IPV4

Classful Address

binary	decimal
0xxxxxx . xxxxxxxx . xxxxxxxx . xxxxxxxx	0~127.x.x.x
10xxxxx . xxxxxxxx . xxxxxxxx . xxxxxxxx	128~191.x.x.x
110xxxxx . xxxxxxxx . xxxxxxxx . xxxxxxxx	224~239.x.x.x
1110xxxx . xxxxxxxx . xxxxxxxx . xxxxxxxx	224~239.x.x.x
11110000 . xxxxxxxx . xxxxxxxx . xxxxxxxx	240~255.x.x.x

special address

• Broadcasting

  • 255 . 255 . 255 . 255
  • network address . 255

• Loopback(in class A address range)

  • 127.x.x.x

• Unspecified(in class A address range)

  • 0.0.0.0

• Current Network(in class A address range)

  • 0 . host address

• Current Host

  • network address . 0

Subnet Mask

slash	binary	decimal	ipclass
/8	11111111 . 00000000 . 00000000 . 00000000	255.0.0.0	A
/16	11111111 . 11111111 . 00000000 . 00000000	255.255.0.0	B
/24	11111111 . 11111111 . 11111111 . 00000000	255.255.255.0	C

Why Subnet Mask?

• distinction what class of this ip it is.
• discrimination local or remote this ip it is.

Caculation

$C=IP_{a.net} \oplus SM_{a} - IP_{b.net}\oplus SM_{a} \\ \begin{cases} C=0 & local \\ C \neq 0 & remote \end{cases}$

CIDR

CIDR notation	netmask 2	netmask 10
/1	10000000 . 00000000 . 00000000 . 00000000	128 . 0 . 0 . 0
/2	11000000 . 00000000 . 00000000 . 00000000	192 . 0 . 0 . 0
/3	11100000 . 00000000 . 00000000 . 00000000	224 . 0 . 0 . 0
/4	11110000 . 00000000 . 00000000 . 00000000	240 . 0 . 0 . 0
/5	11111000 . 00000000 . 00000000 . 00000000	248 . 0 . 0 . 0
/6	11111100 . 00000000 . 00000000 . 00000000	252 . 0 . 0 . 0
/7	11111110 . 00000000 . 00000000 . 00000000	254 . 0 . 0 . 0
/8	11111111 . 00000000 . 00000000 . 00000000	255 . 0 . 0 . 0
/9	11111111 . 10000000 . 00000000 . 00000000	255 . 128 . 0 . 0
/10	11111111 . 11000000 . 00000000 . 00000000	255 . 192 . 0 . 0
/11	11111111 . 11100000 . 00000000 . 00000000	255 . 224 . 0 . 0
/12	11111111 . 11110000 . 00000000 . 00000000	255 . 240 . 0 . 0
/13	11111111 . 11111000 . 00000000 . 00000000	255 . 248 . 0 . 0
/14	11111111 . 11111100 . 00000000 . 00000000	255 . 252 . 0 . 0
/15	11111111 . 11111110 . 00000000 . 00000000	255 . 254 . 0 . 0
/16	11111111 . 11111111 . 00000000 . 00000000	255 . 255 . 0 . 0
/17	11111111 . 11111111 . 10000000 . 00000000	255 . 255 . 128 . 0
/18	11111111 . 11111111 . 11000000 . 00000000	255 . 255 . 192 . 0
/19	11111111 . 11111111 . 11100000 . 00000000	255 . 255 . 224 . 0
/20	11111111 . 11111111 . 11110000 . 00000000	255 . 255 . 240 . 0
/21	11111111 . 11111111 . 11111000 . 00000000	255 . 255 . 248 . 0
/22	11111111 . 11111111 . 11111100 . 00000000	255 . 255 . 252 . 0
/23	11111111 . 11111111 . 11111110 . 00000000	255 . 255 . 254 . 0
/24	11111111 . 11111111 . 11111111 . 00000000	255 . 255 . 255 . 0
/25	11111111 . 11111111 . 11111111 . 10000000	255 . 255 . 255 . 128
/26	11111111 . 11111111 . 11111111 . 11000000	255 . 255 . 255 . 192
/27	11111111 . 11111111 . 11111111 . 11100000	255 . 255 . 255 . 224
/28	11111111 . 11111111 . 11111111 . 11110000	255 . 255 . 255 . 240
/29	11111111 . 11111111 . 11111111 . 11111000	255 . 255 . 255 . 248
/30	11111111 . 11111111 . 11111111 . 11111100	255 . 255 . 255 . 252
/31	11111111 . 11111111 . 11111111 . 11111110	255 . 255 . 255 . 254

Why CIDR?

Think we have 2000 hosts need to distribution ipaddress.

If use class B address there will have 65535 address; 65535-2000=63536 address is wasted.

If use class C address we need almost 8 class C address.

How CIDR?

1. Choose a Classful address can range all hosts.
2. Caculation how many bits(host address) are fit for.
3. Length of full host address-length of host address=subnet id

Example

Range=172.16.0.0

SM=11111111 . 11111111 . 00000000 . 00000000

hosts	Classful	CIDR
2000	Range=172.16.0.0=65536 SM=255 . 255 . 0 . 0 avail=65536-2=65534 waste=65536-2000=63536	SM=255 . 255 . [00000-11111]000.00000000 network id=172.16.0.0/5 waste=2048-2000=48 Unused=65536-2048=63488

VLSM

Why VLSM?

VLSM can divide a full class address to many subnet.

How VLSM?

1. Sort subnet according to number of hosts.
2. Subnet(divide) the given network id into the number of subnet we need.
3. Subneting(vlsm) the subnet to fit the number of nodes in each subnet.

Example

Range= 192.168.4.64/24

SM=11111111 . 11111111 . 11111111 . 00000000

subnet	hosts	cidr	vlsm
LAN2	55	SM=255 . 255 . 255 . 00000000 network id=192.168.4.0/26 waste=64-55=9	SM=255 . 255 . 255 . 00000000 network id=192.168.4.0/26 waste=64-55=9
LAN1	25	SM=255 . 255 . 255 . 01000000 network id=192.168.4.64/26 waste=64-25=39	dived 192.168.4.64/26 to 192.168.4.[010,011]/27 192.168.4.64/27 for LAN1 wast=32-25=7
LAN3	12	SM=255 . 255 . 255 . 10000000 network id=192.168.4.128/26 waste=64-12=52	dived 192.168.4.96/27 to 192.168.4.[0110,0111]/28 192.168.4.96/28 for LAN3 wast=16-12=4
NoUse		SM=255 . 255 . 255 . 11000000 network id=192.168.4.196/26 64	255 . 255 . 255 . 10000000/26 255 . 255 . 255 . 11000000/26 255 . 255 . 255 . 0111xxxx/28 64+64+16=144
Waste		9+39+52=100	9+7+4=20
Total	55+25+12=92	92+64+100=256	92+144+20=256