│ Purpose │ Prefix │ Size │ Note │
├──────────────┼──────────────────────────┼────────┼──────────────────────┤
│ Site │ 2001:db8:abcd::/48 │ /48 │ 65,536 /64 subnets │
│ Building 1 │ 2001:db8:abcd::/56 │ /56 │ 256 /64 subnets │
│ Floor 1/B1 │ 2001:db8:abcd::/64 │ /64 │ SLAAC capable │
│ Loopback │ 2001:db8:abcd::1/128 │ /128 │ Single host │
│ P2P Link │ 2001:db8:abcd:ffff::/127 │ /127 │ RFC 6164 │
└──────────────┴──────────────────────────┴────────┴──────────────────────┘Scenario 4: ACL Wildcard Mask Reference
# What's the wildcard for a /22?
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator '{"cidr":"10.0.0.0/22"}'Use the wildcard_mask field directly in ACL configuration:
ip access-list extended EXAMPLE
permit ip 10.0.0.0 0.0.3.255 anyScenario 5: Dual-Stack Verification
Verify both IPv4 and IPv6 assignments on an interface:
# IPv4 side
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator '{"cidr":"10.1.1.1/30"}'
# IPv6 side
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator_v6 '{"cidr":"2001:db8:1::1/127"}'Quick Reference: Common Prefix Sizes
IPv4
| Prefix | Hosts | Usable | Use Case |
|---|---|---|---|
| /30 | 4 | 2 | Point-to-point link |
| /29 | 8 | 6 | Small DMZ |
| /28 | 16 | 14 | Management VLAN |
| /27 | 32 | 30 | Server VLAN |
| /26 | 64 | 62 | Small department |
| /25 | 128 | 126 | Medium department |
| /24 | 256 | 254 | Standard subnet |
| /23 | 512 | 510 | Large subnet |
| /22 | 1024 | 1022 | Campus building |
| /16 | 65536 | 65534 | Campus site |
IPv6
| Prefix | Subnets (/64) | Use Case |
|---|---|---|
| /128 | 0 | Single host (loopback) |
| /127 | 0 | Point-to-point link (RFC 6164) |
| /64 | 1 | Standard subnet (SLAAC) |
| /56 | 256 | Building or floor |
| /48 | 65,536 | Site allocation |
| /32 | 16,777,216 | ISP allocation |
Integration with Network Config
After calculating subnets, use pyats-config-mgmt to apply:
# Calculate the subnet first
python3 $MCP_CALL "python3 -u $SUBNET_MCP_SCRIPT" subnet_calculator '{"cidr":"10.1.1.0/30"}'
# Then configure the interface
PYATS_TESTBED_PATH=$PYATS_TESTBED_PATH python3 $MCP_CALL "python3 -u $PYATS_MCP_SCRIPT" pyats_configure_device '{"device_name":"R1","config_commands":["interface GigabitEthernet2","ip address 10.1.1.1 255.255.255.252","no shutdown"]}'