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IP Addressing/Subnetting Simplified Brian Sterck May 6, 2005
| Date post: | 01-Nov-2014 |
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IP Addressing/Subnetting Simplified
Brian Sterck
May 6, 2005
Class ASubnetting
Options
Class BSubnetting
Options
Class CSubnetting
Options
Brain Benders
More Tools…
Practical Example
6 Nodes
23 Nodes
19 Nodes
17 Nodes
14 Nodes
10 Nodes
VLSM Exercise 1192.168.20.0 /24
Internet
14 Nodes
Do we have enough addresses?
• How many addresses have been allocated?
• How many are needed?
Address Allocation
• Total Address Needed:
LANs = 14+10+19+23+6+17+14 = 103
WANs = 4+4+4+4+4+4 = 24
Total = 103 + 24 = 127
Understanding IP Requirements
• Subnetworks on the LAN/WAN need to be issued using perfect powers of 2
• 22 = 4• 23 = 8• 24 = 16• 25 = 32• 26 = 64• 27 = 128
Scaling Subnets
• With a requirement of 23 nodes…
• The next perfect power of 2 that meets this need = 32
• 25 = 32 5 host bits needed
• Last Octet is then represented as:– A.B.C.NNNHHHHH N=Network H=Host– 11111111.11111111.11111111.11100000
Subnetting Examples
SubnetMask SubnetMask # Hosts
255.255.255.0 /24 256 (254)
255.255.255.128 /25 128 (126)
255.255.255.192 /26 64 (62)
255.255.255.224 /27 32 (30)
255.255.255.240 /28 16 (14)
255.255.255.248 /29 8 (6)
255.255.255.252 /30 4 (2)
Practical Example
6 Nodes
23 Nodes
19 Nodes
17 Nodes
14 Nodes
10 Nodes
VLSM Exercise 1192.168.20.0 /24
Internet
14 Nodes
/28
/28
/27
/27
/28
/27
/29
/30/30
/30/30
/30
/30
Address Allocation
• Total Addresses Needed:
LANs = 16+16+32+32+8+32+16 = 152
= /28 + /28 + /27 + /27 + /29 + /27 + /28 = 152
WANs = 4+4+4+4+4+4 = 24
= /30 + /30 + /30 + /30 + /30 + /30 = 24
Total = 103 + 52 = 157
Reference Points
• Use numbers, symbols, letters to represent each LAN / WAN link
• Use some consistent method for assignment– Size of Subnetwork– Location– Zone or Distribution Point
1
A1
Assign Reference Points
6 Nodes
23 Nodes
19 Nodes
17 Nodes
14 Nodes
10 Nodes
VLSM Exercise 1192.168.20.0 /24
Internet
14 Nodes
/28
/28
/27
/27
/28
/27
/29
/30/30
/30/30
/30
/30
1
2
3
4
5
6
7
8
9
10
11
12
13
Subnetting Options/24
/25 /25
/26 /26
/27 /27 /27 /27
/26 /26
/27 /27 /27 /27
/28 /28
/29 /29
/30 /30/30 /30
/29 /29
/30 /30/30 /30
Subnetting Options (cont.)
/24
/25 /25
/26 /26
/27 /27 /27 /27
/26 /26
/27 /27 /27 /27
/30 /30/30 /30/30 /30/30 /30
VLSM and Routing Protocols
• Does your routing protocol support varying the length of the subnet mask from one interface to another?
• Can you re-subnet a subnet differently from one interface to another and still advertise that subnetwork via RIPv1, RIPv2, OSPF, EIGRP, ISIS, BGP?
Routing Protocols
• Supporting VLSM– RIP version 2– EIGRP– OSPF– ISIS
• Not Supporting VLSM– IGRP– RIP version 1
Which Routing Protocols will advertise all Networks correctly?
Internet Service Provider
Frame-Relay ServiceT1 Link
ISDN Cloud128K
Point-to-PointPPP 512k Link192.168.16.0 /30
.2 .1
192.168.16.16 /30
.18 .17
192.168.32.64 /26
192.168.33.96/27
192.168.33.128 /27
192.168.16.8 /30
.9
.10
.97.129
.65192.168.65.192 /26
192.168.64.128 /25192.168.64.0 /25
.130
.129.1
.193
.129
192.168.65.128 /26
Non-VLSM capable Routing Protocols will work just fine!
Internet Service Provider
Frame-Relay ServiceT1 Link
ISDN Cloud128K
Point-to-PointPPP 512k Link
192.168.16.0 /30
.2 .1
192.168.16.16 /30
.18 .17
192.168.32.64 /26
192.168.33.96/27
192.168.33.128 /27
192.168.16.8 /30
.9
.10
.97.129
.65192.168.65.192 /26
192.168.64.128 /25192.168.64.0 /25
.130
.129.1
.193
.129
192.168.65.128 /26
Same Major Network = 192.168.33.0 /24
6 Nodes
23 Nodes
19 Nodes
17 Nodes
14 Nodes
10 Nodes
VLSM Exercise 1192.168.20.0 /24
Internet
14 Nodes
/28
/28
/27
/27
/28
/27
/29
/30/30
/30/30
/30
/30
1
2
3
4
5
6
7
8
9
10
11
12
13
Problem!
• The 192.168.20.0 /24 network gives us:– 1 Network– 254 Nodes Available for Assignment
• 13 Subnetworks Required
• Network Demands range from 4 – 32 nodes per LAN / WAN segment
Start Subnetting
192.168.20.0 255.255.255.0
0 0 0 0 0 0 0 0
Subnetting
Largest Network required = /2732 Nodes
192.168.20.0 255.255.255.0
0 0 0 0 0 0 0 0
2 3 = 8
2 5 = 32
Subnetting
Largest Network required = /2732 Nodes
2 3 = 8
2 5 = 32
192.168.20.0 255.255.255.0
0 0 0 0 0 0 0 0
Net Host
Box Diagram Alternate
.0
.255
192.168.20.0 /24
Address Range
.0
.255
192.168.20.0 /24
.0
.255
192.168.20.0 /24
.127
.128
.0
.255
192.168.20.0 /24
.127
.128
/24
/25 /25
.0
.255
192.168.20.0 /24
.127
.128
/25
/25
126 Nodes
126 Nodes
.0
.255
192.168.20.0 /24
.127
.128
/25
/26
126 Nodes
62 Nodes 62 Nodes
.191
.192
/26
/24
/25 /25
/26 /26
.0
.255
192.168.20.0 /24
.127
.128
/25
/27
126 Nodes
30 Nodes
62 Nodes
.191
.192
/26/27
30 Nodes.159
.160
.0
.255
192.168.20.0 /24
.127
.128
.191
.192
.159
.160
/24
/25 /25
/26 /26
/27 /27
23 Nodes
19 Nodes
/27
/27
/30
1
2
9
.0
.255
192.168.20.0 /24
.127
.128
/25
/27
126 Nodes
30 Nodes
62 Nodes
.191
.192
/26/27
30 Nodes.159
.160
1
.0
.255
192.168.20.0 /24
.127
.128
/25
/27
126 Nodes
30 Nodes
62 Nodes
.191
.192
/26/27
30 Nodes.159
.160
1
2
.0
.255
192.168.20.0 /24
.127
.128
/25
/27
126 Nodes
30 Nodes.191
.192
/27
30 Nodes.159
.160
1
2
/27
30 Nodes
3
.223
.224/27
30 Nodes
6 Nodes
23 Nodes
19 Nodes
17 Nodes
14 Nodes
10 Nodes
VLSM Exercise 1192.168.20.0 /24
Internet
14 Nodes
/28
/28
/27
/27
/28
/27
/29
/30/30
/30/30
/30
/30
1
2
3
4
5
6
7
8
9
10
11
12
13
.0
.255
192.168.20.0 /24
.127
.128
/25
/27
126 Nodes
30 Nodes.191
.192
/27
30 Nodes.159
.160
1
2
/27
30 Nodes
3
.223
.224
.239
.240/28
14 Nodes
4 /28
.0
.255
192.168.20.0 /24
.127
.128
/27
30 Nodes.191
.192
/27
30 Nodes.159
.160
1
2
/27
30 Nodes
3
.223
.224
.239
.240/28
14 Nodes
4 /28
.63
.64
.95
.96
/27
/27
/26
.0
.255
192.168.20.0 /24
.127
.128
/27
30 Nodes.191
.192
/27
30 Nodes.159
.160
1
2
/27
30 Nodes
3
.223
.224
.239
.240/28
14 Nodes
4 /28
.63
.64
.95
.96
/27
/28
14 Nodes
5
/28
14 Nodes
6
.79
.80
/26
.0
.255
192.168.20.0 /24
.127
.128
/27
30 Nodes.191
.192
/27
30 Nodes.159
.160
1
2
/27
30 Nodes
3
.223
.224
.239
.240/28
14 Nodes
4 /28
.63
.64
.95
.96
/28
14 Nodes
5
/28
14 Nodes
6
.79
.80
/26
.111
.112
/28.103
.104
7 /29
/29
.0
.255
192.168.20.0 /24
.128
/27
30 Nodes.191
.192
/27
30 Nodes.159
.160
1
2
/27
30 Nodes
3
.223
.224
.239
.240/28
14 Nodes
4 /28
.63
.64
.95
.96
/28
14 Nodes
5
/28
14 Nodes
6
.79
.80
/26.112
.1037 /29
/30
.115
.116
.119
.120
.123
.104
.107
.108
.111
.124
.127/30 /30 /30
/30 /30
.0
.255
192.168.20.0 /24
.128
/27
30 Nodes.191
.192
/27
30 Nodes.159
.160
1
2
/27
30 Nodes
3
.223
.224
.239
.240/28
14 Nodes
4 /28
.63
.64
.95
.96
/28
14 Nodes
5
/28
14 Nodes
6
.79
.80
/26.112
.1037 /29
/30
.115
.116
.119
.120
.123
.104
.107
.108
.111
.124
.1278 9
10 11
12 13
/30/30
/30 /30 /30
6 Nodes
23 Nodes
19 Nodes
17 Nodes
14 Nodes
10 Nodes
VLSM Exercise 1192.168.20.0 /24
Internet
14 Nodes
/28
/28
/27
/27
/28
/27
/29
/30/30
/30/30
/30
/30
1
2
3
4
5
6
7
8
9
10
11
12
13
Future Expansion Danger
• Note the three locations with the and
• If we need to add a network printer or visitor with laptop, the IP addressing scheme will have to be modified.
• This results in downtime and careful migration planning
There must be a better way!
.0
.255
192.168.20.0 /24
.128
/27
30 Nodes.191
.192
/27
30 Nodes.159
.160
1
2
/28
.223
.224
.239
.240
4
/28
.127
/25
126 Nodes
.207
.208/28
14 Nodes
/28
.0
.255
192.168.20.0 /24
.128
/27
30 Nodes.191
.192
/27
30 Nodes.159
.160
1
2
/28
.223
.224
.239
.240
4
/28
.127
/25
126 Nodes
.207
.208/28
14 Nodes
/28
.0
.255
192.168.20.0 /24
.128
/27
30 Nodes.191
.192
/27
30 Nodes.159
.160
1
2
/28
.223
.224
.239
.240
4
/28
.127
/25
126 Nodes
.207
.208/28
14 Nodes
/29
.231
.232
/29
6
.0
.255
192.168.20.0 /24
.128
/27
30 Nodes.191
.192
/27
30 Nodes.159
.160
1
2
/28
.223
.224
.239
.240
4
/28
.127
/25
126 Nodes
.207
.208/28
14 Nodes
/29
.231
.232/29
6
.0
.255
192.168.20.0 /24
.128
/27
30 Nodes.191
.192
/27
30 Nodes.159
.160
1
2
/28
.223
.224
.239
.240
4
/28
.127
.207
.208/28
14 Nodes
/29
.231
.232/29
6
.63
.64
.95
.96
/27
30 Nodes
/27
/26
3
.0
.255
192.168.20.0 /24
.128
/27
30 Nodes.191
.192
/27
30 Nodes.159
.160
1
2
/28
.223
.224
.239
.240
4
/28
.127
.207
.208/28
14 Nodes
/29
.231
.232/29
6
.63
.64
.95
.96
/27
30 Nodes
/28
/26
3
.80
.79
/29
.87
.88
/29
7
.0
.255
192.168.20.0 /24
.128
/27
30 Nodes.191
.192
/27
30 Nodes.159
.160
1
2
/28
.223
.224
.239
.240
4
/28
.127
.207
.208/28
14 Nodes
/29
.231
.232/29
6
.63
.64
.95
.96
/27
30 Nodes
/28
3
.80
.79
/29
.87
.88
/29
7
.32
.31
/27
.47
.48
5
14 Nodes
/28
.0
.255
192.168.20.0 /24
.128
/27
30 Nodes.191
.192
/27
30 Nodes.159
.160
1
2
/28
.223
.224
.239
.240
4
/29
.127
.207
.208/28
14 Nodes
/29
.231
.232/29
6
.63
.64
.95
.96
/27
30 Nodes
/28
3
.80
.79
/29
.87
.88
/29
7
.32
.31
/27
.47
.48
5
14 Nodes
/28
.247
.248
.243
.244
8 9
.0
.255
192.168.20.0 /24
.128
/27
30 Nodes.191
.192
/27
30 Nodes.159
.160
1
2
/28
.223
.224
.239
.240
4
/29
.127
.207
.208/28
14 Nodes
/29
.231
.232/29
6
.63
.95
.96
/27
30 Nodes
3
.80 /29
.87
.88
/29
7
.32
.31
.47
.48
5
14 Nodes
/28
.247
.248
.243
.244
8 9
.79
.64
/29
.71
.72
.67
.68
13 /30.3
.4
.7
.8
.11
.12
.15
/2810
11 12
6 Nodes
23 Nodes
19 Nodes
17 Nodes
14 Nodes
10 Nodes
VLSM Exercise 1192.168.20.0 /24
Internet
14 Nodes
/28
/28
/27
/27
/28
/27
/29
/30/30
/30/30
/30
/30
1
2
3
4
5
6
7
8
9
10
11
12
13
Summary Address192.168.20.128 /25
