Chris SerenoTable of Contents
Packet Structure
| Version | Header Length | ToS/DSCP | Total Length | |
| Identification | Flags | Fragment Offset | ||
| TTL | Protocol | Header Checksum | ||
| Source Address | ||||
| Dest Address | ||||
| Options | Padding | |||
| Data |
IP Classes and Ranges
| Class | CIDR | Subnet Mask | IP Range | Description |
|---|---|---|---|---|
| A | 0.0.0.0/1 | 128.0.0.0 | 0.0.0.0 - 127.255.255.255 | Classful class A address space |
| 10.0.0.0/8 | 255.0.0.0 | 10.0.0.0 – 10.255.255.255 | Private class A addressing | |
| 127.0.0.0/8 | 255.0.0.0 | 127.0.0.0 - 127.255.255.255 | Used for loopback addresses (localhost) | |
| B | 128.0.0.0/1 | 128.0.0.0 | 128.0.0.0 - 191.255.255.255 | Classful class B address space |
| 169.254.0.0/16 | 255.255.0.0 | 169.254.0.0 - 169.254.255.255 | local link address | |
| 172.16.0.0/12 | 255.240.0.0 | 172.16.0.0 – 172.31.255.255 | Private class B addressing | |
| C | 192.0.0.0/1 | 128.0.0.0 | 192.0.0.0 - 223.255.255.255 | Classful class C address space |
| 192.0.2.0/24 | 255.255.255.0 | 192.0.2.0 - 192.0.2.255 | Used for documentation | |
| 192.168.0.0/16 | 255.255.0.0 | 192.168.0.0 – 192.168.255.255 | Private class C addressing | |
| 224.0.0.0/4 | 240.0.0.0 | 224.0.0.0 - | Global multicast | |
| 255.255.255.255/32 | 255.255.255.255 | N/A | Global Broadcast |
Subnets
| CIDR | Subnet Mask | Wildcard | Total IPs (-2*) |
|---|---|---|---|
| /32 | 255.255.255.255 | 0.0.0.0 | 1 |
| /31 | 255.255.255.254 | 0.0.0.1 | 2 |
| /30 | 255.255.255.252 | 0.0.0.3 | 4 |
| /29 | 255.255.255.248 | 0.0.0.7 | 8 |
| /28 | 255.255.255.240 | 0.0.0.15 | 16 |
| /27 | 255.255.255.224 | 0.0.0.31 | 32 |
| /26 | 255.255.255.192 | 0.0.0.63 | 64 |
| /25 | 255.255.255.128 | 0.0.0.127 | 128 |
| /24 | 255.255.255.0 | 0.0.0.255 | 256 |
| /23 | 255.255.254.0 | 0.0.1.255 | 512 |
| /22 | 255.255.252.0 | 0.0.3.255 | 1024 |
| /21 | 255.255.248.0 | 0.0.7.255 | 2048 |
| /20 | 255.255.240.0 | 0.0.15.255 | 4096 |
| /19 | 255.255.224.0 | 0.0.31.255 | 8192 |
| /18 | 255.255.192.0 | 0.0.63.255 | 16384 |
| /17 | 255.255.128.0 | 0.0.127.255 | 32768 |
| /16 | 255.255.0.0 | 0.0.255.255 | 65536 |
| /15 | 255.254.0.0 | 0.1.255.255 | 131072 |
| /14 | 255.252.0.0 | 0.3.255.255 | 262144 |
| /13 | 255.248.0.0 | 0.7.255.255 | 524288 |
| /12 | 255.240.0.0 | 0.15.255.255 | 1048576 |
| /11 | 255.224.0.0 | 0.31.255.255 | 2097152 |
| /10 | 255.192.0.0 | 0.63.255.255 | 4194304 |
| /9 | 255.128.0.0 | 0.127.255.255 | 8388608 |
| /8 | 255.0.0.0 | 0.255.255.255 | 16777216 |
| /7 | 254.0.0.0 | 33554432 | |
| /6 | 252.0.0.0 | 67108864 | |
| /5 | 248.0.0.0 | 134217728 | |
| /4 | 240.0.0.0 | 268435456 | |
| /3 | 224.0.0.0 | 536870912 | |
| /2 | 192.0.0.0 | 1073741824 | |
| /1 | 128.0.0.0 | 2147483648 |
- -2 for the number of usable IPs
Notes
| Note | Definition |
|---|---|
| # of subnets | 2n |
| # of hosts | 2(32-n) |
| Block size | 256 - subnet mask |
| Broadcast Addr | last addr in subnet |
| Usable Hosts | Between network addr and broadcast |